Leptospira interrogans, the agent of leptospirosis, employs complex virulence mechanisms that are not fully understood at a systems level. To elucidate the regulatory landscape of its pathogenicity, we used Weighted Gene Co-expression Network Analysis (WGCNA) on a comprehensive transcriptomic dataset to map the architecture of its virulence programs. Our analysis revealed that the L. interrogans transcriptome is organized into distinct, functionally coherent modules. We discovered that known virulence factors are significantly concentrated in two key modules: a "lightgrey" module that orchestrates host colonization and immune evasion, containing genes for surface adhesion (loa22, ompL1) and defense (lipL21); and a "black" module that functions as an arsenal for tissue invasion (colA), stress adaptation (clpB), and cytotoxicity (sph2). Furthermore, by contextualizing genes within this network, our approach implicated numerous uncharacterized genes (e.g., from the PF07598 family) in pathogenesis due to their strong co-expression with established virulence factors. These findings provide a systems-level blueprint of the regulatory networks driving leptospirosis, offering a rich resource of functionally validated gene modules and novel targets for the development of next-generation vaccines and therapeutics. These findings not only deepen the understanding of L. interrogans virulence regulation but also provide a conceptual framework for integrating transcriptomic data into systems-level models of bacterial pathogenesis, paving the way for translational applications in diagnostics and vaccine design.
A marked difference in virulence was observed between two subpopulations of the Edwardsiella piscicida FSW910410 strain, originally isolated from olive flounder (Paralichthys olivaceus). While the strain maintained under routine laboratory culture conditions retained high virulence, the same strain stored long-term at -80 °C lost its ability to induce disease in olive flounder. Comparative in vivo assays demonstrated complete avirulence in the frozen-stored subpopulation, contrasting with high mortality rates induced by the virulent counterpart. Despite over 99 % genomic sequence identity and identical virulence gene repertoires, the two subpopulations differed significantly in their ability to evade host immune responses. Whole-genome methylation profiling revealed comparable levels of N6-methyladenine (m6A) but notably reduced levels of cytosine methylation (m4C/m5C) in the avirulent subpopulation, particularly in genes associated with type III and type VI secretion systems (T3SS and T6SS). Quantitative RT-PCR analyses confirmed substantially lower expression of T3SS and T6SS genes in the avirulent strain. These results suggest that epigenetic modifications, especially cytosine methylation, may contribute to the observed differences in virulence, although additional regulatory mechanisms cannot be excluded. Collectively, the data highlight the complex interplay of genomic and epigenetic factors that may influence bacterial pathogenicity during prolonged storage or passage.
Klebsiella pneumoniae is a Gram-negative bacterium and an important pathogen implicated in both hospital- and community-acquired pneumonia. K. pneumoniae strains are either classical, hypervirulent (hvKp), or antibiotic-resistant. There are several virulence factors of K. pneumoniae that helps immune evasion and survivability within the host. This review emphasizes the host immune interactions of K. pneumoniae. Evasion strategies of the pathogen and complex risk factors of the infection have been explained. Different diagnostic approaches, such as computed tomography, PCR, and Lateral Flow Immunoassay (LF), have been used for the diagnosis of K. pneumoniae. Multidrug-resistant Klebsiella pneumoniae (MDRKP) has emerged as a significant global public health concern, with higher cases of carbapenem-resistant K. pneumoniae (CRKP). CRKP caused more than 7000 deaths annually in Europe. Although K.pneumoniae has several mechanisms of antibiotic resistance, resistance to β-lactams, specifically carbapenems, causes a notable difference. Newer β-lactam/β-lactamase inhibitor combinations, such as ceftazidime-avibactam and cefiderocol are preferred for KPC-producing infections. This review emphasizes the ongoing challenges in translating therapeutic advancements into successful clinical outcomes, as well as the persisting complications in K. pneumoniae research, including the unsolved differences between hypervirulent and classical strains. Alternative methods, including bacteriophage therapy, antimicrobial peptides, and immunotherapy, are being studied for tackling CRKP. This review addresses recent advances in understanding Klebsiella pneumoniae-induced pneumonia, emphasizing how virulence factors interact with immune defences. Additionally, we highlight key challenges in antimicrobial resistance, current therapeutic strategies, K. pneumoniae's implications for infection control and antibiotic stewardship. Overall, this review aims to contribute to a deeper understanding of K. pneumoniae and to guide future interventions for effective prevention, control, and treatment strategies.
Pseudomonas aeruginosa can exploit its metabolic flexibility during cystic fibrosis lung infections to reduce antibiotic sensitivity and offset resistance costs, traits that influence its evolutionary trajectory. Although both traits are linked to nutrient conditions, their role in resistance evolution remains poorly defined. We examined how single-nutrient conditions influence resistance evolution in P. aeruginosa through phenotypic and genotypic adaptations after adaptive laboratory evolution with different antibiotics in single-nutrient media. Antibiotic susceptibility testing showed limited MIC differences for ceftazidime and imipenem, but stronger effects for ciprofloxacin, colistin, and tobramycin. Ciprofloxacin evolution in glutamate medium yielded the highest MIC increase, with at least a 4-fold rise, whereas tobramycin evolution in glucose resulted in up to a 4-fold MIC reduction compared to lineages evolved under all other nutrient conditions for the same antibiotic. Whole-genome sequencing showed nutrient-specific mutation in wbpL after tobramycin evolution in glucose, and fusA and pmrB across conditions. Ciprofloxacin resistance in glutamate-lineages involved yicC, whereas nfxB mutations were absent in glucose- and arginine-evolved lineages. No distinct nutrient-specific differences were seen for colistin. These findings underscore the significant role of nutrient conditions in shaping resistance and highlight the need to consider physiologically relevant media when studying antibiotic resistance evolution.
PURPOSE:This study aimed to evaluate the role of membrane microdomains (MMd) in virulence of Bacillus anthracis by assessing the effects of known antifungal compounds, referred to as raft-associated lipid biosynthesis inhibitors (RALBIs), on its pathophysiology. MATERIALS AND METHODS:FDA-approved antifungal compounds representing three distinct classes-azoles (ketoconazole), allylamines (terbinafine), and polyenes (nystatin), were tested against B. anthracis. These compounds target different enzymes involved in MMd-associated lipid biosynthesis. Their impact on sporulation, toxin secretion, macrophage interaction, bio-signaling, cell envelope fluidity, and biofilm formation was examined. Additionally, their synergistic potential with conventional antibiotics was evaluated. RESULTS:RALBIs markedly attenuated the pathogenic traits of B. anthracis, including reduced macrophage association, diminished toxin secretion, and impaired sporulation. Treatment also altered growth kinetics, morphology, biofilm development and cell envelope fluidity. Importantly, the combination of RALBIs with erythromycin significantly reduced its minimum inhibitory concentration (MIC) against B. anthracis. CONCLUSION:These findings highlight membrane microdomains as crucial regulators of virulence in B. anthracis and identify RALBIs as promising adjunctive agents. By targeting MMd, sterol inhibitors disrupt multiple pathogenic pathways and enhance antibiotic efficacy, underscoring their potential as novel antibacterial strategies.
