Emergence of antimicrobial resistance and virulence factors among the unusual species of enterococci, from North India.

Abstract

Several enterococcal species are increasingly being reported from clinical infections, besides the major species. This study was undertaken to determine the prevalence of unusual enterococcal species and their antimicrobial susceptibility patterns, virulence factors, and molecular characterization. The study was conducted in Department of Microbiology and associated Tertiary Care University Hospital in North India. Enterococcal isolates were collected for a period of 2 years from clinical specimens. Identification and elaborate phenotypic characterization was done biochemically. All the isolates were tested by Kirby-Bauer disc diffusion method and breakpoint minimum inhibitory concentration for susceptibility against standard antibiotics. Screening for vancomycin-resistant enterococci (VRE), high-level aminoglycoside resistance was done on brain heart infusion agar incorporated with 6 μg/ml vancomycin, 500 μg/ml gentamicin, and 2000 μg/ml streptomycin, respectively. VRE isolates were tested for the presence of vanA, vanB, and vanC genes and high-level gentamicin resistant (HLGR) isolates for aac-6'- aph-2' gene by polymerase chain reaction (PCR). Hemolysin and gelatinase production, hemagglutination and biofilm formation were detected along with asa1, gelE, esp, hyl, and cylA genes by multiplex PCR. Of 403 enterococci, 93 (23.07%) isolates were identified as unusual species and atypical variants. Resistance of 52.68%, 46.23%, 44.08%, and 6.45% for ampicillin, ciprofloxacin, high strength gentamicin, and vancomycin, respectively were noted. Presence of vanC gene in Enterococcus gallinarum and Enterococcus casseliflavus isolates and vanA gene in Enterococcus durans and Enterococcus hirae and aac-6'- aph-2'' gene was found in 33.14% (14/41) of the HLGR isolates. The most frequent virulence factor was biofilm production. Only a few isolates harbored asa1 (2), gelE (9), and hyl (3) genes. Considerable prevalence of pathogenic unusual species of enterococci was seen along with their emerging drug resistance and virulence. Complete identification and routine speciation is essential to limit their emergence as major species in near future.