Studying mechanisms of bile resistance in Shigella flexneri
Embargo Date
2027-09-23
OA Version
Citation
Abstract
The Shigella species, a group of pathogenic Gram-negative enteric bacteria, are the causative agent of shigellosis or bacillary dysentery. The infection affects millions worldwide each year and manifests as watery or bloody diarrhea, with fever, cramping, and dehydration. The emergence of multidrug-resistant strains has significantly elevated mortality rates, particularly impacting vulnerable populations such as children under five years of age, immunocompromised individuals, and the elderly in developing regions. Recent outbreaks throughout North America and Europe have further worsened infection rates. Consequently, therapeutic interventions against Shigella represent a critical area of investigation to mitigate the global disease burden. Despite substantial research efforts and understanding key concepts in infection, no approved vaccine has yet been developed. Further elucidation of pathogenic mechanisms in Shigella is imperative to advancing vaccine development. The gastrointestinal environment encountered by Shigella during host transit profoundly influences pathogenesis and subsequent infection dynamics. Within the gastrointestinal tract, Shigella confronts not only abundant nutrition but also hosts innate defenses, including bile, an essential component for digestion with bactericidal properties. Composed primarily of bile salts, this initial stressor induces key pathoadaptation in Shigella, including bile salt resistance and changes in gene expression that enhance pathogenesis and, ultimately, infection in the colon. To facilitate bile salts resistance, Shigella modulates its lipopolysaccharide (LPS) structure expressed on the outer surface of the bacterial cell. Composed primarily of main regions: a transmembrane lipid (lipid A), a polysaccharide core, and an O-antigen of repeating motifs that extend into the extracellular space. This study aimed to elucidate the role of LPS in contributing to bile salts resistance and investigate how bile salts affect LPS structure under diverse nutritional environments.
Using Shigella flexneri serotype 2a strain 2457T in both wild-type (WT) and LPS mutant (∆galU) forms, we studied the roles of the LPS polysaccharide core and O-antigen in bacterial growth and resistance to bile salts. We also examined LPS modifications when bacteria were exposed to bile salts and varying nutritional conditions by extracting LPS from bacterial cultures and analyzing these extracts by Sodium Dodecyl Sulfate Polyacrylamide Gel Electrophoresis (SDS-PAGE). The growth curve analyses revealed that exposure to bile salts decreased bacterial growth, particularly for the ∆galU mutant that lacks the O-antigen, while the addition of glucose reduced the impact of bile salts exposure. Our findings from the LPS extractions indicate that exposure to bile salts, alone or in combination with glucose, differentially affected various components of the LPS structure and confirmed the importance of the O-antigen in facilitating bile salts resistance. Previous studies have proven that LPS confers bile resistance to Shigella and that the LPS formation and structure vary according to the different amounts of bile salts they are exposed to. This study enhances our understanding of how LPS contributes to bile salts resistance in S. flexneri, potentially informing efforts to develop an effective vaccine against this pathogen.
Description
2024