Phenotypic and genotypic characterization of antimicrobial resistance in Enterococcus species from dairy niches

Abstract

The present work was carried out to investigate the prevalence of antimicrobial resistance (AMR) in dairy enterococci. Dairy samples comprising of raw milk and traditionally fermented milks were collected from local surrounding areas and a total of 140 enterococci strains were isolated from the dairy samples and further, 104 isolates were tested for antimicrobial susceptibility. The most prevalent resistance was observed against cephalosporins followed by fosfomycin, rifampicin, erythromycin etc. Multi-antibiotic resistance index of the tested isolates ranged from 0.09 to 0.36. Minimum inhibitory concentration testing showed very high cut-offs against erythromycin, tetracycline, cefepime and cefotaxime in certain isolates. Further, Extended Spectrum β-lactamase (ESBL) production tested by double disc synergy method confirmed 9 isolates as ESBL positive along with the presence of blaTEM gene in certain isolates. In addition, AMR genes against aminoglycoside, tetracyclines, macrolides, chloramphenicol along with multi-drug transporter gene (emeA) was also detected in many isolates. The resistant enterococci isolates also showed a high frequency of the presence of mobile genetic elements viz. Transposons (Tn-5397 and Tn-916/Tn-1545 family) and Integrons (intI1, intI3). Finally, virulence traits such as gelatinase and hemolysin production along with gelE and cylA genes was also detected in many of the resistant enterococci isolates. Although, the virulence traits could not be directly correlated with the AMR resistance of the isolates, the results from the study demonstrated the wide prevalence of AMR in dairy enterococci that could greatly contribute to the problem of antimicrobial resistance in the food chain.