Abstract
BackgroundEnterococcus faecalis, traditionally considered a harmless commensal of the intestinal tract, is now ranked among the leading causes of nosocomial infections. In an attempt to gain insight into the genetic make-up of commensal E. faecalis, we have studied genomic variation in a collection of community-derived E. faecalis isolated from the feces of Norwegian infants.ResultsThe E. faecalis isolates were first sequence typed by multilocus sequence typing (MLST) and characterized with respect to antibiotic resistance and properties associated with virulence. A subset of the isolates was compared to the vancomycin resistant strain E. faecalis V583 (V583) by whole genome microarray comparison (comparative genomic hybridization (CGH)). Several of the putative enterococcal virulence factors were found to be highly prevalent among the commensal baby isolates. The genomic variation as observed by CGH was less between isolates displaying the same MLST sequence type than between isolates belonging to different evolutionary lineages.ConclusionThe variations in gene content observed among the investigated commensal E. faecalis is comparable to the genetic variation previously reported among strains of various origins thought to be representative of the major E. faecalis lineages. Previous MLST analysis of E. faecalis have identified so-called high-risk enterococcal clonal complexes (HiRECC), defined as genetically distinct subpopulations, epidemiologically associated with enterococcal infections. The observed correlation between CGH and MLST presented here, may offer a method for the identification of lineage-specific genes, and may therefore add clues on how to distinguish pathogenic from commensal E. faecalis. In this work, information on the core genome of E. faecalis is also substantially extended.
Highlights
Enterococcus faecalis, traditionally considered a harmless commensal of the intestinal tract, is ranked among the leading causes of nosocomial infections
These isolates were considered as legitimate representatives of commensal E. faecalis as they have been resident in the gut without causing any apparent negative effect to the health of the host
A total of 31 community-derived fecal baby isolates were sequence typed by multilocus sequence typing (MLST) and characterized with respect to antibiotic resistance and properties associated with virulence
Summary
Enterococcus faecalis, traditionally considered a harmless commensal of the intestinal tract, is ranked among the leading causes of nosocomial infections. Enterococci are Gram-positive facultative anaerobic cocci with a low GC-content They are natural inhabitants of the mammalian gastrointestinal (GI) tract and among the first lactic acid bacteria to colonize the intestines of a newborn [1]. A large number of reports on enterococcal pathogenicity has focused on the presence or absence of these virulence determinants in enterococcal isolates from different origins [9,10,11,12,13,14]. The results have shown that several of the putative virulence traits are detected in enterococcal isolates independent of their origin, suggesting that these factors may not be crucial for enterococcal pathogenicity. A higher incidence of some of the virulence determinants in clinical isolates may indicate that these genes enhance the ability of E. faecalis to cause disease, as suggested by virulence studies on bacterial mutants in animal models [3]
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