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Comparison of susceptibility testing methods for determining methicillin and linezolid resistance with meca and cfr gene prevalence among coagulase-negative staphylococci – a prospective study from south delhi

Authors:D Sharma , N Haque , A Das , A Lachyan
Int J Biol Med Res. 2024; 15(1): 7718-7723  |  PDF File

Abstract

Aims- This study accentuates surging methicillin and linezolid resistance among Coagulase Negative Staphylococcus (CoNS), correlating them with mec A and cfr gene presence respectively and focussing on a comparative analysis of various Antimicrobial Susceptibility tests (AST). Methods- This study was conducted at Department of Microbiology, HIMSR & HAHC hospital, Delhi from May 2020 –May 2021. The clinical samples from all age groups were cultured on appropriate culture media and the isolates were identified as CoNS as per standard norms, characterized on the basis of Novobiocin disc test. AST was performed on the isolates by automated method- VITEK-2, manual method – disc-diffusion method for cefoxitin and linezolid and by microbroth dilution for oxacillin. Additionally, status of mecA gene and cfr gene was determined by PCR. Results- Total 2150 clinical samples were collected of which 380 isolated tested positive for Staphylococcus. CoNS constituted 36.8% of these isolates. About 42.14% of CoNS isolates were from males and 57.85% were from females. Inpatient and Outpatient department contributed to 60% and 40% of the isolates respectively. Blood was the most frequent sample obtained (49%), followed by urine and pus (22.1%). Cefoxitin resistance was reported to be 87.14 % and 72.14% respectively by Kirby-Bauer method and VITEK 2. Oxacillin resistance was 80.71% by both Kirby-Bauer and microbroth dilution method and 80% by VITEK-2. However, mecA was only present in 62.85% of the total isolates. Linezolid resistance was 2.85 % and 2.14 % respectively by Kirby-Bauer and VITEK-2 methods. None of the isolates harboured cfr gene. Discussion- Cefoxitin proved as a better marker of mec A gene in contrast to oxacillin. The cefoxitin Disc-diffusion method is considered a better predictor for the detection of heterogeneous methicillin resistance. Considering the fact that methicillin resistance has gravely escalated in CoNS, the need for new treatment options is now a necessity.