Determination of minimum inhibitory concentration of vancomycin by agar dilution method for detection of vancomycin resistant enterococci isolated from various clinical specimens

Background: Enterococci plays an important role in nosocomial infections and also become resistant to a variety of antimicrobials through intrinsic and acquired mechanisms. Emergence of Vancomycin Resistant Enterococci (VRE) has possessed a greater threat in its treatment. Detection of MIC of Vancomycin is important to treat VRE. Objective: To determine the prevalence and the antibiotic susceptibility pattern of Enterococci isolated from various clinical specimens & to determine the MIC of VRE by agar dilution method in our institute. Material And Methods: The study was conducted at the Department of Microbiology at Shridevi Institute of Medical Sciences & Research Hospital over a period of one year from June 2022 to July2023. All the enterococci obtained from urine, pus, blood and body fluids were included in the study. The isolates were confirmed and speciation was done by arginine deamination and fermentation of arabinose, mannitol, raffinose, and sorbitol. Antimicrobial susceptibility was determined by Kirby Bauer disk diffusion .MIC of vancomycin was determined by agar dilution method for all the enterococci isolates which showed intermediate and resistance to Vancomycin by Kirby Bauer disc diffusion method. Results: Amongst the total 60 Enterococcal isolates, 37 isolates (61.66 %) were Enterococcus faecalis, 23 isolates (38.33%) were Enterococcus faecium. Out of the 60 isolates, 28 (46.66%) were from pus followed by 22 (36.66%) were from urine, 9 (15 %) from blood, 1(1.66%) from pleural fluid. Antibiotic susceptibility pattern of Enterococci showed high sensitivity Teicoplanin 59(98.33 %) followed by Linezolid 55(91.66%) and High-level Gentamicin 47(78.33%).Out of the 11 isolates intermediate or resistant to vancomycin by Kirby Bauer disc diffusion method, 10 were sensitive by agar dilution method, whereas the only one isolate was resistant with MIC of 32 μg/ml .Occurrence of VRE in our setting is 1.6 %. Conclusion: Disk diffusion testing for vancomycin in enterococci can be unreliable and requires confirmation by an MIC method. Early detection, treatment and preventive action will help to limit the serious consequences caused by vancomycin resistant enterococcal infection