Relative contributions of Enterococcus faecalis OG1RF sortase-encoding genes, srtA and bps (srtC), to Biofilm formation and a murine model of urinary tract infection

Deletion mutants of the two sortase genes of Enterococcus faecalis OG1RF were constructed. srtC (renamed here bps for biofilm and pilus-associated sortase) was previously shown to be necessary for the production of Ebp pili and important for biofilm formation and endocarditis. Here, we report that a srtA deletion mutant showed a small (5%) yet significant (P = 0.037) reduction in biofilm relative to OG1RF, while a Delta srtA Delta bps double mutant showed a much greater reduction (74% versus OG1RF and 44% versus the Delta bps mutant). In a murine urinary tract infection (UTI), the 50% infective doses of both the Delta srtA Delta bps and Delta bps mutants were similar to 2 log(10) greater than that of OG1RF or the Delta srtA mutant. Similarly, similar to 2 log(10) fewer bacteria were recovered from the kidneys after infection with the Abps mutant (P = 0.017) and the Delta srtA Abps double mutant (P = 0.022) compared to wild-type strain OG1RF. In a competition UTI, the Abps mutant was slightly, but not significantly, less attenuated than the Delta srtA Abps double mutant. Fluorescence-activated cell sorter analysis with Ebp-specific antibodies confirmed that a minority of OG1RF cells express Ebp pili on their surface in vitro and that Bps has a major role in Ebp pilus biogenesis but also indicated a function for SrtA in surface localization of the pilus subunit protein EbpA. In conclusion, deletion of bps had a major effect on virulence in murine UTIs, as well as biofilm; deletion of srtA from OG1RF had little effect on these phenotypes, but its deletion from a bps mutant had a pronounced effect on biofilm, suggesting that Bps and/or the proteins it anchors may compensate for the loss of some SrtA function(s).