Next Article in Journal
Evaluation of the forAge Age-at-Death Estimation Program Using Pubic Symphyseal Surface in a Korean Population
Previous Article in Journal
One Incremental Stride for Doxycycline, One Substantial Advancement for Thyroid Eye Disease
Previous Article in Special Issue
Preanalytical, Analytical and Postanalytical Analyses on Corynebacterium spp. and Actinomycetaceae in Urine Samples of Patients with Suspected Urinary Tract Infection—A Hypothesis-Forming Observational Study
 
 
Search for Articles:
Title / Keyword
Author / Affiliation / Email
Journal
Article Type
 
 
Advanced Search
 
Section
Special Issue
Volume
Issue
Number
Page
 
Journals
Diagnostics
Volume 14
Issue 8
10.3390/diagnostics14080792
diagnostics-logo
Submit to this Journal Review for this Journal Propose a Special Issue
► Article Menu

Article Menu

share Share announcement Help format_quote Cite question_answer Discuss in SciProfiles thumb_up
...
Endorse textsms
...
Comment
first_page
settings
Order Article Reprints
Font Type:
Arial Georgia Verdana
Font Size:
Aa Aa Aa
Line Spacing:
Column Width:
Background:
Article

Clinical and Microbiologic Analysis of Klebsiella pneumoniae Infection: Hypermucoviscosity, Virulence Factor, Genotype, and Antimicrobial Susceptibility

by
Miri Hyun
,
Ji Yeon Lee
and
Hyun Ah Kim
*
Department of Infectious Diseases, Keimyung University Dongsan Hospital, Keimyung University School of Medicine and Institute for Medical Science, Keimyung University, Daegu 42601, Republic of Korea
*
Author to whom correspondence should be addressed.
Diagnostics 2024, 14(8), 792; https://doi.org/10.3390/diagnostics14080792
Submission received: 24 February 2024 / Revised: 29 March 2024 / Accepted: 8 April 2024 / Published: 10 April 2024
(This article belongs to the Special Issue One Health Approach to Diagnose and Treat Fungal/Bacterial Infections)
Browse Figures
Review Reports Versions Notes

Abstract

:
Hypervirulent Klebsiella pneumoniae (KP) is defined according to hypermucoviscosity or various virulence factors and is clinically associated with community-acquired liver abscess (CLA). In this study, we investigated the clinical and microbiological characteristics of KP and significant factors associated with hypervirulence. The clinical characteristics, antimicrobial susceptibility, hypermucoviscosity, serotypes, hypervirulence-related genes, and biofilm formation of 414 KP isolates collected from the Keimyung University Dongsan Hospital between December 2013 and November 2015 were analyzed according to CLA. Significant risk factors for hypervirulent KP (HvKP) associated with CLA were investigated using logistic regression analysis. Notably, 155 (37.4%) isolates were hypermucoviscous, and 170 (41.1%) harbored aerobactin. CLA was present in 34 cases (8.2%). Epidemiology and treatment outcomes did not differ significantly between the CLA and non-CLA groups. The CLA group had significantly higher antibiotic susceptibility, K1/K2, rmpA, magA, allS, kfu, iutA, string test-positive result, and biofilm mass. Multivariate logistic regression revealed rmpA (OR, 5.67; 95% CI, 2.09–15.33; p = 0.001), magA (OR, 2.34; 95% CI, 1.01–5.40; p = 0.047), and biofilm mass >0.80 (OR, 2.13; 95% CI, 1.00–4.56; p = 0.050) as significant risk factors for CLA. rmpA was identified as the most significant risk factor for CLA among KP strains, implying that it is an important factor associated with HvKP.

1. Introduction

Klebsiella pneumoniae is a Gram-negative bacterium associated with an invasive syndrome that has caused liver abscesses in Southeast Asian populations over the past three decades [1,2,3]. Hypervirulent K. pneumoniae was first described in a patient with a liver abscess in Taiwan in the 1980s [4]. At that time, hypervirulence was defined based on hypermucoviscosity, which was confirmed by a string test, a phenotypic screening marker [5,6]. When hypervirulent K. pneumoniae first presented, it had the tendency to display low antimicrobial resistance, was associated with community-acquired infections, and was associated with the virulence factor rmpA and biofilm formation [4,7,8,9]. Hypervirulent K. pneumoniae has distinctive features compared with classic K. pneumoniae. Characteristics of classical K. pneumoniae infection were hospital-acquired infections, including pneumonia and urinary tract infections, and higher antimicrobial resistance rates [10,11].
Many studies on hypervirulent K. pneumoniae have been conducted over the years, and some researchers suggested that not only hypermucoviscosity but also aerobactin could be used to evaluate hypervirulence [12,13,14]. Aerobactin is a representative siderophore, and its production plays an important role in determining the hypervirulence of K. pneumoniae [15]. In several studies, the hypervirulent K. pneumoniae strains have been defined according to either aerobactin positivity or both hypermucoviscosity and aerobactin positivity [14,15,16].
In previous reports, the definition of hypervirulent K. pneumoniae varies depending on the definition used by each researcher, and there is still no consensus. Therefore, the proportion of hypervirulent K. pneumoniae inevitably depends on the definition used by each investigator [5,6,12,13,15,16,17]. For example, the prevalence of hypervirulent K. pneumoniae has been reported to vary from 12% to 58% in Southeast Asia [5,18,19,20,21,22].
Regarding the clinical aspect, hypervirulent K. pneumoniae is associated with community-acquired infections such as liver abscesses. Russo et al. [14] conducted a study in North America and the United Kingdom, defining hypervirulent K. pneumoniae based on the clinical diagnosis of tissue invasive infection. According to the results of the study, peg-344, siderophore-related virulence factors, and rmpA were some of the factors with the highest accuracy, sensitivity, and specificity in identifying hypervirulent K. pneumoniae. The string test had relatively low accuracy, sensitivity, and specificity (0.90, 0.89, and 0.91, respectively). K1 and K2 capsular serotypes had high specificity, but both accuracy and sensitivity were low [14]. The capsular serotypes of K. pneumoniae, such as K1 and K2, were reported to account for more than half of hypervirulent K. pneumoniae [9,23]. K1 and K2 serotypes have shown differences in clinical presentations, antimicrobial resistance rates, and molecular characteristics [18,24,25,26,27]. The K1 serotype mostly belongs to clonal group 23 (CG23), whereas the genetic characteristics of K2 are more diverse than those of the K1 serotype, and K2 belongs to diverse clonal groups, such as CG65, CG 86, and CG 375 [28,29,30]. Therefore, in this study, we attempted to focus on the relationship between community-acquired liver abscess (CLA) and hypervirulent K. pneumoniae from a clinical perspective in South Korea. The purpose of this study was to investigate the clinical and microbiological characteristics of K. pneumoniae and important factors related to its hypervirulence in South Korea.

2. Methods

2.1. Study Participants

A total of 414 K. pneumoniae isolates recovered from specimens collected at the Keimyung University Dongsan Hospital, a 1018-bed hospital in Daegu, South Korea, between November 2013 and November 2015 were retrospectively analyzed. We identified K. pneumoniae isolated from clinical specimens twice a week. When a K. pneumoniae strain was isolated, the researcher determined whether it was a true pathogen through chart review and collected the strain. Specimens obtained from patients younger than 18 years old were excluded. Patients who were transferred to other hospitals were excluded because we could not evaluate the treatment outcomes. Isolates were obtained from each patient during the first diagnosis of K. pneumoniae infection, and subsequent infections in the same patient were not included in this study. The time of the symptom onset was identified through chart review. The infections were further categorized into community-acquired, healthcare-associated, and nosocomial infections. Community-acquired infections were defined as those in which symptoms occurred within 48 h after visiting the hospital. However, patients with community-acquired infections and healthcare-associated risk factors were categorized as having healthcare-associated infections. Healthcare-associated risk factors included hospitalization within 90 days, hemodialysis, intravenous medication in outpatient clinics, or residency in long-term care facilities. Nosocomial infections were defined as those in which symptoms occurred 48 h after a patient was admitted. All isolates were subcultured in Luria–Bertani broth (Difco, Becton Dickinson, Sparks, MD, USA) and frozen at −70 °C until subsequent use.

2.2. Study Design

Medical records were retrospectively analyzed to identify underlying diseases, predisposing factors, antibiotics used within the last 3 months, previous hospitalization, antimicrobial susceptibility, clinical presentations, currently administered antibiotics, and treatment outcomes of the patients. Acute kidney injury was defined as an increase in serum creatinine level by >0.3 mg/dL within 48 h, an increase in serum creatinine level to >1.5 times baseline within 7 days, or a decrease in urine volume to <0.5 mL/kg/h over 6 h. The McCabe–Jackson score was used as the criterion to predict the survival of patients based on the prognosis of the underlying diseases, which were classified as rapidly fatal, ultimately fatal, and nonfatal [31]. The early treatment outcome was determined after 72 h of empirical antibiotic treatment. Early treatment outcomes were classified as complete response, partial response, or treatment failure. A complete response was defined as an improvement in both clinical conditions, and laboratory findings such as level of white blood cell or C-reactive protein. A partial response was defined as either an improved clinical condition or improved laboratory findings. Treatment failure was defined as the worsening of both clinical conditions and laboratory findings. Death of a patient due to K. pneumoniae infection or a complication of the infection within 30 days was defined as an infection-related 30-day mortality. We compared the strains based on their hypermucoviscous phenotype and hypervirulence-associated genes.

2.3. Definitions of Hypervirulent K. pneumoniae

In this study, we defined hypervirulent K. pneumoniae as CLA from a clinical perspective. We analyzed the clinical and microbiological characteristics according to the CLA to determine which genotypes and phenotypes were most associated with the CLA group. In addition, as reference data, the results of a comparative analysis between the two definitions based on hypermucoviscosity and aerobactin positivity, which were previously known as hypervirulent K. pneumoniae definitions, were presented in the supplementary tables. A previous study showed that the capsular serotype tended to have high specificity but low accuracy and sensitivity, and because the factors affecting K. pneumoniae hypervirulence may have a complex effect on each other, the capsular serotype was excluded during multivariate analysis [14].

2.4. Detection of K. pneumoniae Hypermucoviscosity

The string test was performed to determine the hypermucoviscous phenotype [32]. The string test was positive when a bacteriologic inoculation loop could generate a viscous string >5 mm in length by stretching bacterial colonies on an agar plate (Figure 1).

2.5. Polymerase Chain Reaction

Capsular serotypes and virulence factors, including rmpA (461), magA (1283), allS (764), mrkD (340), ybtS (242), kfu (638), and iutA (920), were identified using multiplex polymerase chain reaction (PCR). Strains were serotyped as K1, K2, K5, K20, K54, or K57 or as non-determined when a specific serotype could not be identified. The primers for blaSHV-1a were used for the positive control reactions. Amplification was performed using a C1000 Thermal Cycler (Bio-Rad, Pleasanton, CA, USA). Crude DNA was prepared by the lysis of the colonies at 100 °C for 10 min in 500 mL of sterile distilled water, followed by centrifugation. The lysed supernatant was used for PCR. The PCR program comprised an initial activation step at 95 °C for 15 min, followed by 30 cycles of 94 °C for 30 s, 60 °C for 90 s, 72 °C for 60 s, and a final extension period at 72 °C for 10 min. The amplicons were separated via electrophoresis at 100 V for 2 h using a 2% agarose gel. Specific primers used to detect the alleles of the target gene sequences are listed in Table S1.

2.6. Biofilm Formation

Biofilm mass was determined using a microtiter plate assay and based on optical density (OD, 570 nm). To measure biofilm formation, the bacterial suspensions were incubated in 96-well plates. After overnight incubation at 37 °C for 24 h, crystal violet was added, thereby staining the biofilm purple. Biofilm mass was then measured using the corresponding OD570 nm of the supernatant following solubilization of crystal violet in 99% ethanol. We used Synergy/HTX Spectrophotometer (BioTek instrument, Inc. Winooski, VT, USA) for analysis of biofilm. Each strain was tested in triplicate, with a positive control of K. pneumoniae ATCC 700603 and a negative control of K. pneumoniae ATCC 13883.

2.7. Antimicrobial Susceptibility Test

The isolates were analyzed using an automated microbial identification (Vitek2 Gram-negative identification system; bioMerieux, Lyon, France) and susceptibility test system (Vitek2 AST-N224 system). Antimicrobial susceptibility profiles were determined based on the breakpoints recommended in the guidelines of the 2012 Clinical and Laboratory Standards Institute (CLSI). Extended-spectrum β-lactamase (ESBL) production was detected using an automated methodology based on the Vitek2 AST-N224 system, which was used to inoculate and incubate bacteria according to the manufacturer’s recommendations.

2.8. Statistical Analyses

Statistical analyses were performed using Statistical Package for the Social Sciences version 21.0 (IBM Corp., Armonk, NY, USA). Categorical variables were compared using the chi-squared test or Fisher’s exact test. For continuous variables, the normality of distribution was evaluated using the Kolmogorov–Smirnov test. The Mann–Whitney U test and independent t-test were performed for data that followed non-normal and normal distributions, respectively. Statistical significance was defined as p < 0.05. Risk factors for the CLA group were assessed and analyzed using logistic regression in the total group. An independent variable with p < 0.1 in the univariate analysis was included in the multivariate analysis, and a variable with a final p < 0.05 was considered a significant risk factor.

3. Results

3.1. Clinical and Microbiological Characteristics According to Hypermucoviscosity

In total, 414 K. pneumoniae isolates were included in this study (Figure 2). A hypermucoviscous phenotype was observed in 155 isolates (37.4%). Male sex was more strongly associated with the hypermucoviscous phenotype (69.0%) than with the string-negative group (54.4%) (p = 0.003). In underlying diseases, solid tumors were less associated with hypermucoviscous phenotype (p = 0.002). Based on the McCabe classification, ultimately, fatal disease was less frequently associated with the hypermucoviscous phenotype (p = 0.017). In predisposing factors, percutaneous catheter drainage (p = 0.006) and invasive procedures (p = 0.001) were associated with the hypermucoviscous phenotype.
In the infection category, the proportion of community-acquired infection was more associated with hypermucoviscous phenotype (p < 0.001). Nosocomial infection was more associated with the string-negative group (p < 0.001). Among infection sources, intra-abdominal infection was more strongly associated with the hypermucoviscous phenotype than with the string-negative group (p = 0.001), whereas urinary tract infection showed a weaker association (p < 0.001). Regarding clinical presentations, metastatic infection, severe sepsis and septic shock, concomitant bacteremia, and admission to the intensive care unit (ICU), no differences were observed between the two groups. There were also no significant differences in the treatment outcomes, treatment failure, infection-related 30-day mortality, or acute kidney injury (Table S1).
The rates of resistance to ciprofloxacin (p < 0.001), cefazolin (p < 0.001), cefotaxime (p < 0.001), ceftazidime (p < 0.001), piperacillin/tazobactam (p < 0.001), aztreonam (p < 0.001), and trimethoprim/sulfamethoxazole (p < 0.001) were lower in the hypermucoviscous phenotype. ESBL-producing strains were lower in the hypermucoviscous phenotype (p < 0.001) (Table S2).
Aerobactin positivity was identified in 122 hypermucoviscous phenotype isolates (78.7%) and 48 string-negative isolates (18.5%). Among the hypermucoviscous strains, 122 (78.7%) were rmpA-positive strains, and 48 (31.0%) were magA-positive. Biofilm formation did not differ significantly between the hypermucoviscous phenotype and string-negative groups (Table S2).

3.2. Clinical and Microbiological Characteristics According to Aerobactin Positivity

Aerobactin was detected in 170 isolates (41.1%). In underlying diseases, solid tumor (p < 0.001), chronic renal disease (p = 0.040), and solid-organ transplant (p = 0.018) were less associated with hypermucoviscous phenotype. In predisposing factors, L-tube (p = 0.003), recent operation (p = 0.002), and prior ICU admission within 1 month (p = 0.026) were less associated with the hypermucoviscous phenotype.
The proportion of community-acquired infection was more associated with the aerobactin-positive group (p < 0.001). Nosocomial infection was more associated with the aerobactin-negative group (p < 0.001). Regarding the infection source, intra-abdominal infection was more strongly associated with the aerobactin-positive group (p = 0.023), whereas urinary tract infection showed a weaker association (p < 0.001). In terms of clinical presentations, metastatic infection, concomitant bacteremia, and admission to ICU, no differences were observed between the two groups. Similarly, no significant differences were observed in the treatment outcomes, treatment failure, infection-related 30-day mortality, or acute kidney injury (Table S3).
The rates of resistance to ciprofloxacin (p < 0.001), cefazolin (p < 0.001), cefotaxime (p < 0.001), ceftazidime (p < 0.001), piperacillin/tazobactam (p < 0.001), aztreonam (p < 0.001), and trimethoprim/sulfamethoxazole (p < 0.001) were lower in the aerobactin-positive group. ESBL positivity was lower in the aerobactin-positive group (p < 0.001) (Table S4).
The hypermucoviscous phenotype was detected in 122 (71.8%) aerobactin-positive and 33 (13.5%) aerobactin-negative isolates. Overall, rmpA-positive and magA-positive strains accounted for 159 (93.5%) and 60 (35.3%) isolates in the aerobactin-positive group, respectively. Biofilm formation did not differ significantly between the two groups (Table S4).

3.3. Epidemiology and Clinical characteristics According to Community-Acquired Liver Abscess

CLA was detected in 34 isolates (8.2%). In epidemiology, there was no significant difference in male sex and age between the CLA and non-CLA groups. In underlying diseases, solid tumors (p = 0.022) and neurological disease (p = 0.012) were more associated with the non-CLA group (p = 0.022). Based on the McCabe classification, ultimately, fatal disease was less frequently associated with the CLA group (p = 0.004). In predisposing factors, percutaneous catheter drainage (p < 0.001), L-tube (p = 0.015), and invasive procedures (p < 0.001) were associated with the CLA group. In others, such as recent operation (p = 0.019) and cases of prior ICU admission within 1 month (p = 0.014) were associated with the non-CLA group.
In the category of infection, all infections in the CLA group were community-acquired infections, as defined. Regarding the infection source, all infections in the CLA group were intra-abdominal infections, as defined. In terms of clinical presentations, metastatic infection, severe sepsis and septic shock, and admission to ICU, no differences were observed between the two groups. The rate of concomitant bacteremia was significantly higher in the CLA group than in the non-CLA group (61.8% vs. 31.8%; p < 0.001). There were no significant differences in treatment outcomes, treatment failure, infection-related 30-day mortality, or acute kidney injury (Table 1).

3.4. Antimicrobial Susceptibility and Microbiological Characteristics According to Community-Acquired Liver Abscess

Regarding antimicrobial susceptibility, most antibiotics such as amoxicillin/clavulanate, aztreonam, cefazolin, cefepime, cefotaxime, ceftazidime, ciprofloxacin, piperacillin/tazobactam, and trimethoprim/sulfamethoxazole had significantly lower resistance to K. pneumonia in the CLA group than in the non-CLA group. ESBL positivity was lower in the CLA group than in the non-CLA group (p < 0.001) (Table 2).
In the serotype, K1 (58.8% vs. 15.0%; p < 0.001) and K2 (26.5% vs. 13.2%; p = 0.042) were significantly higher in the CLA group than in the non-CLA group. In the virulence gene analysis, rmpA (82.4% vs. 36.1%; p < 0.001), magA (47.1% vs. 12.4%; p < 0.001), allS (52.9% vs. 16.4%; p < 0.001), kfu (58.8% vs. 31.2%; p = 0.001), and aerobactin (79.4% vs. 37.6%; p < 0.001) were significantly related to the CLA group compared with the non-CLA group.
Phenotype analysis showed that the CLA group had a higher string test-positive result, indicating greater hypermucoviscosity than the non-CLA group (73.5% vs. 34.2%; p < 0.001). When comparing the biofilm mass in the two groups, the rate of biofilm mass ≥0.80 was significantly higher in the CLA group than in the non-CLA group (52.9% vs. 30.3%; p = 0.007).

3.5. Significant Virulence Factors for Community-Acquired Liver Abscess in K. pneumoniae

As mentioned in the Methods Section, hypervirulent in K. pneumoniae was defined as CLA in this study. In the univariate logistic regression analysis, string test-positive (odds ratio [OR], 5.34; 95% confidence interval [CI], 2.4–11.78; p < 0.001), iutA-positive (OR, 6.39; 95% CI, 2.71–15.06; p < 0.001), rmpA-positive (OR, 8.28; 95% CI, 3.34–20.49; p < 0.001), magA-positive (OR, 6.30; 95% CI, 3.01–13.19; p < 0.001), allS-positive (OR, 5.73; 95% CI, 2.77–11.86; p < 0.001), and kfu-positive results (OR, 3.15; 95% CI, 1.54–6.45; p = 0.002) and biofilm mass >0.80 (OR, 2.58; 95% CI, 1.27–5.25; p = 0.009) were significant factors (Table 3).
The multivariate logistic regression analysis revealed that rmpA (OR, 5.83; 95% CI, 2.15–15.78, p = 0.001) was the most statistically significant risk factor for CLA, followed by magA (OR, 2.34; 95% CI, 1.01–5.40, p = 0.047) and biofilm mass >0.80 (OR, 2.13; 95% CI, 1.00–4.56, p = 0.050) (Table 3).

4. Discussion

In this study, we found that the proportion of hypermucoviscosity and aerobactin gene expression of K. pneumoniae varies widely. The proportion of hypervirulence differed depending on the used definitions of hypervirulent K. pneumoniae whether hypermucoviscosity and aerobactin positivity or not. Significant factors in CLA, for which the definition of hypervirulent K. pneumoniae was first proposed, were rmpA, magA, and biofilm mass.
When comparing the two groups according to the string test, the characteristics of hypervirulent K. pneumoniae were similar to those already known. As with other study results, hypermucoviscosity and aerobactin positivity were not consistent [33]. The hypermucoviscous capsule of hypervirulent K. pneumoniae is a key factor of hypervirulence [34]. Hypermucoviscous capsule contributes to reduced human cell binding and evasion of neutrophil-mediated phagocytosis. Because of this mechanism, the overproduction of hypermucoviscous capsules by hypervirulent K. pneumoniae has been reported as an important factor that aids bacterial dissemination and metastatic infections in the host [35]. Capsules could be affected by various environments and conditions [36]. Several studies have shown that the string test is not an appropriate method for assessing K. pneumoniae hypervirulence [13,15,23,37].
When comparing the two groups according to aerobactin results, the characteristics of hypervirulent K. pneumoniae were similar to already known [13]. Hypervirulent K. pneumoniae is associated with the possession of large virulence plasmids [37]. Iron acquisition, increased capsule production, K1/K2 capsular serotypes, and the colibactin toxin have been identified as the four microbiological and genotypic characteristics of hypervirulent K. pneumoniae [37]. Among various microbiologic factors, the ability to acquire iron is essential for bacterial growth [38]. High-affinity iron uptake systems contribute to the virulence of K. pneumoniae [39]. Aerobactin is located on a large virulence plasmid of K. pneumoniae that is not present in most classic K. pneumoniae strains [40]. Aerobactin mediates the virulence of K. pneumoniae and accounts for increased siderophore production under iron-limiting conditions by hypervirulent K. pneumoniae [38]. Therefore, some researchers have used aerobactin-positive strains to define hypervirulent K. pneumoniae. However, aerobactin-positive strains do not completely correlate with the existing hypermucoviscous phenotype [12,13,16,41].
Owing to changes in the medical environment, findings that deviate from the previously reported characteristics of hypervirulent K. pneumoniae, such as an increase in antimicrobial resistance and the relationship between healthcare-associated infections, have been reported [15,21,42]. In cases of our study when only aerobactin was confirmed positive, and the string test was negative, the antimicrobial resistance rate tended to be higher compared to aerobactin-positive cases; thus, it can be assumed that the characteristics of the hypermucoviscous phenotype may be lost upon exposure to antibiotics [43]. In a Chinese study, hypervirulence was defined as a positive result for aerobactin, and approximately 75% of hypervirulent and 18% of classic K. pneumoniae strains were found to be string test-positive [13]. In another Chinese study, hypervirulent K. pneumoniae was defined as having both a hypermucoviscous phenotype and a positive result for aerobactin. In that study, the prevalences of rmpA and magA were found to be 81.3% and 78.8% in hypervirulent K. pneumoniae and 17.9% and 61.1% in classic K. pneumoniae, respectively [16].
Hypervirulent K. pneumoniae was distinguished from classic K. pneumoniae based on the clinical presentation of a community-acquired pyogenic liver abscess with metastatic infections, such as endophthalmitis, central nervous system involvement, lung involvement, and antimicrobial susceptible pathogen. [3,44,45]. The capsular serotype, determined by surface antigens, has also been reported as an important factor that may affect the virulence of K. pneumoniae [46]. Capsular serotypes of K1 and K2 in liver abscess and biofilm formation were more frequently associated with hypervirulent K. pneumoniae [7,47,48,49]. In pyogenic liver abscesses of K. pneumoniae, aerobactin was more correlated than hypermucoviscosity [50]. K1 and K2 are the predominant capsular serotypes of hypervirulent K. pneumoniae [27,51], with K1 being the most common capsular serotype, followed by K2 [9,52]. In several studies, K1 and K2 showed different expression of virulence factors, especially rmpA, magA, and aerobactin, and displayed higher levels of biofilm formation than other capsular serotypes [25,26,53]. The K1 serotype is associated with siderophore iron acquisition systems and invasive infections [18], whereas K2 has a higher diversity of sequence types [26,54,55].
Hypermucoviscosity is still being used as a criterion for hypervirulent K. pneumoniae in many studies [5,21,32,38]. Among the virulence factors, rmpA is particularly known to affect capsule production in hypervirulent K. pneumoniae [56]. Hypervirulent K. pneumoniae with mutations in rmpA lose hypermucoviscous phenotype and show a strong reduction in virulence [57]. Proportions of hypermucoviscosity and rmpA in the aerobactin-positive cases were similar to those of another study, and the distribution of other virulence factors, such as magA, was confirmed to be diverse [58]. Hypermucoviscosity, rmpA, aerobactin, and serotype K1 are useful laboratory markers when suspecting community-acquired K. pneumoniae bacteremic liver abscess [59]. In cases of K. pneumoniae liver abscess in China, all strains were rmpA-positive, and two-thirds of strains were magA-positive [60]. rmpA is specifically correlated with abscess formation in hypermucoviscous K. pneumoniae strains [61].
This study had several limitations. First, it was conducted retrospectively in a tertiary hospital, which may introduce bias in the data interpretation. Second, this study was conducted at a single center. These factors can significantly influence the results and their generalizability. Third, the patients admitted to a tertiary hospital may exhibit more severe symptoms than those in a primary medical center. As patients who were transferred to other hospitals were excluded, there was a limitation in determining the overall condition of patients with K. pneumoniae infections who visited our hospital. Finally, the number of analyzed strains was relatively low.
Despite these limitations, our findings determined that both definitions were useful, as they showed clinical and microbiological features suggestive of hypervirulent K. pneumoniae and that the virulence gene rmpA was significantly higher in CLA with hypervirulent K. pneumoniae. Additional discussion is needed in the future regarding the definition of hypervirulent K. pneumoniae.

Supplementary Materials

The following supporting information can be downloaded at https://www.mdpi.com/article/10.3390/diagnostics14080792/s1. Table S1: Baseline characteristics and clinical presentations of Klebsiella pneumoniae isolates according to hypermucoviscosity; Table S2: Antimicrobial resistance and microbiological characteristics of Klebsiella pneumoniae isolates according to hypermucoviscosity; Table S3: Baseline characteristics and clinical presentations of Klebsiella pneumoniae isolates according to aerobactin positivity; Table S4: Antimicrobial resistance and microbiological characteristics of Klebsiella pneumoniae isolates according to aerobactin positivity.

Author Contributions

Conceptualization, data curation, laboratory experiment, and methodology, M.H. and H.A.K.; formal analysis, M.H. and J.Y.L.; writing—review and editing, M.H., J.Y.L. and H.A.K. All authors have read and agreed to the published version of the manuscript.

Funding

This work was supported by the National Research Foundation of Korea (NRF) grant funded by the Korean government (MSIP) (NRF-2020R1F1A1070470).

Institutional Review Board Statement

The study was conducted in accordance with the Declaration of Helsinki and approved by the Institutional Review Board of Keimyung University Dongsan Medical Center (IRB no. 2022-05-040).

Informed Consent Statement

Patient consent was waived due to the retrospective nature of the study and the use of identifiable specimens.

Data Availability Statement

The dataset of the current study is available from the corresponding author upon request.

Acknowledgments

We would like to thank Eun-Sil Park for data entry.

Conflicts of Interest

The authors declare no conflicts of interest. The funders had no role in the design of the study; in the collection, analyses, or interpretation of data; in the writing of the manuscript; or in the decision to publish the results.

References

  1. Chang, F.Y.; Chou, M.Y.; Fan, R.L.; Shaio, M.F. A clinical study of Klebsiella liver abscess. Taiwan Yi Xue Hui Za Zhi 1988, 87, 282–287. [Google Scholar] [PubMed]
  2. Chang, F.Y.; Chou, M.Y. Comparison of pyogenic liver abscesses caused by Klebsiella pneumoniae and non-K. pneumoniae pathogens. J. Formos. Med. Assoc. 1995, 94, 232–237. [Google Scholar] [PubMed]
  3. Siu, L.K.; Yeh, K.M.; Lin, J.C.; Fung, C.P.; Chang, F.Y. Klebsiella pneumoniae liver abscess: A new invasive syndrome. Lancet Infect. Dis. 2012, 12, 881–887. [Google Scholar] [CrossRef] [PubMed]
  4. Liu, Y.C.; Cheng, D.L.; Lin, C.L. Klebsiella pneumoniae liver abscess associated with septic endophthalmitis. Arch. Intern Med. 1986, 146, 1913–1916. [Google Scholar] [CrossRef] [PubMed]
  5. Li, W.; Sun, G.; Yu, Y.; Li, N.; Chen, M.; Jin, R.; Jiao, Y.; Wu, H. Increasing occurrence of antimicrobial-resistant hypervirulent (hypermucoviscous) Klebsiella pneumoniae isolates in China. Clin. Infect. Dis. 2014, 58, 225–232. [Google Scholar] [CrossRef] [PubMed]
  6. Liu, Y.M.; Li, B.B.; Zhang, Y.Y.; Zhang, W.; Shen, H.; Li, H.; Cao, B. Clinical and molecular characteristics of emerging hypervirulent Klebsiella pneumoniae bloodstream infections in mainland China. Antimicrob. Agents Chemother. 2014, 58, 5379–5385. [Google Scholar] [CrossRef] [PubMed]
  7. Kong, Q.; Beanan, J.M.; Olson, R.; Macdonald, U.; Shon, A.S.; Metzger, D.J.; Pomakov, A.O.; Russo, T.A. Biofilm formed by a hypervirulent (hypermucoviscous) variant of Klebsiella pneumoniae does not enhance serum resistance or survival in an in vivo abscess model. Virulence 2012, 3, 309–318. [Google Scholar] [CrossRef] [PubMed]
  8. Casanova, C.; Lorente, J.A.; Carrillo, F.; Perez-Rodriguez, E.; Nunez, N. Klebsiella pneumoniae liver abscess associated with septic endophthalmitis. Arch. Intern Med. 1989, 149, 1467. [Google Scholar] [CrossRef]
  9. Fung, C.P.; Chang, F.Y.; Lee, S.C.; Hu, B.S.; Kuo, B.I.; Liu, C.Y.; Ho, M.; Siu, L.K. A global emerging disease of Klebsiella pneumoniae liver abscess: Is serotype K1 an important factor for complicated endophthalmitis? Gut 2002, 50, 420–424. [Google Scholar] [CrossRef]
  10. Moellering, R.C., Jr. NDM-1—A cause for worldwide concern. N. Engl. J. Med. 2010, 363, 2377–2379. [Google Scholar] [CrossRef]
  11. Conlan, S.; Thomas, P.J.; Deming, C.; Park, M.; Lau, A.F.; Dekker, J.P.; Snitkin, E.S.; Clark, T.A.; Luong, K.; Song, Y.; et al. Single-molecule sequencing to track plasmid diversity of hospital-associated carbapenemase-producing Enterobacteriaceae. Sci. Transl. Med. 2014, 6, 254ra126. [Google Scholar] [CrossRef] [PubMed]
  12. Russo, T.A.; Olson, R.; MacDonald, U.; Beanan, J.; Davidson, B.A. Aerobactin, but not yersiniabactin, salmochelin, or enterobactin, enables the growth/survival of hypervirulent (hypermucoviscous) Klebsiella pneumoniae ex vivo and in vivo. Infect. Immun. 2015, 83, 3325–3333. [Google Scholar] [CrossRef] [PubMed]
  13. Sheng, Z.; Li, J.; Chen, T.; Zhu, Y.; Yu, X.; He, X.; Zheng, Y.; Ma, C.; Zheng, M.; Wang, P.; et al. Clinical and Microbiological Characteristics of Klebsiella pneumoniae Bloodstream Infection in a Chinese Hospital: Hypervirulent and Multiclonal. Infect. Drug Resist. 2022, 15, 3981–3990. [Google Scholar] [CrossRef] [PubMed]
  14. Russo, T.A.; Olson, R.; Fang, C.T.; Stoesser, N.; Miller, M.; MacDonald, U.; Hutson, A.; Barker, J.H.; La Hoz, R.M.; Johnson, J.R. Identification of Biomarkers for Differentiation of Hypervirulent Klebsiella pneumoniae from Classical K. pneumoniae. J. Clin. Microbiol. 2018, 56, e00776-18. [Google Scholar] [CrossRef] [PubMed]
  15. Shankar, C.; Basu, S.; Lal, B.; Shanmugam, S.; Vasudevan, K.; Mathur, P.; Ramaiah, S.; Anbarasu, A.; Veeraraghavan, B. Aerobactin Seems To Be a Promising Marker Compared With Unstable RmpA2 for the Identification of Hypervirulent Carbapenem-Resistant Klebsiella pneumoniae: In Silico and In Vitro Evidence. Front. Cell. Infect. Microbiol. 2021, 11, 709681. [Google Scholar] [CrossRef] [PubMed]
  16. Liu, C.; Guo, J. Hypervirulent Klebsiella pneumoniae (hypermucoviscous and aerobactin positive) infection over 6 years in the elderly in China: Antimicrobial resistance patterns, molecular epidemiology and risk factor. Ann. Clin. Microbiol. Antimicrob. 2019, 18, 4. [Google Scholar] [CrossRef]
  17. Vandhana, V.; Saralaya, K.V.; Bhat, S.; Shenoy Mulki, S.; Bhat, A.K. Characterization of Hypervirulent Klebsiella pneumoniae (Hv-Kp): Correlation of Virulence with Antimicrobial Susceptibility. Int. J. Microbiol. 2022, 2022, 4532707. [Google Scholar] [CrossRef] [PubMed]
  18. Chen, Y.T.; Lai, Y.C.; Tan, M.C.; Hsieh, L.Y.; Wang, J.T.; Shiau, Y.R.; Wang, H.Y.; Lin, A.C.; Lai, J.F.; Huang, I.W.; et al. Prevalence and characteristics of pks genotoxin gene cluster-positive clinical Klebsiella pneumoniae isolates in Taiwan. Sci. Rep. 2017, 7, 43120. [Google Scholar] [CrossRef] [PubMed]
  19. Liu, Z.; Gu, Y.; Li, X.; Liu, Y.; Ye, Y.; Guan, S.; Li, J. Identification and Characterization of NDM-1-producing Hypervirulent (Hypermucoviscous) Klebsiella pneumoniae in China. Ann. Lab. Med. 2019, 39, 167–175. [Google Scholar] [CrossRef] [PubMed]
  20. Liu, C.; Shi, J.; Guo, J. High prevalence of hypervirulent Klebsiella pneumoniae infection in the genetic background of elderly patients in two teaching hospitals in China. Infect. Drug Resist. 2018, 11, 1031–1041. [Google Scholar] [CrossRef] [PubMed]
  21. Hyun, M.; Lee, J.Y.; Ryu, S.Y.; Ryoo, N.; Kim, H.A. Antibiotic Resistance and Clinical Presentation of Health Care-Associated Hypervirulent Klebsiella pneumoniae Infection in Korea. Microb. Drug Resist. 2019, 25, 1204–1209. [Google Scholar] [CrossRef] [PubMed]
  22. Liu, C.; Du, P.; Xiao, N.; Ji, F.; Russo, T.A.; Guo, J. Hypervirulent Klebsiella pneumoniae is emerging as an increasingly prevalent K. pneumoniae pathotype responsible for nosocomial and healthcare-associated infections in Beijing, China. Virulence 2020, 11, 1215–1224. [Google Scholar] [CrossRef] [PubMed]
  23. Shi, Q.; Lan, P.; Huang, D.; Hua, X.; Jiang, Y.; Zhou, J.; Yu, Y. Diversity of virulence level phenotype of hypervirulent Klebsiella pneumoniae from different sequence type lineage. BMC Microbiol. 2018, 18, 94. [Google Scholar] [CrossRef] [PubMed]
  24. Struve, C.; Roe, C.C.; Stegger, M.; Stahlhut, S.G.; Hansen, D.S.; Engelthaler, D.M.; Andersen, P.S.; Driebe, E.M.; Keim, P.; Krogfelt, K.A. Mapping the Evolution of Hypervirulent Klebsiella pneumoniae. mBio 2015, 6, e00630. [Google Scholar] [CrossRef] [PubMed]
  25. Yu, W.L.; Ko, W.C.; Cheng, K.C.; Lee, C.C.; Lai, C.C.; Chuang, Y.C. Comparison of prevalence of virulence factors for Klebsiella pneumoniae liver abscesses between isolates with capsular K1/K2 and non-K1/K2 serotypes. Diagn. Microbiol. Infect. Dis. 2008, 62, 1–6. [Google Scholar] [CrossRef]
  26. Harada, S.; Ishii, Y.; Saga, T.; Aoki, K.; Tateda, K. Molecular epidemiology of Klebsiella pneumoniae K1 and K2 isolates in Japan. Diagn. Microbiol. Infect. Dis. 2018, 91, 354–359. [Google Scholar] [CrossRef] [PubMed]
  27. Yeh, K.M.; Kurup, A.; Siu, L.K.; Koh, Y.L.; Fung, C.P.; Lin, J.C.; Chen, T.L.; Chang, F.Y.; Koh, T.H. Capsular serotype K1 or K2, rather than magA and rmpA, is a major virulence determinant for Klebsiella pneumoniae liver abscess in Singapore and Taiwan. J. Clin. Microbiol. 2007, 45, 466–471. [Google Scholar] [CrossRef]
  28. Catalan-Najera, J.C.; Garza-Ramos, U.; Barrios-Camacho, H. Hypervirulence and hypermucoviscosity: Two different but complementary Klebsiella spp. phenotypes? Virulence 2017, 8, 1111–1123. [Google Scholar] [CrossRef] [PubMed]
  29. Bialek-Davenet, S.; Criscuolo, A.; Ailloud, F.; Passet, V.; Jones, L.; Delannoy-Vieillard, A.S.; Garin, B.; Le Hello, S.; Arlet, G.; Nicolas-Chanoine, M.H.; et al. Genomic definition of hypervirulent and multidrug-resistant Klebsiella pneumoniae clonal groups. Emerg. Infect. Dis. 2014, 20, 1812–1820. [Google Scholar] [CrossRef] [PubMed]
  30. Passet, V.; Brisse, S. Association of tellurite resistance with hypervirulent clonal groups of Klebsiella pneumoniae. J. Clin. Microbiol. 2015, 53, 1380–1382. [Google Scholar] [CrossRef] [PubMed]
  31. McCabe, W.R. Endotoxin and bacteremia due to gram-negative organisms. N. Engl. J. Med. 1970, 283, 1342–1343. [Google Scholar] [CrossRef] [PubMed]
  32. Fang, C.T.; Chuang, Y.P.; Shun, C.T.; Chang, S.C.; Wang, J.T. A novel virulence gene in Klebsiella pneumoniae strains causing primary liver abscess and septic metastatic complications. J. Exp. Med. 2004, 199, 697–705. [Google Scholar] [CrossRef] [PubMed]
  33. Lan, P.; Yan, R.; Lu, Y.; Zhao, D.; Shi, Q.; Jiang, Y.; Yu, Y.; Zhou, J. Genetic diversity of siderophores and hypermucoviscosity phenotype in Klebsiella pneumoniae. Microb. Pathog. 2021, 158, 105014. [Google Scholar] [CrossRef] [PubMed]
  34. Dorman, M.J.; Feltwell, T.; Goulding, D.A.; Parkhill, J.; Short, F.L. The Capsule Regulatory Network of Klebsiella pneumoniae Defined by density-TraDISort. mBio 2018, 9, e01863-18. [Google Scholar] [CrossRef] [PubMed]
  35. Xu, Q.; Yang, X.; Chan, E.W.C.; Chen, S. The hypermucoviscosity of hypervirulent K. pneumoniae confers the ability to evade neutrophil-mediated phagocytosis. Virulence 2021, 12, 2050–2059. [Google Scholar] [CrossRef] [PubMed]
  36. Palacios, M.; Miner, T.A.; Frederick, D.R.; Sepulveda, V.E.; Quinn, J.D.; Walker, K.A.; Miller, V.L. Identification of Two Regulators of Virulence That Are Conserved in Klebsiella pneumoniae Classical and Hypervirulent Strains. mBio 2018, 9, e01443-18. [Google Scholar] [CrossRef] [PubMed]
  37. Choby, J.E.; Howard-Anderson, J.; Weiss, D.S. Hypervirulent Klebsiella pneumoniae—Clinical and molecular perspectives. J. Intern Med. 2020, 287, 283–300. [Google Scholar] [CrossRef] [PubMed]
  38. Russo, T.A.; Olson, R.; Macdonald, U.; Metzger, D.; Maltese, L.M.; Drake, E.J.; Gulick, A.M. Aerobactin mediates virulence and accounts for increased siderophore production under iron-limiting conditions by hypervirulent (hypermucoviscous) Klebsiella pneumoniae. Infect. Immun. 2014, 82, 2356–2367. [Google Scholar] [CrossRef] [PubMed]
  39. Koczura, R.; Kaznowski, A. Occurrence of the Yersinia high-pathogenicity island and iron uptake systems in clinical isolates of Klebsiella pneumoniae. Microb. Pathog. 2003, 35, 197–202. [Google Scholar] [CrossRef] [PubMed]
  40. Lee, C.R.; Lee, J.H.; Park, K.S.; Jeon, J.H.; Kim, Y.B.; Cha, C.J.; Jeong, B.C.; Lee, S.H. Antimicrobial Resistance of Hypervirulent Klebsiella pneumoniae: Epidemiology, Hypervirulence-Associated Determinants, and Resistance Mechanisms. Front. Cell. Infect. Microbiol. 2017, 7, 483. [Google Scholar] [CrossRef] [PubMed]
  41. Li, G.; Sun, S.; Zhao, Z.Y.; Sun, Y. The pathogenicity of rmpA or aerobactin-positive Klebsiella pneumoniae in infected mice. J. Int. Med. Res. 2019, 47, 4344–4352. [Google Scholar] [CrossRef] [PubMed]
  42. Gao, Q.; Shen, Z.; Qin, J.; Liu, Y.; Li, M. Antimicrobial Resistance and Pathogenicity Determination of Community-Acquired Hypervirulent Klebsiella pneumoniae. Microb. Drug Resist. 2020, 26, 1195–1200. [Google Scholar] [CrossRef] [PubMed]
  43. Lee, C.H.; Liu, J.W.; Su, L.H.; Chien, C.C.; Li, C.C.; Yang, K.D. Hypermucoviscosity associated with Klebsiella pneumoniae-mediated invasive syndrome: A prospective cross-sectional study in Taiwan. Int. J. Infect. Dis. 2010, 14, e688–e692. [Google Scholar] [CrossRef] [PubMed]
  44. Lederman, E.R.; Crum, N.F. Pyogenic liver abscess with a focus on Klebsiella pneumoniae as a primary pathogen: An emerging disease with unique clinical characteristics. Am. J. Gastroenterol. 2005, 100, 322–331. [Google Scholar] [CrossRef] [PubMed]
  45. Pomakova, D.K.; Hsiao, C.B.; Beanan, J.M.; Olson, R.; MacDonald, U.; Keynan, Y.; Russo, T.A. Clinical and phenotypic differences between classic and hypervirulent Klebsiella pneumonia: An emerging and under-recognized pathogenic variant. Eur. J. Clin. Microbiol. Infect. Dis. 2012, 31, 981–989. [Google Scholar] [CrossRef] [PubMed]
  46. Yeh, K.M.; Chiu, S.K.; Lin, C.L.; Huang, L.Y.; Tsai, Y.K.; Chang, J.C.; Lin, J.C.; Chang, F.Y.; Siu, L.K. Surface antigens contribute differently to the pathophysiological features in serotype K1 and K2 Klebsiella pneumoniae strains isolated from liver abscesses. Gut Pathog. 2016, 8, 4. [Google Scholar] [CrossRef] [PubMed]
  47. Cubero, M.; Grau, I.; Tubau, F.; Pallares, R.; Dominguez, M.A.; Linares, J.; Ardanuy, C. Hypervirulent Klebsiella pneumoniae clones causing bacteraemia in adults in a teaching hospital in Barcelona, Spain (2007–2013). Clin. Microbiol. Infect. 2016, 22, 154–160. [Google Scholar] [CrossRef] [PubMed]
  48. Zhang, Y.; Sun, J.; Mi, C.; Li, W.; Zhao, S.; Wang, Q.; Shi, D.; Liu, L.; Ding, B.; Chang, Y.F.; et al. First report of two rapid-onset fatal infections caused by a newly emerging hypervirulent K. Pneumonia ST86 strain of serotype K2 in China. Front. Microbiol. 2015, 6, 721. [Google Scholar] [CrossRef] [PubMed]
  49. Wu, M.C.; Lin, T.L.; Hsieh, P.F.; Yang, H.C.; Wang, J.T. Isolation of genes involved in biofilm formation of a Klebsiella pneumoniae strain causing pyogenic liver abscess. PLoS ONE 2011, 6, e23500. [Google Scholar] [CrossRef] [PubMed]
  50. Zhang, S.; Zhang, X.; Wu, Q.; Zheng, X.; Dong, G.; Fang, R.; Zhang, Y.; Cao, J.; Zhou, T. Clinical, microbiological, and molecular epidemiological characteristics of Klebsiella pneumoniae-induced pyogenic liver abscess in southeastern China. Antimicrob. Resist. Infect. Control 2019, 8, 166. [Google Scholar] [CrossRef] [PubMed]
  51. Holt, K.E.; Wertheim, H.; Zadoks, R.N.; Baker, S.; Whitehouse, C.A.; Dance, D.; Jenney, A.; Connor, T.R.; Hsu, L.Y.; Severin, J.; et al. Genomic analysis of diversity, population structure, virulence, and antimicrobial resistance in Klebsiella pneumoniae, an urgent threat to public health. Proc. Natl. Acad. Sci. USA 2015, 112, E3574–E3581. [Google Scholar] [CrossRef] [PubMed]
  52. Bilal, S.; Volz, M.S.; Fiedler, T.; Podschun, R.; Schneider, T. Klebsiella pneumoniae-induced liver abscesses, Germany. Emerg. Infect. Dis. 2014, 20, 1939–1940. [Google Scholar] [CrossRef] [PubMed]
  53. Cubero, M.; Marti, S.; Dominguez, M.A.; Gonzalez-Diaz, A.; Berbel, D.; Ardanuy, C. Hypervirulent Klebsiella pneumoniae serotype K1 clinical isolates form robust biofilms at the air-liquid interface. PLoS ONE 2019, 14, e0222628. [Google Scholar] [CrossRef] [PubMed]
  54. Liao, C.H.; Huang, Y.T.; Chang, C.Y.; Hsu, H.S.; Hsueh, P.R. Capsular serotypes and multilocus sequence types of bacteremic Klebsiella pneumoniae isolates associated with different types of infections. Eur. J. Clin. Microbiol. Infect. Dis. 2014, 33, 365–369. [Google Scholar] [CrossRef] [PubMed]
  55. Guo, Y.; Wang, S.; Zhan, L.; Jin, Y.; Duan, J.; Hao, Z.; Lv, J.; Qi, X.; Chen, L.; Kreiswirth, B.N.; et al. Microbiological and Clinical Characteristics of Hypermucoviscous Klebsiella pneumoniae Isolates Associated with Invasive Infections in China. Front. Cell. Infect. Microbiol. 2017, 7, 24. [Google Scholar] [CrossRef] [PubMed]
  56. Nassif, X.; Fournier, J.M.; Arondel, J.; Sansonetti, P.J. Mucoid phenotype of Klebsiella pneumoniae is a plasmid-encoded virulence factor. Infect. Immun. 1989, 57, 546–552. [Google Scholar] [CrossRef] [PubMed]
  57. Cheng, H.Y.; Chen, Y.S.; Wu, C.Y.; Chang, H.Y.; Lai, Y.C.; Peng, H.L. RmpA regulation of capsular polysaccharide biosynthesis in Klebsiella pneumoniae CG43. J. Bacteriol. 2010, 192, 3144–3158. [Google Scholar] [CrossRef] [PubMed]
  58. Lin, Z.W.; Zheng, J.X.; Bai, B.; Xu, G.J.; Lin, F.J.; Chen, Z.; Sun, X.; Qu, D.; Yu, Z.J.; Deng, Q.W. Characteristics of Hypervirulent Klebsiella pneumoniae: Does Low Expression of rmpA Contribute to the Absence of Hypervirulence? Front. Microbiol. 2020, 11, 436. [Google Scholar] [CrossRef] [PubMed]
  59. Tan, T.Y.; Ong, M.; Cheng, Y.; Ng, L.S.Y. Hypermucoviscosity, rmpA, and aerobactin are associated with community-acquired Klebsiella pneumoniae bacteremic isolates causing liver abscess in Singapore. J. Microbiol. Immunol. Infect. 2019, 52, 30–34. [Google Scholar] [CrossRef] [PubMed]
  60. Qu, T.T.; Zhou, J.C.; Jiang, Y.; Shi, K.R.; Li, B.; Shen, P.; Wei, Z.Q.; Yu, Y.S. Clinical and microbiological characteristics of Klebsiella pneumoniae liver abscess in East China. BMC Infect. Dis. 2015, 15, 161. [Google Scholar] [CrossRef] [PubMed]
  61. Yu, W.L.; Ko, W.C.; Cheng, K.C.; Lee, H.C.; Ke, D.S.; Lee, C.C.; Fung, C.P.; Chuang, Y.C. Association between rmpA and magA genes and clinical syndromes caused by Klebsiella pneumoniae in Taiwan. Clin. Infect. Dis. 2006, 42, 1351–1358. [Google Scholar] [CrossRef]
Diagnostics 14 00792 g001
Figure 1. (A) Colonies are circular, convex with entire margin, and mucoid. (B) Stretching of the K. pneumoniae colonies resulted in the formation of a string ≥5 mm in length, demonstrating the hypermucoviscous phenotype.
Figure 1. (A) Colonies are circular, convex with entire margin, and mucoid. (B) Stretching of the K. pneumoniae colonies resulted in the formation of a string ≥5 mm in length, demonstrating the hypermucoviscous phenotype.
Diagnostics 14 00792 g001
Diagnostics 14 00792 g002
Figure 2. Distributions of the hypermucoviscosity, aerobactin positivity, and community-acquired liver abscess of K. pneumoniae in this study group.
Figure 2. Distributions of the hypermucoviscosity, aerobactin positivity, and community-acquired liver abscess of K. pneumoniae in this study group.
Diagnostics 14 00792 g002
Table 1. Baseline characteristics and clinical presentations of Klebsiella pneumoniae isolates according to CLA.
Table 1. Baseline characteristics and clinical presentations of Klebsiella pneumoniae isolates according to CLA.
CLA (−) (n = 380)CLA (+) (n = 34)p Value
Epidemiology
   Male sex223 (58.7)25 (73.5)0.091
   Age (years)67.9 ± 13.666.6 ± 10.90.577
Underlying diseases
   Solid tumor115 (30.3)4 (11.8)0.022
   Chronic liver disease45 (11.8)5 (14.7)0.585
   Neurological disease162 (42.6)7 (20.6)0.012
   Chronic renal disease39 (10.3)0 (0.0)0.060
   Diabetes mellitus133 (35.0)13 (38.2)0.705
   Chronic lung disease40 (10.5)2 (5.9)0.558
   Solid-organ transplantation12 (3.2)0 (0.0)0.610
McCabe classification
   Nonfatal underlying disease282 (74.2)33 (97.1)0.004 *
   Ultimately fatal disease95 (25.0)1 (2.9)
   Fatal disease3 (0.8)0 (0.0)
Predisposing factors
   Urinary catheter184 (48.4)11 (32.4)0.072
   Percutaneous catheter drainage62 (16.3)26 (76.5)<0.001
   L-tube92 (24.2)2 (5.9)0.015
   Invasive procedure91 (23.9)26 (76.5)<0.001
   Recent operation72 (18.9)1 (2.9)0.019
   Prior ICU admission within 1 month55 (14.5)0 (0.0)0.014 *
Category of infection
   Community-acquired infection133 (35.0)34 (100.0)<0.001
   Healthcare-associated infection80 (21.1)0 (0.0)
   Nosocomial infection167 (43.9)0 (0.0)
Infection source
   Urinary tract infection88 (23.2)0 (0.0)0.002
   Intra-abdominal infection38 (10.0)34 (100.0)<0.001
   Respiratory infection163 (42.9)0 (0.0)<0.001
Clinical presentation
   Severe sepsis and septic shock125 (32.9)9 (26.5)0.443
   Metastatic infection4 (1.1)1 (2.9)0.351
   Concomitant bacteremia121 (31.8)21 (61.8)<0.001
   Mechanical ventilation64 (16.8)3 (8.8)0.224
   Admission to ICU100 (26.3)6 (17.6)0.267
Treatment outcomes
   Treatment failure (72 h)68 (17.9)2 (5.9)0.073
   Infection-related 30-day mortality42 (13.7)2 (10.0)1.000
   Acute kidney injury 46 (12.1)5 (14.7)0.592
Values are presented as mean ± standard deviation or number (%). * Fisher’s exact test. CLA: community-acquired liver abscess; ICU: intensive care unit.
Table 2. Antimicrobial resistance and microbiological characteristics of Klebsiella pneumoniae isolates according to CLA.
Table 2. Antimicrobial resistance and microbiological characteristics of Klebsiella pneumoniae isolates according to CLA.
CLA (−) (n = 380)CLA (+) (n = 34)p Value
Antimicrobial resistance rates
   Amikacin19 (5.0)0 (0.0)0.387
   Amoxicillin/clavulanate122 (32.1)1 (2.9)<0.001
   Aztreonam136 (35.8)1 (2.9)<0.001
   Cefazolin139 (36.6)1 (2.9)<0.001
   Cefepime134 (35.3)1 (2.9)<0.001
   Cefotaxime136 (35.8)1 (2.9)<0.001
   Ceftazidime136 (35.8)1 (2.9)<0.001
   Ciprofloxacin111 (29.2)0 (0.0)<0.001
   Ertapenem00n/a
   Gentamicin70 (18.4)2 (5.9)0.065
   Imipenem00n/a
   Piperacillin/tazobactam98 (25.8)2 (5.9)0.009
   Tigecycline43 (11.3)1 (2.9)0.156
   Trimethoprim/sulfamethoxazole101 (26.6)0 (0.0)<0.001
   ESBL positivity134 (35.3)1 (2.9)<0.001
Serotype
   K157 (15.0)20 (58.8)<0.001
   K250 (13.2)9 (26.5)0.042 *
   K53 (0.8)0 (0.0)1.000
   K2019 (5.0)0 (0.0)0.387
   K544 (1.1)0 (0.0)1.000
   K5716 (4.2)0 (0.0)0.383
   ND231 (60.8)5 (14.7)<0.001
Virulence gene
   rmpA137 (36.1)28 (82.4)<0.001
   magA47 (12.4)16 (47.1)<0.001
   allS62 (16.4)18 (52.9)<0.001
   mrkD370 (97.9)34 (100.0)1.000
   entB374 (98.9)34 (100.0)1.000
   kfu118 (31.2)20 (58.8)0.001
   Aerobactin143 (37.6)27 (79.4)<0.001
String test130 (34.2)25 (73.5)<0.001
Biofilm mass0.67 ± 0.460.98 ± 0.770.026
   >0.58 (median)177 (48.4)21 (61.8)0.135
   >0.80111 (30.3)18 (52.9)0.007
Values are presented as n (%) or mean ± standard deviation. * Fisher’s exact test. CLA: community-acquired liver abscess; n/a: not available; ESBL: extended-spectrum β-lactamase; ND: not detected.
Table 3. Significant virulence factors for community-acquired liver abscess in Klebsiella pneumoniae using logistic regression analysis.
Table 3. Significant virulence factors for community-acquired liver abscess in Klebsiella pneumoniae using logistic regression analysis.
VariableUnivariate AnalysisMultivariate Analysis
OR95% CIp ValueOR95% CIp Value
String test (+)5.342.42–11.78<0.001−−−
iutA (+)6.392.71–15.06<0.001−−−
rmpA (+)8.283.34–20.49<0.0015.832.15–15.780.001
magA (+)6.303.01–13.19<0.0012.341.01–5.400.047
allS (+)5.732.77–11.86<0.001−−−
kfu (+)3.151.54–6.450.002−−−
Biofilm > 0.802.581.27–5.250.0092.131.00–4.560.050
Multivariate logistic regression analysis was performed using the backward-conditional method for factors with p < 0.1 in the univariate logistic regression analysis. OR: odds ratio; CI: confidence interval.
Disclaimer/Publisher’s Note: The statements, opinions and data contained in all publications are solely those of the individual author(s) and contributor(s) and not of MDPI and/or the editor(s). MDPI and/or the editor(s) disclaim responsibility for any injury to people or property resulting from any ideas, methods, instructions or products referred to in the content.

Share and Cite

MDPI and ACS Style

Hyun, M.; Lee, J.Y.; Kim, H.A. Clinical and Microbiologic Analysis of Klebsiella pneumoniae Infection: Hypermucoviscosity, Virulence Factor, Genotype, and Antimicrobial Susceptibility. Diagnostics 2024, 14, 792. https://doi.org/10.3390/diagnostics14080792

AMA Style

Hyun M, Lee JY, Kim HA. Clinical and Microbiologic Analysis of Klebsiella pneumoniae Infection: Hypermucoviscosity, Virulence Factor, Genotype, and Antimicrobial Susceptibility. Diagnostics. 2024; 14(8):792. https://doi.org/10.3390/diagnostics14080792

Chicago/Turabian Style

Hyun, Miri, Ji Yeon Lee, and Hyun Ah Kim. 2024. "Clinical and Microbiologic Analysis of Klebsiella pneumoniae Infection: Hypermucoviscosity, Virulence Factor, Genotype, and Antimicrobial Susceptibility" Diagnostics 14, no. 8: 792. https://doi.org/10.3390/diagnostics14080792

Note that from the first issue of 2016, this journal uses article numbers instead of page numbers. See further details here.

Article Metrics

Back to TopTop