Investigating the type VII secretion system of Enterococcus faecalis in competition with Pseudomonas aeruginosa

Abstract

Enterococcus faecalis and Pseudomonas aeruginosa are opportunistic bacterial pathogens commonly co-isolated from polymicrobial wound, gum and urinary tract infections. In polymicrobial environments, bacterial secretion systems are indispensable for nutrient acquisition, stress response and bacterial interactions. Both the E. faecalis Type VII secretion system (T7SS) and P. aeruginosa Type VI secretion system (T6SS) have demonstrated antagonism within their respective ecological niches (P. aeruginosa T6SS against other Gram-negative bacteria, and E. faecalis T7SS against other Gram-positive bacteria) during interbacterial competition. Despite their co-prevalence, there is limited understanding on whether E. faecalis T7SS and P. aeruginosa T6SS contribute to competitive interactions during co-culture. Here, we assess conditions in which the T7SS is upregulated and whether it has an impact on P. aeruginosa. Through RT-qPCR, we show that E. faecalis T7SS genes are upregulated when cultured in glucose, mannose and galactose. We also demonstrate that while E. faecalis T7SS genes remain upregulated in mannose-supplemented conditions, E. faecalis does not inhibit P. aeruginosa growth during co-culture. Similarly, P. aeruginosa T6SS activity does not affect E. faecalis growth in co-culture. Collectively, our findings suggest mutual resistance between E. faecalis and P. aeruginosa that is independent of their respective T7SS and T6SS.