*3.2. Vulvovaginal Candidiasis*

The exact association between DM and vulvovaginal candidiasis (VVC) remains to be clarified, but some investigations propose that the general reduced immune response associated with DM is the main cause of recurrent VVC [218–221]. Additionally, diabetes type, severity, and degree of glucose control are probable risk factors associated with VVC prevalence, and it is acknowledged that the metabolic disorders that predispose to clinical vaginitis can be reduced by performing an appropriate diabetic control [222,223]. *C. albicans* is the most common species isolated, followed by *C. glabrata* in patients both with and without diabetes [219,224,225]. Studies have been reporting an increased frequency of infection by NCAC over time [226,227], especially *C. glabrata*, which is more recurrently associated with VVC in African and Asian countries [228–231]. Table 2 summarizes the metabolic disorders that can predispose one to VVC and those that can be decreased with proper diabetic control.

Several studies explored the association between VVC and DM. Gunther et al. [232] investigated the frequency of total isolation of vaginal *Candida* sp. and its different clinical profiles in women with type 2 DM compared to non-diabetic women in Brazil [232]. Vaginal yeas<sup>t</sup> isolation occurred in 18.8% in the diabetic group and in 11.8% of women in the control group. The diabetic group was shown to be more symptomatic (VVC + recurrent VVC (RVVC) = 66.66%) than colonized women (33.33%), and indicated more colonization, VVC, and RVVC than the controls. Sherry et al. [233] studied the epidemiology of VVC in a cohort in order to find the causative organisms associated with VVC. The authors noticed a shifting prevalence of *Candida* sp. with *C. albicans* as the most common yeas<sup>t</sup> but an increase of NCAC. A heterogeneous biofilm-forming capacity associated with lower antifungal drug sensitivity was also reported.

On the contrary, Ray et al. [234] stated that out of 11 diabetic patients, *C. glabrata* was isolated in 61.3% and *C. albicans* in 28.8% of VVC cases [234]. Other studies have shown similar results in diabetic women [221,235,236]. Results showed a persistent vaginal colonization with *C. glabrata* in estrogenized streptozotocin-induced type 1 diabetic mice, and vaginal polymorphonuclear (PMN) infiltration (constantly low) was found in a murine model study by Nash and colleagues [237]. Contrary to what happens in women and in other in vivo studies, in this case, curiously, biofilm formation was not detected, and co-infection of *C. glabrata* with *C. albicans* did not induce synergistic immunopathogenic effects [237].


**Table 2.** Physiopathology and etiology related to the occurrence of vulvovaginitis in diabetics.


**Table 2.** *Cont.*

In a different study, Nyirjesy and colleagues evaluated the effects of sodium glucose co-transporter 2 inhibitors (e.g., canagliflozin, dapagliflozin, sitagliptin) used for the treatment of type 2 DM. These drugs improve glycemic control by increasing urinary glucose excretion and are related to increased vaginal colonization with *Candida* sp. and in VVC adverse events in women with type 2 DM [252]. Of the nine subjects with VVC with a positive vaginal culture at the time of the adverse event, six cultures were positive for *C. albicans*, only one was positive for *C. glabrata*, and one was positive for *C. tropicalis*. These findings confirm previous suggestions that *C. glabrata* is less pathogenic than *C. albicans* and more often associated with asymptomatic colonization in VVC [261]. The investigation theorized that urinary glucose excretion and the subsequent deposition of urine on the vulvovaginal tissues with voiding are more significant factors in increasing the risk of VVC in diabetic women than overall glycemic control. In this study, women showed improved glycemic control due to the administration of canagliflozin [262,263] with a higher prevalence of *Candida* sp. colonization and symptomatic infection, which was also detected with dapaglifozin [264]. Also related to SGLT2 inhibitors, the prevalence and risk of VVC before SGLT2 inhibitors was carefully evaluated in real-world practice by Yokoyama and colleagues [265]. They reported that before starting SGLT2 inhibitors, 14.9% of the participants had positive vaginal *Candida* sp. colonization. Younger age and the presence of microangiopathy were significantly associated with the colonization. Moreover, of the 65 participants who were negative for *Candida* sp., 24 participants (36.9%) converted to a positive culture, and 18 participants (15.8%) developed symptomatic vaginitis. The authors concluded that the rates of developing positive colonization and symptomatic vaginitis after starting SGLT2 inhibitors appear to be higher in real-world practice than the rates of 31% and 5–10% in clinical trials, respectively. Risk factors of vaginal *Candida* colonization might be different before and after taking SGLT2 inhibitors [265].

The colonization of the vagina in prepubertal girls with *Candida* sp. is rare, as the low estrogen levels during childhood result in a rich anaerobic vaginal flora which inhibits *Candida* sp. Growth [266,267]. In a recent report, Atabek et al. [219] isolated *Candida* sp. in 39% of children with type 1 DM between 8–16 years in age. The subjects who had *Candida* sp. colonization and candidiasis were considered all acute. *C. albicans* was found in 50% of all cases, followed by *C. glabrata* (36.6%), *C. krusei* (3.3%), and *C. dubliniensis* (3.3%). Patients with VVC had a greater mean HbA1c when compared to those without such infections, and the authors thus suggested that patients with DM should undergo periodic screening for genital candidiasis [219]. Similarly, Sonck et al. [268] studied the anogenital yeas<sup>t</sup> flora of 166 diabetic girls of less than 15 years of age with vulvitis, revealing that 55% were colonized, mostly by *C. albicans*.

Numerous studies have described the higher prevalence of asymptomatic vaginal colonization and symptomatic infection with *Candida* sp. in diabetic women, and some studies sugges<sup>t</sup> pregnancy as an additional risk factor [254–256], although results are inconsistent [28,226].

Several studies have also shown that pregnancy and uncontrolled diabetes increase the infection risk. It is likely that reproductive hormone fluctuations during pregnancy and elevated glucose levels

characteristic of diabetes provide the carbon needed for *Candida* overgrowth and infection. However, Sopian IL et al. [269] showed no relationship between diabetes and the occurrence of vaginal yeas<sup>t</sup> infection in pregnan<sup>t</sup> women, showing that there was no significant association between infection and age group, race, or education level [269]. In another report, Zheng et al. [254] studied the diversity of the vaginal fungal flora in healthy non-pregnan<sup>t</sup> women, healthy pregnan<sup>t</sup> women, women with gestational DM, and pregnan<sup>t</sup> women with DM type 1 through an 18S rRNA gene clone library method [254]. Results showed that the most predominant vaginal fungal species belonged to the *Candida* and *Saccharomyces* genera. In a study of 251 women, Nowakowska et al. [270] demonstrated that the probability of vaginal mycosis was 4-fold greater in type 1 DM patients and nearly 2-fold greater in those with gestational DM when compared to healthy pregnan<sup>t</sup> women. The report also highlighted the predominant role of poor glycemic control in the increased prevalence of vaginal candidiasis in pregnan<sup>t</sup> women with type 1 DM [270]. In 2011, Masri et al. [271] determined the prevalence of *Candida* sp. in vaginal swabs of pregnan<sup>t</sup> women from Serdang Hospital, Selangor, Malaysia, and their antifungal susceptibility. Results showed that 17.2% of the specimens were *Candida* sp., with *C. albicans* being the most common species detected (83.5%), followed by *C. glabrata* (16%) and *C. famata* (0.05%). All *C. albicans* and *C. famata* isolates were susceptible to fluconazole, whereas *C. glabrata* isolates had a dose-dependent susceptibility. The authors concluded that the first trimester, the second trimester, and DM were significant risk factors in patients for the vaginal candidiasis (*p* < 0.001). However, other studies noted that DM or impaired glucose tolerance during pregnancy was not connected with vaginal candidiasis [256]. Bassyouni et al. [242] explored the prevalence of VVC in diabetic women versus non-diabetic women and compared the ability of identified *Candida* sp. isolates to secrete PL and SAPs with the characterization of their genetic profile. The study involved 80 females with type 2 DM and 100 non-diabetics within the child-bearing period. Results revealed that VVC was significantly higher among the diabetic group (50%) versus the non-diabetic group (20%), and *C. albicans* was the predominant species in both groups (75% in non-diabetics and 50% in diabetics), followed by *C. glabrata* (20% in non-diabetics and 42.5% in diabetics). They also found that *Candida* sp. isolated from diabetics secreted higher quantities of proteinase than non-diabetics (87.7% and 65%, respectively), especially for *C. albicans* and *C. glabrata*, but non-significant associations between any of the tested proteinase or PL genes and DM were detected. These results were—by some means—in agreemen<sup>t</sup> with the ones from other reports [243,244] that also detected *C. parapsilosis* and *C. tropicalis* in a group of diabetic women. Kumari et al. [248] detected poor PL production in the isolated *Candida* sp. (causing vulvovaginitis), of which 81.25% were *C. parapsilosis*, 30.43% *C. albicans*, and 18.75% *C. glabrata*. Moreover, insignificant differences in the expression of *Candida* sp. *PLB1-2* genes and *SAP1–SAP8* genes between diabetic and non-diabetic women were reported by Bassyouni and colleagues [242]. Still, they concluded that the higher prevalence of VVC among diabetics could be directly correlated to increased SAPs production. The discrepancies between the results of different reports may be due to changes in growth conditions and host factors that alter the gene expression qualitatively and quantitatively [59,247], although findings sugges<sup>t</sup> that the expression of hydrolytic enzymes by *Candida* sp. is a multifactorial process in patients with DM and the hyperglycemia level is thus not the only implicated factor.

Lastly, VVC is intimately related to vaginal mucosae biofilms. Mikamo and colleagues studied the involvement of *Candida*'s complement receptor (ICAM-1) in the adhesion of *C. albicans* or *C. glabrata* to the genitourinary epithelial cells in high glucose states. Their results demonstrated that, while the adhesion of *C. albicans* to human vaginal epithelial cells VK2/E6E7 significantly increased in the high glucose, human vulvovaginal epidermal cells A431 did not. ICAM-1 expression was increased in VK2/E6E7 cultured in the high glucose, but the expression level in A431 was not elevated. These data suggested that ICAM-1 is a ligand in the adhesion of *C. albicans* to the vaginal epithelial cells in an environment with high glucose concentration. Moreover, both host immune dysfunction and the adjustment in epithelial cells were considered responsible for VVC in diabetic patients [272].

#### *3.3. Urinary Tract Candidiasis*

Around 10% to 15% of in-hospital urinary tract infections (UTIs) are related to *Candida* sp. and the prevalence is still increasing [273]. Some predisposing factors such as DM, urinary retention, urinary stasis, renal transplantation, and hospitalization can increase the risk of candiduria. Specifically, DM has been known to cause severe complicated UTIs as a result of its various changes in the genitourinary system [274]. Since the 1980s, there has been a marked increase in opportunistic fungal infections involving the urinary tract, of which *C. albicans* is the most commonly isolated species, but NCAC sp. is now the majority in many countries worldwide [275,276]. Candiduria (presence of *Candida* sp. in urine) is an increasingly common finding in hospitalized patients [14], and subjects with DM are at a higher risk of developing fungal UTIs. Thus, reducing risk factors such as increasing glycemic control and the removal of urinary catheters can result in the remission of candiduria [273]. Physiopathology and etiology related to the occurrence of UTIs related to *Candida* sp. and DM are presented in Table 3.

According to the results of the Falahati et al. [277] study, there were significant associations between candiduria and the female gender, high fasting blood sugar and urine glucose, uncontrolled diabetes (HbA1c ≥ 8), and acidic urine pH (*p* < 0.05)**.** Causative agents were identified as *C. glabrata* (n = 19, 50%), *C. albicans* (n = 12, 31.6%), *C. krusei* (n=4, 10.5%), *C. tropicalis* (n = 2, 5.3%), and *C. kefyr* (n=1, 2.6%). The study concluded that when considering the high incidence rate of candiduria in diabetic patients, the control of diabetes, predisposing factors, and causal relationships between diabetes and candiduria should be highlighted [277]. In a 2018 study, Esmailzadeh et al. [276] evaluated candiduria among type 2 diabetic patients. Indeed, the results showed that the rate of candiduria was relatively high in type 2 diabetic patients and they were also suffering from a lack of proper blood glucose control. Although the frequency of NCAC sp. was not significantly higher than *C. albicans*, they obtained more from those with symptomatic candiduria [276]. In a cross-sectional study, Yismaw et al. [273] determined the fungal causative agents of UTIs in asymptomatic and symptomatic diabetic patients and associated risk factors. Significant candiduria was detected in 7.5% and 17.1% of asymptomatic and symptomatic type 2 diabetic patients, respectively. Among the isolated *Candida* sp., 84.2% was observed in the asymptomatic diabetic patients and the remaining 15.8% in symptomatic patients. Rizzi and Trevisan studied the prevalence and significance of UTIs and genital infections (GI) in diabetes and the effects of sodium glucose cotransporter 2 (SGLT-2) inhibitors on these complications. Results presented that diabetic patients are at high risk of UTIs and of GIs. The authors concluded that only GIs were associated with poor glycemic control. Although patients treated with SGLT-2 inhibitors have an increased 3–5 fold risk of GIs, proper medical education may reduce this risk [278].

Diabetes mellitus, indwelling bladder catheter, sex (female), and the use of antibacterial agents have been found as the risk factors identified for both *C. glabrata* and *C. albicans* candiduria [275], as previously reported [27,279]. Emphysematous cystitis, which almost exclusively occurs in diabetic patients, is rare and is seldom the result of a fungal infection [280,281]. This condition is associated with a gas formation that may present itself as cystitis, pyelitis, or pyelonephritis. Uncontrolled DM is a major risk factor for this type of infection, as it provides a favorable microenvironment in which the gas-forming organisms can grow [282,283]. Alansari et al. [284] reported a case in which a patient with uncontrolled DM was diagnosed with emphysematous pyelitis by *C. tropicalis*, while Wang et al. [285] also reported the case of a 53-year-old male patient with fungus ball and emphysematous cystitis caused concurrently by *C. tropicalis*. The predisposing factors were DM and usage of broad-spectrum antibiotics. Garg et al. [286], in a one-year prospective single center study at Dayanand Medical College and Hospital, observed 151 diabetic and non-diabetic female patients diagnosed with UTIs. Uncontrolled diabetes was more commonly associated with severe UTIs like pyelonephritis and emphysematous pyelonephritis.

**Table 3.** Physiopathology and etiology related to the occurrence of urinary tract infections and systemic candidiasis in diabetics.


*Escherichia coli* was the most frequently isolated species in both groups, followed by *Klebsiella*, *Pseudomonas*, and *Candida* sp., and the latter was only isolated from the diabetic population. Tumbarello et al. [288] identified DM and urinary catheterization as features that are specifically associated with biofilm-forming *Candida* sp. bloodstream infections. Later, Vaidyanathan et al. [281] related a case of a 58-year-old diabetic paraplegic male with a long-term indwelling urethral catheter that developed a catheter block. Results showed an *E. coli* and *C. albicans* co-infection and HbA1c (glycosylated haemoglobin) was 111 mmol/mol, which is associated with uncontrolled DM. *C. albicans* later disseminated into the bloodstream through the damaged bladder and the urethral mucosa. Moreover, those isolates formed consistently high levels of biofilm formation in vitro and a resistance to voriconazole was also detected [281]. In another report, Suzuki et al. [287] investigated the relationship between UTIs and glucosuria, observing the effect of glucosuria induced by sodium-glucose cotransporter 2 (SGLT2) inhibitors on the progression of UTIs in mice. The results showed that in mice treated with dapagliflozin and canagliflozin (not tofogliflozin), the amount of *C. albicans* colony forming units (CFU) in kidneys increased in accordance with both treatment duration and dosage. The urine glucose concentration (UGC) significantly increased up to 12 (tofogliflozin) to 24 h (dapagliflozin and canagliflozin) after SGLT2 administration, indicating that a greater susceptibility to UTIs is associated with a persistent increase in UGC [287].
