Burden of mupirocin resistance among methicillin-resistant Staphylococcus aureus- Colonised patients at a tertiary care medical centre

Objectives: To study the prevalence of mupirocin resistance among methicillin-resistant Staphylococcus aureus (MRSA) colonised patients. Material and Methods: A total of 58 patients in whom MRSA was isolated from clinical samples were screened for MRSA colonisation. For the detection of MRSA colonisation, swabs from three sites (nasal, axillary, and groin) were collected and inoculated on nutrient agar and CHROMagar MRSA. The culture plates were incubated at 37°C for 24 hours. Growth obtained on nutrient agar was then subjected to various biochemical tests and the cefoxitin disc diffusion test according to Clinical and Laboratory Standards Institute 2024 guidelines to detect MRSA colonisers, while the appearance of a green-coloured colony on CHROMagar also established the MRSA colonisation. MRSA isolates from the established coloniser patients were then subjected to mupirocin susceptibility testing using the E-test strip. Results: Out of 58 patients that were screened,18/58 (31.0%) patients showed colonisation by MRSA. Among them, 4/58(6.9%) showed axillary colonisation, 12/58 (20.7%) showed nasal colonisation, 2/58(3.4%) showed groin colonisation, 4/58 (6.9%) showed overlapping carriage in 2 sites (nasal and axilla), and 40/58 (40%) showed no colonisation of MRSA. Out of 18 MRSA isolates that were subjected to mupirocin susceptibility, 2/18(8.6%) showed high-level mupirocin resistance (minimum inhibitory concentration (MIC) ≥ 512 µg/ml), 1/18(5.2 %) showed low-level mupirocin resistance (MIC 8 to 256 µg/ml), and 15/18 (86.2%) were mupirocin sensitive (MIC ≤ 4 µg/ml). Conclusion: Mupirocin resistance among MRSA colonisers is an emerging concern, particularly in healthcare settings. Thus, surveillance of the same is important to retain the usefulness of this drug for the treatment of Staphylococcal infections.