Linezolid and Vancomycin Resistant Enterococci: A Therapeutic Problem

Introduction: Enterococci are recognized as opportunistic pathogens, as well as commensals in both humans and animals. They are an important cause of nosocomial infections, difficult to treat, as the organism have intrinsic and acquired resistance to many antibiotics.

Aim: To isolate and identify clinically relevant up to species level from all the clinical samples processed in the microbiology laboratory and also to study their resistance pattern.

Materials And Methods: A prospective study was carried out for a period of one year from May 2014 to April 2015 at the Department of Microbiology, Subharti Medical College, Meerut, Uttar Pradesh, India. A total of 200 isolates of species from 15342 clinical samples obtained from IPD/OPD patients irrespective of age, having suspicion of bacterial infection were processed in the microbiology laboratory. Identification was done with standard biochemical methods. Antibiotic susceptibility testing was done on Muller Hilton agar plate by Kirby Bauer disc diffusion method. High-Level Gentamycin Resistance (HLGR) and High-Level Streptomycin Resistance (HLSR) were further confirmed by Agar dilution method and Broth microdilution method. Vancomycin and linezolid resistance was further confirmed by Agar dilution method and MIC was calculated by using VITEK 2, Biomerieux. All methodology was followed as per Clinical and Laboratory Standards Institute (CLSI) M100-S 24, 2014 guidelines.

Results: (n=169, 84.5%) was the predominant species isolated, followed by (n=27, 13.5%) and (n=4, 2%). A total of 25 (12.5%) isolates were HLGR, 13 (6.5%) isolates were HLSR and 62 (31%) isolates were HLGR+HLSR. Vancomycin resistance was found in 14 (7%) isolates of which 11 (78.5%) were Van A and 3 (21.4%) were Van B, detected phenotypically as per relative MIC of vancomycin and teicoplanin. Linezolid resistance was seen in 4 (2%) of isolates which were vancomycin as well as high-level gentamycin and high-level streptomycin resistant.

Conclusion: Isolation of species resistant to most of the higher antibiotics like vancomycin and linezolid, with high prevalence of High-Level Aminoglycoside Resistance (HLAR), from hospitalized patients is a major concern as such isolates have limited or no therapeutic option.