Cfr Gene-based Detection of Linezolid-Resistant Staphylococcus Aureus in a Tertiary Care Hospital in Western Uttar Pradesh, India

A BSTRACT Objective: Linezolid is an important antimicrobial agent which is active against multidrug-resistant Gram-positive cocci. Methicillin-resistant Staphylococcus aureus (MRSA) cause life-threatening infection, with narrow therapeutic options including linezolid and vancomycin. The presence of cfr (chloramphenicol–florfenicol resistance) and optr A (oxazolidinone phenicol resistance) gene plays a crucial role in linezolid resistance. Materials and Methods: A total of 199 clinical isolates were confirmed as S. aureus using GP ID p628 card, followed by antibiotic susceptibility testing using GPAST cards in the Vitek 2 compact system (Biomerieux, France) to determine minimum inhibitory concentration (MIC) of linezolid. An MIC value of ≥8 μg/ml was taken as resistant for linezolid. Furthermore, the presence of cfr and optr A gene was looked for in the clinical isolates of linezolid resistant S. aureus (LRSA). Results: LRSA was isolated in 2.5% of clinical samples. All LRSA were also MRSA, and all of them were recovered from indoor samples. The LRSA were 100% susceptible to vancomycin. cfr gene could be detected in 40% of the isolates. However, all our isolates of LRSA were negative for optr A gene. Conclusions: Emergence of linezolid resistance in clinical isolates of S. aureus is a matter of therapeutic concern which alerts toward judicious use of linezolid in clinical practice. The presence of cfr gene is the most common mechanism of resistance to linezolid.