Comparison of Vancomycin MICs by Broth Microdilution Method, E-Test and Vitek 2C among MRSA Isolates in Tertiary Care Centre, Hyderabad, India

Introduction: The most important pathogen isolated from Skin and Soft Tissue Infections (SSTIs) is a Gram positive organism, Staphylococcus aureus (S.aureus). Wide range of emerging Methicillin Resistant Staphylococcus aureus (MRSA) infections is leading to global threat causing Community Acquired-MRSA (CA-MRSA) or Hospital Acquired MRSA (HA-MRSA). Minimum Inhibitory Concentration (MIC) is done to ensure that antibiotics are chosen efficiently in the clinical settings by Vitek 2, Epsilometer- test (E-test) and Broth Microdilution (BMD) method. Aim: To determine the clinical spectrum of MRSA and comparison of Vancomycin MICs obtained by E-test, Vitek 2C and BMD method. Materials and Methods: This was a cross-sectional study that was conducted at Nizam’s Institute of Medical Sciences, Hyderabad, Telangana, India during the period of November 1st 2019 to December 31st, 2020 from Inpatient Department (IPD) and Outpatient Department (OPD). Among 464 SSTIs, 132 were S.aureus, out of which 38 isolates were MRSA. Identification and sensitivity of the isolates such as pus, wound swabs, and tissues were identified through Vitek 2 compact system. Statistical analysis of the demographic and clinical characteristics was represented as frequency and percentages. Results: A total of 464 SSTIs, S.aureus were 132 of which MRSA were 38 (29%) and Methicillin sensitive Staphylococcus aureus (MSSA) were 94 (71%) with male predominance of 29 (76.3%) with MRSA. Most of the patients were in the age group of 21- 30 years (26%). Amongst the total 38 patients analysed,25 were from IPD and 13 were from OPD. A 23/38 wound swabs (60%) 12/38 of pus (28%) and 3/38 (7%) were tissues. The predominant risk factor observed was Surgical Site Infections (SSI) in 19 cases (50%) followed by prior antibiotic therapy in 17 (44%) cases. The median duration of hospitalisation was 31.5 days. Vancomycin susceptibility by all three methods with an MIC range of 0.5-2μg/ ml by all three methods, except for one isolate where the MIC was >32ug/ml by Vitek 2C and 8 ug/mL by E-test, which was sensitive by BMD with an MIC of 0.25 μg/mL. Conclusion: Implementing infection control practices and controlling the risk factors will help in management of MRSA infections. Drug resistance to Glycopeptides can be avoided by regular screening of vancomycin creeps by different susceptibility methods in order to avoid treatment failures.