Linezolid resistance in Staphylocccus epidermidis: Another armour in the armamentarium of the so called commensal

Whereas previously only regarded as an innocuous commensal microorganism on the human skin, Staphylococcus epidermidis is nowadays seen as an important opportunistic pathogen. In particular, S. epidermidis represents the most common source of infections on indwelling medical devices such as peripheral or central intravenous catheters. Linezolid, the first approved oxazolidinone antibiotic, is a useful therapeutic option in the management of infections caused by multidrug-resistant Gram-positive bacteria. The previous administration of linezolid has been reported to be an independent predictor of linezolid resistance in coagulase-negative staphylococci (CoNS). Cases of patients developing infections with linezolid-resistant CoNS in the absence of prior exposure to linezolid have also been reported. The source of the resistant strain remains undetermined, but the clonal spread of CoNS has been reported to occur within hospitals, and therefore, the possibility of nosocomial transmission from patients colonized with linezolid-resistant CoNS following linezolid exposure needs to be entertained. Besides linezolid resistance, linezolid dependence has also been documented. All harboring linezolid-dependent linezolid-resistant S. epidermidis (LRSE) had prolonged linezolid treatment before yielding LRSE. This exposure also may have fostered the transition from resistance to dependence as suggested previously in vancomycin-dependent enterococci. Therefore, the high intrahospital linezolid consumption may favor not only LRSE selection but also their competitive survival. Should linezolid dependence prove common in highly LRSE isolates, it could explain their increasing clinical occurrence and the emergence of LRSE outbreaks. Our reports describe the first few cases of clinical failure of linezolid treatment due to LRSE in India.