Characterization and monitoring of linezolid-resistant clinical isolates of Staphylococcus epidermidis in an intensive care unit 4 years after an outbreak of infection by cfr-mediated linezolid-resistant Staphylococcus aureus.

Resistance to linezolid is emerging among Staphylococcus epidermidis isolates. During the 4 years following an outbreak of cfr-mediated linezolid-resistant S. aureus in our intensive care unit in 2008, we analyzed the clinical context and characterized the resistance mechanisms of 100 linezolid-resistant strains of S. epidermidis. The prevalence of the cfr gene in our strains reached 50% alone or in combination with other mechanisms. The mutation G2576T in domain V was found in 22% of strains, and both the cfr gene and G2576T in 44%. We also found an association between the cfr gene and mutations in the ribosomal protein L3. All 3 mechanisms co-occurred in 1 strain. MICs in combinations rose to >256 µg/mL. 58% of colonized patients, and 90% of infected patients had previously received linezolid for at last 10 days. Vancomycin was the main antibiotic in these infections, most of which were bacteremia. We found a high prevalence of the cfr gene in our clinical S. epidermidis isolates after the 2008 outbreak, despite having implemented isolation and control measures. The potential transmissibility of this agent, even without prior exposure to linezolid, can have serious epidemiological repercussions.