IP International Journal of Medical Microbiology and Tropical Diseases


A study on determination of Minimum Inhibitory Concentration (MIC) of Vancomycin of MRSA Isolates and their impact in treatment of MRSA Isolates


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Author Details: Mathavi Suresh Kumar, Vijai Radhika, Kavitha A, Sasikala G, Indra Priyadharsini

Volume : 3

Issue : 1

Online ISSN : 2581-4761

Print ISSN : 2581-4753

Article First Page : 16

Article End Page : 19


Abstract

Introduction: Staphylococcus aureus is one of the most common causes of nosocomial infections. Methicillin-resistant S. aureus (MRSA) is among the top three clinically important pathogens. The glycopeptide vancomycin is considered to be the best alternative for the treatment of MRSA. MRSA usually exhibit vancomycin-susceptible phenotype (VSSA) but some strains exhibit reduced susceptibility to vancomycin which can be heterogeneous-intermediate (hVISA), intermediate (VISA) or fully resistant (VRSA) phenotypes which results in treatment failure. More recently, poor clinical outcome is observed in infections with MRSA strains with an elevated levels of vancomycin MIC within the susceptible range.
Aim: This study was done to know the prevalence of MRSA and to determine the vancomycin MIC.
Materials & Methods: S.aureus isolated from clinical samples were screened for methicillin resistance using cefoxitin discs (30 μg). The vancomycin MIC of these MRSA isolates was determined using E-strips.  
Results & Discussion: A total of 102 isolates of S.aureus were subjected to study. Among these, 42 isolates were MRSA (41.2%). The different MIC values are as follows: 0.38 μg/mL (2 isolate), 0.75 μg/mL (1 isolate), 1 μg/mL (3 isolates), 1.5 μg/mL (32 isolates) & 2 μg/mL (4 isolates). Although all the MRSA strains were within the susceptible range of vancomycin MIC, their increased MIC values (>1 μg/mL) can lead to treatment failures.
Conclusion: Increased risks of treatment failure has been observed in infections caused by MRSA isolates with vancomycin MIC in the upper end of susceptible range (MIC > 1µg/ml), emphasising the need for determination of vancomycin MIC to assess the treatment outcome.

Keywords:
S.aureus, Methicillin, Vancomycin, Minimum Inhibitory Concentration (MIC), treatment failure