Current status of vancomycin susceptibility against methicillin resistant Staphylococcus aureus (MRSA) strains: A study at two tertiary care hospitals of Pakistan

Vancomycin has been considered mainstay treatment of infections caused by methicillin-resistant Staphylococcus aureus. The reports of the emergence of vancomycin intermediate and vancomycin resistant S. aureus from various parts of the world have been of great clinical concern. This study was performed to monitor the status of glycopeptide susceptibility against methicillin resistant S. aureus in our set up. All non-duplicate methicillin resistant Staphylococcus aureus (MRSA) isolates recovered during the period of study from various wards of Military Hospital Rawalpindi and PAEC General Hospital Islamabad, were subjected to the detection of minimum inhibitory concentrations of vancomycin using E-strips. Results were analyzed to evaluate the possible presence of vancomycin intermediate and resistant strains in the set up. A total of 276 methicillin-resistant S. aureus isolates were studied. The range of vancomycin minimum inhibitory concentrations (MIC) was 0.19 to 3 μg/mL. MIC 50 came out to be 0.75 μg/mL whereas the MIC 90 was 1.5 μg/ mL. 128 out of 276 (46%) isolates had vancomycin MIC equal to or greater than 1 μg/mL. Majority of the isolates (69%) were from pus samples. No vancomycin resistant or intermediate strain of MRSA was isolated during the study but there were a significant number of isolates having ≥ 1 µg/ml MIC of vancomycin.   Key words: E- test, methicillin resistant Staphylococcus aureus, minimum inhibitory concentrations (MIC), susceptibility, vancomycin.