Prevalence of mupirocin resistance among invasive coagulase-negative staphylococci and methicillin-resistant Staphylococcus aureus (MRSA) in France: emergence of a mupirocin-resistant MRSA clone harbouring mupA.

Mupirocin is the cornerstone of decolonization regimens, a successful strategy to prevent healthcare-associated staphylococcal infections. Several recent studies have reported alarming results: (i) an extending reservoir of mupA, the ancestral mobile resistance gene, among coagulase-negative staphylococci (CoNS); (ii) the emergence of a new resistance gene (mupB); and (iii) a growing number of mupirocin-resistant methicillin-resistant Staphylococcus aureus (MRSA), including highly pathogenic clones. We performed a nationwide prospective study in France to detect such trends among invasive staphylococci. Between October 2011 and February 2012, 367 MRSA and 708 CoNS invasive isolates were collected from 37 hospitals and analysed centrally. Mupirocin MICs were determined using the broth microdilution method. mupA/B PCR was performed for resistant isolates (MIC 1 mg/L). Genetic relatedness between mupirocin-resistant MRSA isolates was determined by PFGE analysis and related isolates were tested by microarray. Among MRSA isolates 2.2 (n8) were classified as mupirocin resistant; 1.4 (n5) showing low-level resistance (MIC 256 mg/L) and 0.8 (n3) high-level resistance (MIC 256 mg/L). Only the latter isolates carried mupA. A clonal relationship was identified between two mupA-negative MRSA from the same hospital and three mupA-positive MRSA from three distant towns; these three isolates belonged to the Lyon clone. Mupirocin resistance was identified in 10.3 of CoNS, mainly highly resistant mupA-positive isolates (5.6). The mupB gene was not detected in mupirocin-resistant MRSA or CoNS. This first large national study indicates the need for thorough epidemiological monitoring and a stewardship programme to prevent and detect mupirocin resistance in staphylococci.