Determinants of enterococcal cholic acid resistance identified by TnSeq

Enterococcus faecalis is a common commensal bacterium in animal gastrointestinal (GI) tracts and a leading cause of opportunistic infections of humans in healthcare settings. Despite the pathogenic potential of enterococci in susceptible patients, our understanding of normal enterococcal ecology and the genetic basis for persistence in the GI tract of healthy individuals is limited. To colonize and thrive in the GI tract, E. faecalis must withstand harsh physiochemical conditions, including the presence of bile salts. Therefore, we used transposon sequencing (TnSeq) to interrogate the genome of E. faecalis OG1RF for resistance determinants to cholic acid. E. faecalis OG1RF is a plasmid-free strain that contains few mobile elements yet retains the robust survival characteristics, intrinsic antibiotic resistance, and virulence traits characteristic of most E. faecalis genotypes. We created a minimal input pool containing 6,829 Tn mutants chosen for maximal genomic coverage and used an approach we term SMarT (Sequence-defined Mariner Technology) TnSeq to identify genetic determinants of bile resistance in E. faecalis OG1RF. These included several genes previously associated with bile acid resistance as well as new loci.