Search Results (9)

Klebsiella pneumoniae (K. pneumoniae, KP) is a significant opportunistic pathogen responsible for both nosocomial and community-acquired infections. Bacterial adhesion is the critical initial step for host colonization and the establishment of disease. In this study, we utilized a mariner transposon mutagenesis system to construct a mutant library from the clinical KP strain KP20, identifying a mutant with significantly impaired epithelial cell adhesion due to an insertion in the uspF gene. Genetic knockout experiments confirmed that uspF deletion markedly reduced the adhesion to human airway epithelial cells (Calu-3) and downregulated the transcription of type III pili-encoding genes (mrkABDF). Furthermore, uspF deficiency compromised antioxidant stress and serum resistance and increased susceptibility to dendritic cell and macrophage phagocytosis. In vivo challenge experiments further demonstrated that uspF deletion significantly attenuated K. pneumoniae virulence in mice. These findings provide important insights into the molecular pathogenesis of K. pneumoniae and identify UspF as a potential target for therapeutic intervention. Full article

Some bacterial species within the Enterobacteriaceae family possess different types of fimbrial (pili) adhesins that promote adherence to cells and colonization of host tissues. One of the well-characterized fimbrial systems is the pap operon, which encodes P fimbriae, a key virulence factor in urinary and systemic infections. One of the key regulators of P fimbriae is the transcriptional regulator PapB which plays a pivotal role as a master switch, not only by directing phase-variable expression of its own operon but also by influencing expression of heterologous fimbrial systems. This review explores the structural organization, biogenesis, and multi-tiered regulatory control of P fimbriae, with emphasis on PapB and homologous regulatory proteins such as SfaB, FocB, PixB, and PefB. Comparative genomics and phylogenetic analyses reveal that regulators belonging to the PapB family are evolutionarily conserved across π-fimbrial systems and also regulate other types of fimbriae. These regulators respond to epigenetic changes, host-derived signals, and global transcriptional cues to control levels of production of specific fimbriae in a bacterial population to dynamically modulate bacterial adhesion in different environmental niches. Optimally, understanding these mechanisms could lead to novel approaches to perturb PapB-family proteins and abrogate production of some types of fimbriae as a targeted strategy to prevent bacterial infections dependent on adherence mediated by PapB family regulators. Full article

This review explores the biofilm architecture and drug resistance of Enterococcus faecalis in clinical and environmental settings. The biofilm in E. faecalis is a heterogeneous, three-dimensional, mushroom-like or multilayered structure, characteristically forming diplococci or short chains interspersed with water channels for nutrient exchange and waste removal. Exopolysaccharides, proteins, lipids, and extracellular DNA create a protective matrix. Persister cells within the biofilm contribute to antibiotic resistance and survival. The heterogeneous architecture of the E. faecalis biofilm contains both dense clusters and loosely packed regions that vary in thickness, ranging from 10 to 100 µm, depending on the environmental conditions. The pathogenicity of the E. faecalis biofilm is mediated through complex interactions between genes and virulence factors such as DNA release, cytolysin, pili, secreted antigen A, and microbial surface components that recognize adhesive matrix molecules, often involving a key protein called enterococcal surface protein (Esp). Clinically, it is implicated in a range of nosocomial infections, including urinary tract infections, endocarditis, and surgical wound infections. The biofilm serves as a nidus for bacterial dissemination and as a reservoir for antimicrobial resistance. The effectiveness of first-line antibiotics (ampicillin, vancomycin, and aminoglycosides) is diminished due to reduced penetration, altered metabolism, increased tolerance, and intrinsic and acquired resistance. Alternative strategies for biofilm disruption, such as combination therapy (ampicillin with aminoglycosides), as well as newer approaches, including antimicrobial peptides, quorum-sensing inhibitors, and biofilm-disrupting agents (DNase or dispersin B), are also being explored to improve treatment outcomes. Environmentally, E. faecalis biofilms contribute to contamination in water systems, food production facilities, and healthcare environments. They persist in harsh conditions, facilitating the spread of multidrug-resistant strains and increasing the risk of transmission to humans and animals. Therefore, understanding the biofilm architecture and drug resistance is essential for developing effective strategies to mitigate their clinical and environmental impact. Full article

Background/Objectives: FimH adhesin, located at the tips of type 1 pili in Escherichia coli (E. coli), plays a crucial role in bacterial adhesion to the surface urothelial cells—a key step in the pathogenesis of urinary tract infections (UTIs). Given the rising concern over antimicrobial resistance (AMR), and considering that E. coli is one of the pathogens with the largest AMR burdens on a global scale, alternative strategies targeting bacterial adhesion are gaining increasing attention. Products that contain D-mannose and cranberry-derived phenolic compounds have shown promise in preventing E. coli colonization and infection. The aim of this study was to investigate the antiadhesive effects of cranberry-related phenolic compounds on FimH-mediated E. coli adhesion using a cellular hemagglutination inhibition assay, as well as to assess the synergistic effects of mannose and phenolic compounds on biofilm formation. Methods: A range of phenolic acids (benzoic, chlorogenic, hippuric, p-coumaric, ferulic and caffeic), resveratrol, (+)-catechin and procyanidin A, as well as a Vaccinium macrocarpon extract, were evaluated for their ability to inhibit FimH-mediated adhesion. A binocular microscope was used to observe agglutination, and we also evaluated the biofilm inhibition potential of the phenolic compounds in the presence of D-mannose. Results: Our results demonstrated that these compounds significantly reduced hemagglutination, with benzoic acid, chlorogenic acid, caffeic acid and resveratrol exhibiting strong inhibitory effects at concentrations as low as 0.25 mM. Furthermore, the addition of 1 mM solutions of these phenolic compounds to D-mannose resulted in a twofold reduction in the inhibition titer, suggesting synergistic interactions. In addition to their antiadhesive properties, the tested phenolic compounds contributed slightly to the inhibition of FimH-mediated biofilm formation, further supporting their potential roles in UTI prevention. Conclusions: These findings highlight the potential of cranberry-derived phenolics as natural antiadhesive agents against E. coli and warrant further investigation into their mechanisms of action and possible applications in infection control. Full article

Enterococcus species are known for their ability to form biofilms, which contributes to their survival in extreme environments and involvement in persistent bacterial infections, especially in the case of multi-drug-resistant strains. This review aims to provide a comprehensive understanding of the mechanisms underlying biofilm formation in clinically important species such as Enterococcus faecalis and the less studied but increasingly multi-drug-resistant Enterococcus faecium, and explores potential strategies for their eradication. Biofilm formation in Enterococcus involves a complex interplay of genes and virulence factors, including gelatinase, cytolysin, Secreted antigen A, pili, microbial surface components that recognize adhesive matrix molecules (MSCRAMMs), and DNA release. Quorum sensing, a process of intercellular communication, mediated by peptide pheromones such as Cob, Ccf, and Cpd, plays a crucial role in coordinating biofilm development by targeting gene expression and regulation. Additionally, the regulation of extracellular DNA (eDNA) release has emerged as a fundamental component in biofilm formation. In E. faecalis, the autolysin N-acetylglucosaminidase and proteases such as gelatinase and serin protease are key players in this process, influencing biofilm development and virulence. Targeting eDNA may offer a promising avenue for intervention in biofilm-producing E. faecalis infections. Overall, gaining insights into the intricate mechanisms of biofilm formation in Enterococcus may provide directions for anti-biofilm therapeutic research, with the purpose of reducing the burden of Enterococcus-associated infections. Full article

Uropathogenic Escherichia coli express hairlike proteinaceous surface projections, known as chaperone–usher pathway (CUP) pili. Type 1 pili are CUP pili with well-established pathogenic properties. The FimH adhesin subunit of type 1 pili plays a key role in the pathogenesis of urinary tract infections (UTIs) as it mediates the adhesion of the bacteria to urothelial cells of the bladder. In this study, two breast cancer cell lines, MDA-MB-231 and MCF-7, were used to demonstrate the cytotoxic activities of type 1 piliated uropathogenic E. coli UTI89 on breast cancer cells in a type 1 pili and FimH-mediated manner. E. coli were grown in static and shaking conditions to induce or inhibit optimal type 1 pili biogenesis, respectively. Deletion constructs of UTI89 ΔfimH and a complemented strain (UTI89 ΔfimH/pfimH) were further utilized to genetically assess the effect of type 1 pili and FimH on cancer cell viability. After incubation with the different strains, cytotoxicity was measured using trypan blue exclusion assays. UTI89 grown statically caused significant cytotoxicity in both breast cancer cell lines whereas cytotoxicity was reduced when the cells were incubated with bacteria grown under shaking conditions. The incubation of both MDA-MB-231 and MCF-7 with UTI89 Δfim operon or ΔfimH showed a significant reduction in cytotoxicity exerted by the bacterial strains, revealing that type 1 pili expression was necessary for cytotoxicity. Complementing the ΔfimH strain with pfimH reversed the phenotype, leading to a significant increase in cytotoxicity. Incubating type 1 pili expressing bacteria with the competitive FimH inhibitor D-mannose before cancer cell treatment also led to a significant reduction in cytotoxicity on both MDA-MB-231 and MCF-7 cancer cells, compared to vehicle control or D-mannose alone, indicating the requirement for functional FimH for cytotoxicity. Overall, our results reveal that, as opposed to UTI89 lacking type 1 pili, type 1 piliated UTI89 causes significant cancer cell mortality in a FimH-mediated manner, that is decreased with D-mannose. Full article

Streptococcus pneumoniae is a major cause of morbidity and mortality worldwide, and about 30% of the pneumococcal clinical isolates show type I pili-like structures. These long proteinaceous polymers extending from the bacterial surface are encoded by pilus islet 1 and play major roles in adhesion and host colonization. Pili expression is bistable and is controlled by the transcriptional activator RlrA. In this work, we demonstrate that the previously identified small noncoding RNA srn135 also participates in pilus regulation. Our findings show that srn135 is generated upon processing of the 5′-UTR region of rrgA messenger and its deletion prevents the synthesis of RrgA, the main pili adhesin. Moreover, overexpression of srn135 increases the expression of all pili genes and rises the percentage of piliated bacteria within a clonal population. This regulation is mediated by the stabilization of rlrA mRNA since higher levels of srn135 increase its half-life to 165%. Our findings suggest that srn135 has a dual role in pilus expression acting both in cis- (on the RrgA levels) and in trans- (modulating the levels of RlrA) and contributes to the delicate balance between pili expressing and non-expressing bacteria. Full article

Proficient crop production is needed to ensure the feeding of a growing global population. The association of bacteria with plants plays an important role in the health state of the plants contributing to the increase of agricultural production. Endophytic bacteria are ubiquitous in most plant species providing, in most cases, plant promotion properties. However, the knowledge on the genetic determinants involved in the colonization of plants by endophytic bacteria is still poorly understood. In this work we have used a genetic approach based on the construction of fliM, pilX and eps knockout mutants to show that the motility mediated by a functional flagellum and the pili type IV, and the adhesion modulated by exopolysaccarides are required for the efficient colonization of rice roots by the endophyte Azoarcus sp. CIB. Moreover, we have demonstrated that expression of an exogenous diguanylate cyclase or phophodiesterase, which causes either an increase or decrease of the intracellular levels of the second messenger cyclic di-GMP (c-di-GMP), respectively, leads to a reduction of the ability of Azoarcus sp. CIB to colonize rice plants. Here we present results demonstrating the unprecedented role of the universal second messenger cyclic-di-GMP in plant colonization by an endophytic bacterium, Azoarcus sp. CIB. These studies pave the way to further strategies to modulate the interaction of endophytes with their target plant hosts. Full article

Pseudomonas aeruginosa and Escherichia coli are the most prevalent Gram-negative biofilm forming medical device associated pathogens, particularly with respect to catheter associated urinary tract infections. In a similar manner to Gram-positive bacteria, Gram-negative biofilm formation is fundamentally determined by a series of steps outlined more fully in this review, namely adhesion, cellular aggregation, and the production of an extracellular polymeric matrix. More specifically this review will explore the biosynthesis and role of pili and flagella in Gram-negative adhesion and accumulation on surfaces in Pseudomonas aeruginosa and Escherichia coli. The process of biofilm maturation is compared and contrasted in both species, namely the production of the exopolysaccharides via the polysaccharide synthesis locus (Psl), pellicle Formation (Pel) and alginic acid synthesis in Pseudomonas aeruginosa, and UDP-4-amino-4-deoxy-l-arabinose and colonic acid synthesis in Escherichia coli. An emphasis is placed on the importance of the LuxR homologue sdiA; the luxS/autoinducer-II; an autoinducer-III/epinephrine/norepinephrine and indole mediated Quorum sensing systems in enabling Gram-negative bacteria to adapt to their environments. The majority of Gram-negative biofilms consist of polysaccharides of a simple sugar structure (either homo- or heteropolysaccharides) that provide an optimum environment for the survival and maturation of bacteria, allowing them to display increased resistance to antibiotics and predation. Full article