Enterococcus faecium, a major cause of nosocomial infections, is often isolated from conditions where biofilm is considered to be important in the establishment of infections. We investigated biofilm formation among E. faecium isolates from diverse sources and found that the occurrence and amount of biofilm formation was significantly greater in clinical isolates than fecal isolates from community volunteers. We also found that the presence of the empfm (E. faecium pilus) operon was associated with the amount of biofilm formation. Furthermore, we analyzed the possible association between the distribution of 16 putative virulence genes and the occurrence of biofilm production. Even though the prevalence of these virulence genes was significantly higher in clinical isolates, we did not observe any correlation with the occurrence of biofilm formation.
Enterococcus faecium, biofilm, virulence
Enterococci, found naturally as part of the digestive tract flora in humans and animals, have evolved into major opportunistic pathogens causing nosocomial infections including bacteremia in neutropenic patients, endocarditis and device infections (Arias & Murray, 2012). In the USA, there has been a rapid increase in Enterococcus faecium infections associated with hospital outbreaks since the 1980s, often attributed to the emergence of resistance to ampicillin, the increased use of advanced generation cephalosporins and vancomycin and the subsequent development of resistance to vancomycin (Murray, 2000, Somarajan & Murray, 2013). Also, a recent CDC survey reported that about 38% of hospital-associated enterococcal isolates identified to the species level were E. faecium (Hidron, et al., 2008). Over the last two decades, it has been recognized that the vast majority of hospital infection-associated E. faecium, including clonal complex CC17, are part of the hospital-associated clade (Galloway-Pena, et al., 2012, Willems, et al., 2012, Gilmore, et al., 2013); this clade is characterized by, in addition to high-level ampicillin and vancomycin resistance, increased frequency of genes encoding putative virulence determinants such as the enterococcal surface protein (Esp) (Willems, et al., 2001) and MSCRAMMs (microbial surface component recognizing adhesive matrix molecules) (Sillanpaa, et al., 2008, Sillanpaa, et al., 2009), a plasmid encoding a hyaluronidase-like protein (Hylfm, now annotated as family 84 glycosyltransferase) (Rice, et al., 2003), expression of collagen adhesin mediated by acm (Nallapareddy, et al., 2006), and EmpABC (forming the E. faecium pili, previously known as EbpABCfm) (Sillanpaa, et al., 2009).
The clinical impact of E. faecium may be enhanced by biofilm formation and these organisms are frequently found in conditions where biofilm is thought to be important, such as endocarditis, catheter-associated urinary tract infections, periodontitis, and a variety of device-related infections, thereby making it more difficult...