Mupirocin resistance in clinical isolates of methicillin-resistant Staphylococcus aureus from a tertiary care rural hospital

Abstract

Background and Aims: Mupirocin is a topical antibiotic that has been used extensively for treating methicillin-resistant Staphylococcus aureus (MRSA) associated infections. However, the prevalence of mupirocin-resistant MRSA has increased with the extensive and widespread use of this agent. The aim was to determine the rates of high-level and low-level mupirocin resistance in MRSA to study the antimicrobial resistance pattern and clindamycin resistance in mupirocin-resistant MRSA. Methods: A total of 267 non-duplicate clinical isolates of MRSA from various clinical specimens were tested for mupirocin resistance by the disk diffusion method using 5 and 200 μg mupirocin disks. MRSA isolates were tested for antibiotics by Kirby-Bauer disk diffusion method as per Clinical and Laboratory Standards Institute (CLSI) guidelines. Erythromycin-resistant isolates of MRSA were further studied for inducible clindamycin resistance by D test as per CLSI guidelines. Results: Of 267 MRSA isolates, high-level mupirocin resistance was observed in 5.99% and low-level resistance in 15.35%. Mupirocin-resistant MRSA isolates showed higher antibiotic resistance to fusidic acid (14.03% vs 7.14%), rifampicin (5.26% vs 2.38%), erythromycin (68.42% vs 58.57%), and clindamycin (52.63% vs 45.71%). No MRSA strains were found to be resistant to vancomycin and linezolid. Mupirocin-resistant MRSA isolates showed higher constitutive macrolide-lincosamide-streptogamin B (cMLS B ; 51.28% vs 42.98%) and inducible macrolide-lincosamide-streptogamin B (iMLS B ; 17.94% vs 13.15%) resistance, as compared to mupirocin-sensitive MRSA isolates. Conclusion: The emergence of mupirocin resistance could be limited by regular surveillance and effective infection control initiatives so to inform health care facilities to guide therapeutic and prophylactic use of mupirocin.