Characterization of Antibiotic Resistance in Dairy Lactococci

Abstract

The present study was carried out to check the prevalence of antibiotic resistance amongst the dairy lactococci strains. A total of 65 lactococcal strains were isolated from dairy samples such as cheese, raw milk, local market milk etc. Further, 34 unique strains alienated from typical RAPD profiles were subjected to antibiotic resistance testing by disc diffusion method against a total of 23 clinically relevant antibiotics. Most of the isolates were found to exhibit resistance against commonly used antibiotics such as trimethoprim, aminoglycosides, quinolones, and some of the β-lactams groups of antibiotics. Variable resistance against Lincosamides, Bacitracin, Novobiocin, Teicoplanin, Erythromycin and Tetracycline were observed. However, all the isolates were susceptible to Ampicillin and Vancomycin (except one). Isolates exhibiting resistance to as many as 18 antibiotics out of 23 tested antibiotics were also observed in the study. Minimum inhibitory concentration (MIC) using broth microdilution method was also performed for 14 highly resistant isolates. The results of the disc diffusion method correlated well with the broth microdilution method and all strains exhibited MIC values for ampicillin within the breakpoint. However, all strains crossed the MIC breakpoints for kanamycin and streptomycin, and majority of the isolates for gentamycin and clindamycin. Comparatively lower numbers of strains were seen to cross the microbiological breakpoints for Chloramphenicol, Erythromycin and Tetracycline. The study clearly demonstrates the prevalence of high level of antibiotic resistance in dairy lactococci, which hints us to more careful use of these bacteria in food and feed industry.