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Enterococcus faecalis cytolysin without effect on the intestinal growth of susceptible enterococci in mice
M M Huycke1, W A Joyce, M S Gilmore
1Medical and Research Services, VA Medical Center, University of Oklahoma Health Sciences Center, Oklahoma City 73104, USA.
Abstract:
A murine model was developed to determine whether the Enterococcus faecalis cytolysin, through its bacteriolytic action on gram-positive bacteria, could promote intestinal overgrowth of cytolytic strains. Sets of E. faecalis strains with varying cytolytic production and susceptibility to cytolytic activity were mixed 1:1 and allowed to compete in vitro in broth or in vivo after orogastric administration in mice pretreated with antibiotics. In general, cytolytic strains outgrew, by as much as 2000-fold, competing cytolysin-susceptible or -hypersusceptible strains in vitro. In contrast, no growth advantage was observed in vivo, despite similar transient colonization of the murine intestinal tract by both cytolytic and cytolysin-susceptible strains. These data suggest that cytolysin plays little role in promoting intestinal overgrowth of enterococci through bacteriolytic activity.
Insights
Enterococcus faecalis cytolysin, which lyses bacteria, did not promote overgrowth of cytolytic strains in mouse intestines. In vitro, cytolytic strains outcompeted susceptible ones, but this effect was not seen in vivo.
Area of Science:
- Microbiology
- Gastroenterology
- Bacterial Pathogenesis
Background:
- Enterococcus faecalis is an opportunistic pathogen.
- The E. faecalis cytolysin (Efc) is a pore-forming toxin with bacteriolytic activity against Gram-positive bacteria.
- The role of Efc in promoting E. faecalis intestinal overgrowth is not well understood.
Purpose of the Study:
- To investigate whether the bacteriolytic action of E. faecalis cytolysin promotes intestinal overgrowth of cytolytic strains.
- To compare the competitive fitness of cytolytic and cytolysin-susceptible E. faecalis strains in vitro and in vivo.
Main Methods:
- A murine model was utilized, with mice pretreated with antibiotics to disrupt the native microbiota.
- Sets of E. faecalis strains with varying cytolytic production and susceptibility were competed in vitro in broth and in vivo after orogastric administration.
- Bacterial populations were quantified to assess competitive growth.
Main Results:
- In vitro, cytolytic E. faecalis strains outgrew cytolysin-susceptible or hypersusceptible strains by up to 2000-fold.
- In vivo, no significant growth advantage was observed for cytolytic strains compared to susceptible strains.
- Both cytolytic and cytolysin-susceptible strains showed similar transient colonization of the murine intestinal tract.
Conclusions:
- The bacteriolytic activity of E. faecalis cytolysin does not appear to confer a growth advantage to cytolytic strains within the murine intestinal environment.
- The in vitro observation of competitive exclusion is not replicated in vivo, suggesting host or microbiota factors modulate Efc's role.
- Cytolysin likely plays a minimal role in promoting intestinal overgrowth of enterococci through its bacteriolytic mechanism.