Emergence of Chloramphenicol-florfenicol resistance (cfr) gene mediated linezolid resistance in methicillin resistant Staphylococcus aureus, case reports and review of literature.

Context: Despite the use of linezolid, resistance to it has remained stable and extremely low with only sporadic cases have been reported. Aim: To find out linezolid resistance in MRSA isolates. Material and Methods: Specimens were collected aseptically and cultured using standard microbiological protocols. Antibiotic susceptibility was done by Kirby-Bauer disc diffusion method according to CLSI guidelines. Minimum inhibitory concentration (MIC) of these isolates were carried out and confirmed by E-test. PCR was performed for mec A, nuc A and cfr genes. Sequencing of the linezolid resistant isolates was also carried out. Results: We here report three cases of cfr mediated linezolid resistant MRSA isolated from patients. MIC of linezolid to each Staphylococcus aureus was ?8 µg/ml. The MIC of linezolid was further confirmed by E –test. PCR was done for amplification of mec A, nuc A and cfr genes confirming MRSA and cfr mediated linezolid resistance. Conclusion: Scarcity of newer antimicrobials and increasing resistance to available drugs demands implementation of infection control measures to prevent the dissemination of cfr gene mediated linezolid resistant Staphylococcus aureus.