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, i...
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...on. Even though our study does not find a correlation between the presence of genes and the occurrence of biofilm formation, we recognize the possibility that recent isolates with substantial genomic diversity might yield different results.
In conclusion, our study finds that biofilm formation as measured in a microtiter plate assay occurs at a higher frequency and amount in clinical E. faecium isolates compared to isolates from healthy volunteers, thus suggesting a potential connection between biofilm formation and virulence potential. Our study also suggests that enrichment of emp (pilus) genes may account for the higher amount of biofilm formation associated with clinical isolates, which in turn could enhance their ability to cause infection through increased resistance to antibiotics and innate host defenses (Donelli & Guaglianone, 2004, Fedtke, et al., 2004).
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