Insight into antimicrobial susceptibility and population structure of contemporary human Enterococcus faecalis...

To investigate antimicrobial susceptibility and clonal relatedness of Enterococcus faecalis human isolates recovered recently (2006-09) in six European countries.

Antimicrobial susceptibility of 386 isolates from Denmark, Germany, Norway, Poland, Spain and The Netherlands, from hospital infections (223 isolates), carriage (82 isolates) and from colonization in the community (81 isolates) was determined by the broth microdilution method. Clonal relatedness of isolates was assessed by multilocus sequence typing.

All isolates were susceptible to benzylpenicillin, ampicillin, linezolid, tigecycline and daptomycin. Non-susceptibility to tetracycline (77.6%), rifampicin (57.3%), ciprofloxacin (51.2%), aminoglycosides (43.3% high-level gentamicin resistance, 40.0% high-level streptomycin resistance) was frequent among hospital isolates, while non-susceptibility to glycopeptides was rare and associated mostly with vanA. Multidrug resistance was found in 59.7% of hospital isolates and 16.1% of community isolates. Isolates were classified into 105 sequence types (STs), of which 21 STs, representing more than half of the collected isolates (53.9%), grouped with 6 large E. faecalis clonal complexes (CCs; CC2, CC16, CC21, CC30, CC40 and CC87). Two of these, CC2 (frequently recovered in Spain and The Netherlands) and CC87 (prevalent in Poland), were found almost exclusively in hospitals and included the highest proportion of multiresistant isolates.

While hospital-acquired E. faecalis in Europe remains susceptible to ampicillin and glycopeptides, the high prevalence of strains that are highly resistant to aminoglycosides excludes these antibiotics from combination therapies. Genotyping revealed that nosocomial infections by multiresistant E. faecalis are largely caused by only a few hospital-associated clones.