In vitro vancomycin susceptibility amongst methicillin resistant Staphylococcus aureus.
BACKGROUND
Vancomycin is drug of choice for treatment of Methicillin Resistant Staphylococcus aureus (MRSA) infections. S. aureus with reduced vancomycin susceptibility (SA-RVS) is on rise. Current guidelines of detection of SA-RVS are based on MIC (Minimum Inhibitory Concentration) by broth or agar dilution methods. Vancomycin MIC by E test (Epsilometer Test) is an alternative. A study was undertaken to know the prevalence of SA-RVS and compare vancomycin MIC by agar dilution and E test.


METHODS
A prospective study was undertaken at tertiary care hospital; 232 clinical MRSA isolates were included. Vancomycin MIC was undertaken by agar dilution method and E test.


RESULTS
All isolates were sensitive to Linezolid. Two MRSA isolates had vancomycin MIC ≥4 μg/ml; vancomycin MIC50 and MIC90 of MRSA isolates was 0.5 and 0.2 μg/ml respectively by agar dilution method. There was agreement over 93.5% isolates in vancomycin susceptibility by agar dilution and E test. E test had sensitivity and positive predictive value of 1.0 (CI - 0.34-1.0) and 0.5 (CI - 0.17-0.83) respectively compare to agar dilution method.


CONCLUSIONS
MRSA isolates continues to be susceptible to vancomycin and Linezolid. E test was found equally suitable in initial screening for vancomycin susceptibility. Due to geographic variation in prevalence, there is need of ongoing surveillance of SA-RVC.
Associate Professor, Department of Microbiology, Armed Forces Medical College, Pune 411040, India.
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Chaudhari
Medical Officer (Microbiology), Military Hospital Gwalior, India.
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Tandel
Associate Professor, Department of Microbiology, Armed Forces Medical College, Pune 411040, India.
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Grover
Resident, Department of Microbiology, Armed Forces Medical College, Pune 411040, India.
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Bhatt
Professor & Head, Department of Microbiology, Armed Forces Medical College, Pune 411040, India.
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Sahni
Senior Advisor (Pathology, Microbiology & Virology), Army Hospital (R&R), Delhi Cantt 10, India.
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Sen
Professor & Head (Microbiology), AIIMS, Bhubaneswar, Orissa, India.
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Prahraj
Agar dilution method; E-test (Epsilometer Test); MRSA; Staphylococcus aureus; Vancomycin