Mechanisms of enterococcus faecalis pathogenesis in wound infection
Chong, Kelvin Kian Long
Date of Issue2018-12-31
Interdisciplinary Graduate School (IGS)
Singapore Centre for Environmental Life Sciences Engineering
Enterococci are among the most prevalent pathogens isolated from wound infections, and Enterococcus faecalis is typically in the top four most commonly isolated bacterial species in diabetic wounds. Despite its prevalence, very little is known about the pathogenic mechanisms of E. faecalis in wound infections. Our overall aim was to identify E. faecalis fitness factors in wounds and to understand the host-pathogen interplay that promotes infection. To achieve this aim, we established a mouse E. faecalis wound infection model to study its infection dynamics. High titer E. faecalis inocula into wounds resulted in acute bacterial replication with a concomitant pro-inflammatory neutrophilic response, followed by a reduction in bacterial burden that can persist within wounds with limited inflammation. To better understand the bacterial factors that contribute to chronic E. faecalis wounds, we collected 49 E. faecalis isolates from a variety of infected human wounds and performed comparative genomics. We found that E. faecalis wound isolates were predominantly clustered in ST16/179 and CC2/6. Isolates with the greatest in vitro biofilm-forming capacity correlated with the presence of ecbA, a putative cell wall surface anchor family protein that binds to collagen type V and fibrinogen, suggesting it may be a potential indicator of high biofilm formation in vivo. To elucidate additional E. faecalis wound fitness factors, we performed transposon sequencing and also tested E. faecalis mutants in a hypothesis-driven manner. We found that E. faecalis MprF, which confers resistance to cationic peptides, and a phosphotransferase system are required for E. faecalis persistence in wounds. In E. faecalis polymicrobial wound infections with S. aureus, we observed that E. faecalis can augment biofilm formation and titers, possibly through utilization of S. aureus-derived L-arginine. Together, these findings suggest that E. faecalis can both modulate the host immune response and tune its metabolism during monomicrobial and polymicrobial infections to mediate its persistence in wounds.