J Antimicrob Chemother. 2021 Apr 1:dkab098. doi: 10.1093/jac/dkab098. Online ahead of print.
BACKGROUND: Current antimicrobial susceptibility/resistance data versus skin and soft tissue infection (SSTI) pathogens help to guide empirical treatment using topical antimicrobials.
OBJECTIVES: To assess the in vitro activity and resistance rates of fusidic acid, mupirocin, ozenoxacin and comparator agents against pathogens isolated from patients with SSTIs in Canada.
METHODS: SSTI isolates of MSSA (n = 422), MRSA (n = 283) and Streptococcus pyogenes (n = 46) obtained from CANWARD 2007-18 were tested using CLSI broth microdilution. Fusidic acid low-level resistance was defined as an MIC of ≥2 mg/L and high-level resistance as an MIC ≥512 mg/L. Mupirocin high-level resistance was defined as an MIC ≥512 mg/L and low-level resistance was an MIC of 2-256 mg/L.
RESULTS: Low-level and high-level fusidic acid resistance in MSSA was 10.9% and 1.7%, respectively. Low-level and high-level fusidic acid resistance in MRSA was 10.6% and 3.5%, respectively. High-level mupirocin resistance was identified in 1.4% of MSSA and 14.1% of MRSA, respectively. Versus MSSA, ozenoxacin demonstrated MIC50 and MIC90 of 0.004 and 0.25 mg/L, respectively. Against MRSA, ozenoxacin inhibited all isolates at an MIC of ≤0.5 mg/L, including isolates with ciprofloxacin MICs >2 mg/L, clarithromycin-resistant, clindamycin-resistant, high-level fusidic acid-resistant and high-level mupirocin-resistant isolates.
CONCLUSIONS: We conclude that fusidic acid low-level resistance exceeded 10% for both MSSA and MRSA while fusidic acid high-level resistance was ≤3.5%. Mupirocin high-level resistance exceeded 10% in MRSA. Ozenoxacin is active versus SSTI pathogens including MRSA resistant to fluoroquinolones, macrolides, clindamycin, fusidic acid and mupirocin.