Intensive care unit dissemination of multiple clones of linezolid-resistant Enterococcus faecalis and Enterococcus faecium.

OBJECTIVES Outbreaks caused by linezolid-resistant (LR) enterococci remain rare. We report the epidemiological and molecular characteristics of the multiclonal dissemination of LR enterococci in the intensive care unit (ICU) of a Greek hospital. METHODS All LR enterococcal isolates recovered from patients hospitalized in the ICU of the University Hospital of Larissa, Greece, between January 2007 and October 2008 were included. Isolates were tested by PFGE and PCR followed by sequence analysis of the entire 23S rRNA gene. Patient records were retrieved to access patterns of acquisition and outcome. RESULTS Sixteen separate patients were infected and/or colonized by 22 LR enterococcal isolates (17 Enterococcus faecium and 5 Enterococcus faecalis). Linezolid MICs varied from 8 to 16 mg/L; 12 isolates showed cross-resistance to vancomycin. Genotyping revealed as many as seven and three PFGE types among E. faecium and E. faecalis isolates, respectively, indicating multiclonal spread of LR enterococci. Nine patients had received linezolid prior to the recovery of LR enterococci, while the remaining seven patients were not exposed to the drug. All isolates carried the mutation G2576T; the mutated position was heterogeneous in 12 isolates and homogeneous in 10. CONCLUSIONS The multiclonal composition of LR enterococci indicates that linezolid resistance possibly occurred on several independent occasions. Its acquisition was often not related to linezolid administration; patients might have acquired their LR isolate from another patient that had received linezolid or, alternatively, resistance may have arisen by mutation that occurred independently.