Mupirocin is a topical antibiotic that has been used extensively for treating methicillin resistant Staphylococcus aureus (MRSA) associated infections. However, the prevalence of resistance to mupirocin is being increasingly found due to its irrational and widespread use. Retapamulin: a pleuromutilin antibacterial agent is an effective topical antibiotic against these resistant strains. This study was carried out to determine the rates of resistance to mupirocin in MRSA isolates in our patient population, and to estimate the association of such resistance and resistance to other classes of antimicrobial agents in order to consider the effect of the use of mupirocin on the selection of antimicrobial resistant strains. This prospective study was conducted in the Department of Microbiology at VIMS & RC, Bengaluru. 200 Staphylococcus aureus isolates were recovered from various clinical specimens from out patients and in patients admitted into various wards and intensive care units. Isolation and identification of isolates S. aureus isolated from clinical specimens were identified according to the standard laboratory operating procedures. Antimicrobial sensitivity was determined by the Vitek 2 K automated system. All tests and quality assurance procedures were performed and interpreted according to the standards set by the Clinical and Laboratory Standards Institute (CLSI). For fusidic acid and retapamulin The European Committee on Antimicrobial Susceptibility Testing (EUCAST) criteria was used. For the macrolide-lincosamide streptogramin B (MLSB) phenotype (inducible clindamycin resistance encoded by the plasmid-borne gene, erm) was determined by the disc approximation test, clindamycin was reported to be resistant. Mupirocin resistance testing was done by disc diffusion with disc concentration of 5μg and 200μg. Among the 200 Staphylococcus aureus isolates 108 (54%) were MRSA, highest percentage of MRSA strains were from blood isolates (62%), followed by aspirated fluids and pus (59 % and 56 % respectively). Of the 108 MRSA strains, 26 (24%) were mupirocin resistant Staphylococcus aureus (MupRSA). Mupirocin resistance was not detected in methicillin sensitive Staphylococcus aureus (MSSA) isolates. High-level mupirocin resistance was observed in 11% and low-level resistance in 13% of the 108 isolates. Higher prevalence of high level mupirocin resistance was from blood isolates followed by pus (45% and 36.3% respectively), low level mupirocin resistance was maximum seen in the isolates from respiratory secretions (46%). MupRSA was more frequently isolated from ICUs and surgical wards. The mupirocin resistant MRSA strains exhibited resistance to other class of antibiotics also: ampicillin (90%), ciprofloxacin (88%), erythromycin (86%), co trimoxazole (73%). However fusidic acid, vancomycin and linezolid showed sensitivity of 99%, 96% and 96% respectively. All the strains were sensitive to retapamulin. Increase in mupirocin resistance among MRSA isolates is a matter of concern. Antimicrobial stewardship programmes are important to address excessive or inappropriate antimicrobial usage. Alternative agents to mupirocin should be considered to counteract the clinical failure of decolonization regimens and to prevent the selection of multiple resistant strains.

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