A STUDY ON EVALUATION OF LABORATORY DETECTION METHODS AND PREVALENCE RATE OF VANCOMYCIN HETERORESISTANCE IN CLINICAL ISOLATES OF STAPHYLOCOCCUS AUREUS IN A TERTIARY CARE HOSPITAL

INTRODUCTION: Staphylococcus aureus plays an important role in cause of many infections. Methicillin resistant Staphylococcus aureus are resistant to βlactamase inhibitor and penicillinase resistant penicillins where Vancomycin has been the treatment of choice, nowdays showing clinical failure due to hVISA defined as Staphylococcus aureus with a vancomycin MIC within susceptible range when tested by routine methods (vancomycin broth dilution MIC≤2μg/ml)but where a proportion of cells are in vancomycin intermediate range. AIM OF THE STUDY: Detection of vancomycin heteroresistance among Staphylococcus aureus isolates and to evaluate the various laboratory detection methods for vancomycin heteroresistance in Staphylococcus aureus. MATERIALS AND METHODS: During the period of October 2015-september 2016, 100 nonduplicate, significant MRSA isolates are screened for vancomycin heteroresistance by vancomycin screen agar, Broth Microdilution, Estrip GRD and confirmed by population analysis profile method. RESULTS: Among 100 isolates, by vancomycin screen agar method heteroresistance was detected in 5 isolates as demonstrated by presence of growth at 48hrs ; 48 isolates showed vancomycin MIC as 1μg/ml by BMD method and 3 MRSA isolates had MIC 4μg/ml that were identified as VISA according to CLSI breakpoints 2016. By E strip GRD most of the isolates shows MIC ≤2μg/ml for vancomycin (98%) and teicoplanin (94%) and 2/100 isolates are identified as VISA .By gold standard Modified population analysis profile the PAP-AUC curve cut off result was ≥0.9 for 3 isolates that are confirmed to be hVISA. CONCLUSION: All screening methods revealed fair good specificity than sensitivity. From this study, it was concluded that using vancomycin screen agar combined with BMD is effective approach for screening vancomycin heteroresistance among staphylococcus aureus isolates and Modified PAP-AUC is the only gold standard method for confirmation of hVISA isolates and its prevalence rate is 3% among MRSA.