PHENOTYPIC CHARACTERISATION OF MACROLIDE-LINCOSAMIDE-STREPTOGRAMIN B (MLSB) RESISTANCE IN STAPHYLOCOCCUS AUREUS ISOLATED FROM CLINICAL SAMPLES AT A TERTIARY CARE HOSPITAL IN CENTRAL INDIA
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Keywords
Staphylococcus aureus, MRSA, clindamycin resistance, D-test, iMLSB, cMLSB, VITEK-2.
Abstract
Background: Staphylococcus aureus remains a major cause of both hospital-acquired and community-acquired infections. Resistance to macrolide-lincosamide-streptogramin B (MLSB) antibiotics compromises clindamycin therapy, an important alternative for treating methicillin-resistant S. aureus (MRSA). Accurate phenotypic detection of inducible resistance prevents treatment failures and contributes to antimicrobial stewardship.
Objectives: To identify constitutive (cMLSB), inducible (iMLSB), and MS phenotypes among S. aureus isolates using the D-test and compare the results with automated VITEK-2 system outcomes.
Methods: This cross-sectional study included 250 S. aureus isolates collected from patients attending various departments of Index Medical College Hospital & Research Centre (IMCHRC), Indore, between November 2021 and May 2024. Isolates were identified using standard microbiological procedures, and antimicrobial susceptibility testing was performed according to CLSI guidelines. The D-test was conducted for all erythromycin-resistant isolates, and the results were correlated with VITEK-2 findings. Statistical analysis was performed using SPSS v25.
Results: Among the 250 isolates, 148 (59%) were MRSA and 102 (41%) were MSSA. D-test identified 26% of MRSA and 11% of MSSA as iMLSB, and 40% of MRSA and 11% of MSSA as cMLSB. The D-test showed 57.7% sensitivity and 100% specificity compared with VITEK-2. A statistically significant association (p < 0.05) was observed between MRSA and inducible resistance.
Conclusion: Routine implementation of the D-test is essential in diagnostic microbiology to identify inducible clindamycin resistance, especially in MRSA isolates. Early detection prevents therapeutic failure and helps formulate targeted antibiotic policies.
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Ms Tripti Mani Tripathi
PhD Scholar, Department of Microbiology, Index Medical College Hospital & Research Centre, Indore, India. (Malwanchal University)
Dr Ramanath Karicheri
Professor, Department of Microbiology, Index Medical College Hospital & Research Centre, Indore, India. (Malwanchal University)