Original Research Article
Year: 2018 | Month: September | Volume: 5 | Issue: 9 | Pages: 140-147
Prevalence of Methicillin Resistance & Comparison of Vancomycin Minimum Inhibitory Concentration by E TEST & VITEK 2 in Staphylococcus Aureus Isolates
Himani1, Vinay Kumar Srivastava2
1Assistant Professor, Department of Microbiology, K. D. Medical College Hospital & Research Center, Mathura
2Professor, Department of Psychiatry, K. D. Medical College Hospital & Research Center, Mathura
Corresponding Author: Vinay Kumar Srivastava
ABSTRACT
Introduction: Resistance to methicillin and other β- lactamase resistant penicillins was first observed in Staphylococcus aureus soon after methicillin was introduced into clinical use in Britain in 1961. Methicillin resistant S. aureus (MRSA) is responsible for around 30% or more of all S. aureus infections.MRSA is a multidrug resistant organism that threatens the continued effectiveness of antibiotics worldwide and causes a threat in hospitals and long-term care settings. Vancomycin has been the treatment of choice for serious infections caused by MRSA. But there has been uncertainty regarding the method for detection of minimum inhibitory concentration of vancomycin, clinical relevance of reduced vancomycin susceptibility in S. aureus & increasing concern regarding the efficacy of vancomycin for treatment of MRSA infections.
Materials and Methods: A study was planned to determine the prevalence of methicillin resistance in clinical isolates of S. aureus isolated from samples of patients attending OPDs & IPDs of Career Institute of Medical Sciences, Lucknow. Antimicrobial susceptibility testing was performed by Kirby Bauer disc diffusion method. The isolates were tested for methicillin resistance by using cefoxitin disc (30µg) by disc diffusion method. The results were interpreted according to CLSI criteria. Vancomycin MICs were compared by two methods viz. E TEST & VITEK 2.
Results: A total of 163 isolates were studied and 66(40.4%) were found to be methicillin resistant. MRSA isolates showed greater resistance to multiple drugs as compared to methicillin sensitive S. aureus (MSSA) isolates. 48.48%, 86.36%, and 42.42% of MRSA were resistant to chloramphenicol, cotrimoxazole & doxycycline as compared to 4.12%, 15.46% & 12.37% of MSSA respectively. On determination of MICs for vancomycin for the MRSA isolates, all were identified as VSSA by E Test & Vitek 2 methods but the MIC values were variable on testing with both methods. Out of 66 isolates, 51 isolates had MIC=1.5µg/mL & 15 isolates had MIC = 2 µg/mL by E Test method. When these isolates were tested with Vitek 2, only 20 had MIC=1.5µg/mL while 46 had MIC=2µg/mL.
Conclusion: An ever rising isolation of MRSA from various infections was observed. These isolates were also associated with high level of co-resistance to other group of antibiotics. There is a need to study the epidemiology of such infections. Robust antimicrobial stewardship and strengthened infection control measures are required to prevent spread and reduce emergence of resistance.
Key words: Staphylococcus aureus, Antibiotic susceptibility, MRSA, Vancomycin, MIC
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