Emergence of Staphylococcus epidermidis Clinical Isolates with Resistance to Both Mupirocin and Fusidic Acid

Background: In the recent decades, mupirocin and fusidic acid (FA) have become important antimicrobial agents for skin and soft tissue infections (SSTIs) and the eradication of staphylococci colonization. Objectives: The present study aimed at determining the role of mupirocin and FA resistance in controlling Staphylococcus epidermidis infections and eradication of staphylococci colonization. Methods: This study was conducted between January 2012 and December 2015, at a tertiary hospital in Wenzhou, east China, on 711 S. epidermidis clinical isolates collected consecutively from various specimens of inpatients. Polymerase chain reaction (PCR) and DNA sequencing were used to identify mupA conferring high-level mupirocin resistance and fusA mutations. Multi-locus sequence typing (MLST) based on nucleotide sequencing of seven housekeeping genes revealed distinct related clones of methicillin-resistant S. epidermidis (MRSE), as clinically significant isolates. Results: Twelve FA-resistant S. epidermidis clinical isolates were positive for fusB, while only one was positive for fusC. All six S. epidermidis isolates with low-level mupirocin resistance were negative for mupA. However, 23 (35.38%) of 65 isolates with high level of resistance to mupirocin were found to carry this gene. Surprisingly, among 31 isolates with both mupirocin and FA resistance, only two were positive for fusB and only six were positive for mupA. More than 50% of the resistance for 71 mupirocin-resistant isolates and 56 FA-resistant isolates to non beta-lactam included erythromycin, clindamycin, ciprofloxacin, gentamicin and trimethoprim-sulfamethoxazole. Among 31 S. epidermidis isolates with both mupirocin and FA resistance, 15, three, and two belonged to ST2, ST466, and ST23, respectively. ST125 and ST130 were found in one isolate, each. All 15 ST2 S. epidermidis isolates were MRSE with high-level resistance to mupirocin (MICs > 256 mg/L), with similar resistance patterns. Conclusions: Taken together, the present study is the first report of resistance to both mupirocin and FA among S. epidermidis isolates. Dissemination of S. epidermidis ST2 clone with both FA and mupirocin resistance can cause trouble in controlling S. epidermidis infections and eradication of staphylococci colonization.