Screening for Mupirocin Resistance in Staphylococcus

INTRODUCTION:Mupirocin is widely used topical antibiotic for the treatment of skin and soft tissue infections caused by Staphylococcus and Streptococcus. In addition nasal formulations are approved for the use in nasal eradication of methicillin-resistant Staphylococcus aureus in patients and health care workers. Wide usage of mupirocin has resulted in resistance leading to treatment failure. AIM:To screen for the mupirocin resistance among the Staphylococcus isolates using disc diffusion and minimum inhibitory concentration method. MATERIALS AND METHODS:A cross-sectional study was done at Microbiology Department of Sri Ramachandra University with 100 strains of Staphylococcus spp isolated from skin and soft tissue infections. Methicillin susceptibility was done by disc diffusion method using oxacillin (1 μgm) and cefoxitin (30 μgm) discs. Isolates were screened for mupirocin resistance by disc diffusion method using 5 μgm discs. High level and low level resistance determined by MIC using agar dilution method. RESULTS:In 100 Staphylococcus spp 56 were Staphylococcus aureus and 44 were CoNS. Among the 56 Staphylococcus aureus 49 (87.5%) were mupirocin susceptible and 7 (12.5%) resistant by 5μg disc diffusion method. However by MIC method 11 (19.6%) were high and low level mupirocin resistant. Out of 44 CoNS 22 (50%) and 18 (41%) were susceptible by disc diffusion and MIC method respectively. Of the 26 resistant CoNS low level and high level mupirocin resistant was observed in 7 (15.9%) and 19 (43.1%) respectively. CONCLUSION:Screening for mupirocin resistance by disc diffusion method is important before attempting decolonisation. Mupirocin resistance is more with CoNS. Disc diffusion method may miss low level Mupirocin resistance.