Emergence and clonal dissemination of enterococcus faecium and enterococcus faecalis in hospitals, the community and animals

For many years, Enterococcus faecium and Enterococcus faecalis were considered harmless commensals of the digestive tract, which only sporadically caused opportunistic infections in severely ill patients. Over de last two decades, vancomycin resistant enterococci (VRE) have emerged worldwide as an important cause of nosocomial infections, which is mainly due to vancomycin resistant E. faecium (VREF). Molecular epidemiological studies and population genetics of both human- and animal derived E. faecium and E. faecalis isolates using multilocus sequence typing revealed host-specific genogroups for E. faecium, including a hospital associated subpopulation characterized by ampicillin resistance and the presence of the enterococcal surface protein encoding esp gene. In contrast, host-specificity for E. faecalis was not observed although a few high risk complexes were identified, which appeared to be enriched for hospital infection isolates. In this chapter, we focus on the molecular epidemiology and population genetics of enterococci and discuss the most prevalent circulating clonal complexes.