MINIMUM INHIBITORY CONCENTRATION OF LINEZOLID IN CLINICAL ISOLATES OF METHICILLIN-RESISTANT STAPHYLOCOCCUS AUREUS AT A TERTIARY CARE HOSPITAL

Background: Methicillin-resistant Staphylococcus aureus (MRSA) is a major cause of hospital and community-acquired infections, with substantial impact on infection rates, morbidity, mortality, and healthcare costs. Vancomycin, remained a longstanding cornerstone in MRSA treatment, butthe emergence of vancomycin resistant MRSA (VRSA), necessitates alternative antimicrobial solutions. Linezolid, stands out as a promising candidate. Linezolid antibiotic is available as an oral formulation for resistant staphylococcal infections. It has unique advantages such as an absence of renal toxicity and improved lung parenchymal diffusion compared. However, emerging resistance to linezolid has become a concern worldwide. There is clonal dissemination of Linezolid Resistant Staphylococcus aureus (LRSA) within or across healthcare settings which demands continuous surveillance to determine the emergent risk of resistant strains and to establish guidelines for appropriate use. Objectives: To determine the minimum inhibitory concentration (MIC) of linezolid among MRSA isolates and to compare Kirby-Bauer disk diffusion method with MIC testing by agar dilution method for linezolid resistance detection. Methods: A hospital-based descriptive study was conducted over one year in the Department of Microbiology, Guru Gobind Singh Medical College & Hospital, Faridkot. Two hundred clinically significant MRSA isolates obtained from various clinical specimens were included. Identification and antimicrobial susceptibility testing were performed according to CLSI guidelines. Linezolid susceptibility was assessed using Kirby–Bauer disk diffusion and agar dilution MIC methods. Results: Of the 200 MRSA isolates, maximum MRSA were isolated from pus (67.5%) followed by blood (30.5%). All MRSA isolates were susceptible to linezolid by both disk diffusion and MIC methods. MIC distribution showed that 85.5% isolates had MIC ≤0.25 µg/mL, 8% had MIC 0.5 µg/mL, 3.5% had MIC 1 µg/mL, and 3% had MIC 2 µg/mL. No isolate demonstrated resistance (MIC≥8 µg/mL). MIC50, MIC90, and geometric mean MIC were 0.25 µg/mL, 0.5 µg/mL, and 0.2952 µg/mL respectively. Perfect agreement was observed between disk diffusion and agar dilution method (Kappa = 1). Conclusion: Linezolid demonstrated excellent in vitro activity against MRSA isolates in the present study. Routine surveillance of MIC trends remains essential for early detection of emerging resistance and prevention of linezolid MIC creep.