International Journal of Health and Rehabilitation Sciences

Abstract
Background: The antimicrobial chemotherapy for Staphylococcus aureus infections has been empirical as this species has overcome most of the therapeutic agents. S. aureus is among most common organisms in hospital and community acquired infections. In recent years, a large and continuing increase in the prevalence of methicillin resistant S. aureus (MRSA) has been observed. In addition, the emergence of S. aureus with reduced susceptibility or resistance to vancomycin also has been reported

Objective: To evaluate vancomycin susceptibility in clinical isolates of Methicillin resistant Staphylococcus aureus (MRSA) for a period of three years (2009-2011) in a tertiary care hospital.

Materials and Methods: A total of 400 clinical isolates of S. aureus from in-patients (pus, sputum, blood and body fluids) at Yenepoya University Hospital from July 2009 to June 2011 were included in the study. The specimens from the patients were cultured on blood agar. The isolates were identified by Gram’s stain, catalase test, mannitol fermentation test, free coagulase and deoxyribonuclease test according to standard techniques. Antibiogram and minimum inhibitory concentration (MIC) of all the MRSA isolates for vancomycin were determined by Kirby Bauer’s disc diffusion method and macro broth dilution procedure respectively, according to the 2009 CLSI guidelines. Results were interpreted as susceptible if the MIC was ≤ 2µg/ml, 4-8µg/ml as intermediate and ≥16 µg/ml as resistant.

Results: A total of 400 strains of S. aureus collected over three year period were included in the study. Of these, 104 (26%) were MRSA. All the MRSA isolates were susceptible to vancomycin by disc diffusion method as well as MIC. 30 (28.8%) were with MIC of 0.5 µg/ml, 67 (64.4%) were with 1µg/ml and 07 (6.7%) with 2µg/ml. There was an increase in the percentage of isolates from 0.5µg/ml to 1µg/ml during the study period of three years.

Conclusion: There is an increase in the number of strains with MICs of 1µg/ml. This may indicate a step towards development of VISA and possibly VRSA. Continuous monitoring of MIC levels of vancomycin in MRSA is warranted.