A PROSPECTIVE STUDY ON METHICILLIN RESISTANCE AND INDUCIBLE CLINDAMYCIN RESISTANCE IN STAPHYLOCOCCUS AUREUS ISOLATES IN A TERTIARY CARE HOSPITAL

MRSA

Abstract

Methicillin-resistant S. aureus (MRSA) poses an even greater challenge, as its resistance to multiple antibiotics makes infections increasingly difficult to treat. The difficulty in treating MRSA infections has led to a resurgence of interest in alternative antibiotic classes, particularly Macrolide-Lincosamide- Streptogramin B (MLSB) antibiotics. Hence the present study aims to identify the inducible clindamycin resistance in S. aureus strains and to ascertain the relationship between methicillin-resistant S. aureus (MRSA) and inducible clindamycin resistance and effectiveness of commonly used antibiotics in such strains. A prospective study was conducted for a period of one year in the department of microbiology, tertiary care teaching hospital after obtaining a Institutional ethics clearance. All the samples from both Out-patients and In-patients received from various clinical departments were processed using standard microbiological procedures. A total of 173 samples showed the growth of Staphylococcus aureus. MRSA isolates were identified phenotypically using the cefoxitin disc diffusion method, while inducible clindamycin resistance was assessed using the D-zone test. Chi-square test, Logistic regression analysis will be conducted to identify significant predictors. A decision tree algorithm was applied to explore classification patterns. Among 173 samples screened for the presence of MRSA/MSSA, 24.27% of samples showed the growth of MRSA and 75.72% of samples showed the growth of MSSA. Majority of MRSA strains showed resistance to penicillin antibiotic 95.2% followed by ciprofloxacin 88.09%. Most of the MRSA were sensitive to linezolid 92.8%, cotrimoxazole 88.09% and tetracycline 83.3%. Ten MRSA strains that are known to be positive for constitutive MLSB (cMLSB phenotype) resistance and these strains carry erm genes (most commonly ermA, ermC, or ermB) that confer macrolide-lincosamide-streptogramin B (MLSB) resistance. 3 isolates were resistant to erythromycin, susceptible to clindamycin, and positive for the D-test, indicating the inducible MLSB (iMLSB) phenotype. The findings should be interpreted considering the absence of molecular confirmation and limited resistant isolate numbers. The rate of inducible clindamycin resistance (iMLSB) detected by the D-test in our isolates was only 6.9%, which is relatively low compared to many reports. This suggests that clindamycin may remain a viable therapeutic option in our setting. However, continued surveillance and routine D-testing are essential to monitor emerging resistance and guide appropriate antibiotic use.