Comparative evaluation of MIC of Vancomycin among methicillin resistant Staphylococcus aureus (MRSA) isolates in tertiary care hospital

Abstract

Vancomycin, a glycopeptide antibiotic with in-vitro activity against all staphylococci and clinical response to methicillinresistant staphylococcus aureus (MRSA) infection, became the backbone of treatment due to MRSA’s universalresistance to the antimicrobial agents belonging to beta-lactams and There are no other viable options. In patients withstaphylococcal infections, this study demonstrated a significant conflict of minimum inhibitory concentrations (MICs) ofvancomycin for MRSA strains between an automated system, Vitek 2, and the method. test E-strip. In the Microbiologylaboratory of JSS hospital which is a tertiary care center situated in Mysuru, 90 isolates were acquired from variousclinical samples to analyse Vancomycin MIC. Out of 90 isolates, 2.2% MRSA isolates showed highest vancomycin MIC2μg/ml by Vitek-2 method, where no isolates showed MIC up-to 2μg/ml by E-strip method. But the higher vancomycinMIC 1μg/ml was observed in 82.2% by vancomycin E-strip method compared to 37.7% by Vitek-2 method. Lowest MIC0.5μg/ml showed by Vitek-2 method in 58.8% compared to 4.4% by E-strip method. The study concludes that all S. aureusisolates were resistant to methicillin by both Vitek-2 system and cefoxitin disc diffusion method and also identified asVSSA (vancomycin susceptible Staphylococcus aureus) by Vitek-2 and E-test method. Higher vancomycin MIC ≥1μg/mlin 93.3% may be due to using of vancomycin improperly and infrequently in MRSA infection with lowest MIC value.Therefore, this method can also be used as routine laboratory practice or as alternative method where Vitek 2 system orother methods are not available.