CHANGING TRENDS IN SUSCEPTIBILITY PATTERN OF METHICILLIN RESISTANT STAPHYLOCOCCUS AUREUS TO ROUTINELY USED ANTIBIOTICS: A POSSIBLE THREAT -

Objective: To assess the in vitro antimicrobial susceptibility pattern of the Methicillin resistant Staphylococcus aureus (MRSA) isolated from routine clinical specimens. Study Design: Cross-sectional study. Place and Duration of Study: The study was conducted over a period of 2 years (June 2011 – June 2013) in the Department of Microbiology, Army Medical College, National University of Science and Technology, Islamabad, Pakistan. Material and Methods: A total of 149 MRSA isolates were obtained using standard microbiological techniques from various clinical specimens. In vitro susceptibility testing against routinely used antimicrobials was performed by Modified Kirby-Baeur disc diffusion technique as per Clinical and Laboratory Standards Institute (CLSI) guidelines 2013. The isolates were tested for methicillin resistance by using oxacillin disc by disc diffusion method and confirmed by agar screen test (oxacillin 6 µgm/ml). Results: We obtained 114, 25 and 10 isolates from pus, blood and tips respectively. MRSA was found to be highly susceptible to vancomycin 149 (100%), linezolid 144 (96.7%), minocycline 143 (96.3%) and showed moderate susceptibility to rifampicin 111 (74.7%), fusidic acid 99 (66.7%) and chloramphenicol 93 (62.6%). Low in vitro susceptibility was associated with clindamycin 82 (54.7%), tetracycline 79 (53.0%), ciprofloxacin 44 (29.4%), cotrimoxazole 33 (23.6%), gentamicin 34 (22.5%) and erythromycin 26 (17.6%). The susceptibility rates of linezolid and chloramphenicol for MRSA were found to be declining over a period of 2-3 years when compared with previous available data. The data was analyzed using Statistical Package for Social Sciences (SPSS) 19. Frequency of susceptibility for each antimicrobial agent was determined by calculating the percentages. Conclusion: MRSA is rapidly developing resistance against routinely used antimicrobials especially linezolid and chloramphenicol. Special surveillance to avoid injudicious used of these antimicrobials is the need of hour.