Emergence of linezolid resistance in staphylococc isolates

To describe the characteristics of the population from which linezolid-resistant staphylococcus epidermidis (SERL) was isolated, the phenotypic and molecular characteristics of linezolid resistance, to study the clonality of the strains and to quantify the exposure to linezolid during this period. Retrospective observational descriptive study including patients at the CHU de Toulouse in whom linezolid-resistant staphylococcus spp. was identified between 2006 and 2012. Linezolid consumption was provided by the central pharmacy. The mechanism of resistance and clonality of clinical isolates were investigated in the CNR of Lyon (national research centre). SERL was isolated from 29 patients, including 25 patients in intensive care units. Exposure to linezolid was found in 96% of these patients. The emergence of resistant strains coincides with periods of high linezolid prescription. The mutation detected in the 23S rRNA gene is T2504A. This is probably the dissemination of a monoclonal strain of SERL under selection pressure from the high linezolid prescription.