Long-term endemic situation caused by a linezolid- and methicillin-resistant clone of Staphylococcus epidermidis in a tertiary hospital

Abstract Background Linezolid (LZD) resistant Staphylococcus epidermidis (LRSE) are increasing mainly associated with outbreaks in hospital wards with high LZD consumption. Aims To investigate the frequency of LRSE in a tertiary hospital, in the context of LZD use. Methods The frequency of LRSE and the data on LZD usage (expressed as DDDs per 100 patient-days), from 2011 to 2017, were retrospectively analysed. Selected LRSE were typed by PFGE and screened for transferable LZD resistance genes. Representative isolates were typed by MLST and ribosomal mechanisms of LZD resistance investigated. Findings A total of 435 LRSE were detected, with frequencies ranging from 13.56 to 32.93% in the ICU, where LZD consumption was high (6.34 to 8.10 DDDs), and from 2.48 to 6.80% in the remaining wards, where LZD use was considerably lower (0.63 to 2.49 DDDs). The first 44 LRSE isolates recovered (June 2013-June 2014) proved to be closely-related according to PFGE patterns, and all except one were resistant to methicillin due to mecA production. Selected isolates belonged to ST2, carried SSCmec III, and had the G2576T mutation in the V domain of each of the six copies of the 23S rRNA gene. Five out of the 44 isolates (11.36%) were positive for the cfr gene. Conclusion An ST2 LZD- and methicillin-resistant clone was established in the whole hospital, not only in the ICU but also in wards where LZD consumption is low. This highlights the need to implement and maintain infection control measures as well as antimicrobial stewardship programs in all hospital units, to preserve the efficacy of LZD.