ASSOCIATION OF DIFFERENT PHENOTYPES OF MLSB AND MUPIROCIN RESISTANCE IN CLINICAL ISOLATES OF STAPHYLOCOCCUS AUREUS

Abstract

Introduction: Staphylococcus aureus is a major human pathogen responsible for a wide range of infections, with methicillin-resistant Staphylococcus aureus (MRSA) posing significant treatment challenges due to its resistance to multiple antibiotics. This study aimed to investigate the association of different phenotypes of macrolide-lincosamide-streptogramin B (MLSB) resistance and mupirocin resistance in clinical isolates of S. aureus, focusing on the prevalence and distribution of resistance patterns in MRSA and methicillin-sensitive S. aureus (MSSA).

Methodology: This cross-sectional study was conducted at a Tertiary Care Hospital. A total of 223 clinical isolates of S. aureus were collected, including 58 MSSA and 165 MRSA isolates. Antimicrobial susceptibility testing for erythromycin, clindamycin, and mupirocin was performed using the Kirby-Bauer disk diffusion method. MLSB resistance phenotypes were determined using the D-test. Statistical analysis was conducted to compare the prevalence of resistance between MRSA and MSSA isolates, with odds ratios (OR) and 95% confidence intervals (CI) calculated, and p-values determined using chi-square tests.

Results: The overall prevalence of MLSB resistance was 55.6%, with MRSA isolates showing a higher prevalence (61.2%) than MSSA isolates (39.7%). The OR for MLSB resistance in MRSA compared to MSSA was 0.416 (95% CI: 0.228 to 0.758, p=0.003). Among erythromycin-resistant S. aureus isolates, the constitutive MLSB (cMLSB) phenotype was most prevalent, particularly in MRSA (53 isolates) compared to MSSA (12 isolates). Mupirocin resistance in MRSA isolates was observed in 10 isolates with high-level resistance (HLR) and 14 with low-level resistance (LLR), with the iMLSB phenotype showing the highest number of resistant isolates.

Conclusion: The study highlights a higher prevalence of MLSB and mupirocin resistance in MRSA isolates compared to MSSA, indicating the need for comprehensive resistance testing and judicious use of antibiotics. These findings underscore the importance of detecting inducible MLSB resistance and monitoring mupirocin resistance to effectively manage S. aureus infections.