Growing Resistance to Vancomycin among Methicillin Resistant Staphylococcus Aureus Isolates from Different Clinical Samples.

INTRODUCTION: Methicillin resistant Staphylococcus aureus (MRSA), majorly associated with nosocomial and community infections worldwide, are emerging as resistant strains to many antibiotics narrowing down the efficacy of antimicrobial therapy. In order to investigate the changing resistant pattern of MRSA to empirical drugs, the study was carried out at KIST Medical College and Hospital, Nepal. It also aims to determine the minimum inhibitory concentration (MIC) of vancomycin among MRSA.

METHODS: Altogether 3500 clinical samples including 1303 blood, 1489 urine and 708 body fluids were collected and processed. Isolated S. aureus were further screened for methicillin resistance by Kirby-Bauer disk diffusion technique using cefoxitin (30µg) disk. All MRSA were subjected to in vitro determination of MIC of vancomycin by agar dilution method as recommended by CLSI guidelines.

RESULTS: Total 287 S. aureus were isolated from the different clinical samples. Altogether 248 (86.41%) were found to be multidrug resistance (MDR) while 42 (14.63%) of the isolates were methicillin resistance with the highest prevalence in the age group of 16-30. All 42 (100%) MRSA isolates were resistant to ampicillin and penicillin followed by 41 (97.62%), 32 (76.19%), 31(73.81%), 29 (69.05%), 9 (21.43%) and seven (16.67%) to cefotaxime, gentamycin, cotrimoxazole, erythromycin, tetracycline and ciprofloxacin respectively. Although all MRSA strains were sensitive to vancomycin on disc diffusion, four isolates were intermediates in vitro determination of MIC of vancomycin. The break point for vancomycin was found to be 15mm.

CONCLUSIONS: The increment in vancomycin MIC among MRSA is alarming. Strict control measures to prevent MRSA spread and a routine surveillance for VRSA must be incorporated in hospitals.