AIM: Staphylococcus aureus is one of the leading causes of nosocomial infections and is known for its ability to develop resistance to antibiotics. The drug susceptibility pattern of Methicillin Sensitive S. aureus (MSSA) and Methicillin Resistant S. aureus (MRSA) may vary. AIMs and Objectives: This study was carried out to determine and compare the drug susceptibility patterns in nosocomial MSSA and MRSA.
MATERIAL AND METHODS: The study was conducted between September 2009 and August 2011. Standard conventional methods were used for the isolation and identification of S. aureus. MRSA was identified by the cefoxitin (30 μg) disk method. Antibiotic susceptibility test was done using Kirby-Bauer disk diffusion method and the interpretation of the results was done using CLSI guidelines.
RESULTS: Out of 685 strains of S. aureus studied, 173(25.25%) were MRSA and 512 (74.25%) were MSSA. Out of 173 MRSA strains, 114(65.89%) were isolated from pus, 22(12.71%) from vaginal swab, 18(10.40%) from central catheter tip and the remaining from other specimens. All isolates were susceptible to vancomycin and least number of isolates were susceptible to penicillin. MRSA displayed significantly higher resistance to other antibiotics. 45.7% of MRSA strains were resistant to clindamycin, 64.7% to ciprofloxacin, 87.3% to cotrimoxazole, 54.3% to erythromycin, 17.3% to gentamicin, 16.8% to netilmycin, and 58.38% to tetracycline. Inducible clindamycin resistance was detected in 37 (21.38%) strains of MRSA.
CONCLUSION: Nosocomial infections caused by MRSA is a significant problem. MRSA and MSSA differ with their susceptibility to antibiotics. All MRSA isolates in our hospitals were susceptible to vancomycin. Proper selection of the antibiotics based on antibiotic susceptibility test results is needed for effective treatment and prevention of emergence of resistance in MRSA and MSSA.