Comparative genomic analysis reveals significant enrichment of mobile genetic elements and genes encoding surface structure-proteins in hospital-associated clonal complex 2 Enterococcus faecalis

In the present study, we have used a comparative genomic approach to investigate gene content in 63 E. faecalis strains, with a special focus on CC2. Statistical analysis using Fisher's exact test revealed 252 significantly enriched genes among CC2-strains. The majority of these genes were located within the previously defined mobile elements phage03 (n = 51), efaB5 (n = 34) and a vanB associated genomic island (n = 55). Moreover, a CC2-enriched genomic islet (EF3217 to -27), encoding a putative phage related element within the V583 genome, was identified. From the draft genomes of CC2-strains HH22 and TX0104, we also identified a CC2-enriched non-V583 locus associated with the E. faecalis pathogenicity island (PAI). Interestingly, surface related structures (including MSCRAMMs, internalin-like and WxL protein-coding genes) implicated in virulence were significantly overrepresented (9.1%; p = 0.036, Fisher's exact test) among the CC2-enriched genes.In conclusion, we have identified a set of genes with potential roles in adaptation or persistence in the hospital environment, and that might contribute to the ability of CC2 E. faecalis isolates to cause disease.For many years, Enterococcus faecalis was considered as an intestinal commensal, which only sporadically caused opportunistic infections in immunocompromised patients. During the last thirty years, however, E. faecalis has gained notoriety as one of the primary causative agents of nosocomial infections [1,2], including urinary tract infections, endocarditis, intra-abdominal infections and bacteremia. The ability of E. faecalis to cause infection has been connected to inherent enterococcal traits, enabling the bacterium to tolerate diverse and harsh growth conditions. Moreover, several putative enterococcal virulence factors have been characterized (reviewed in [3]), and the role of these virulence factors in pathogenicity have been further established in various animal infection models [4-8] and cultured cell li