Isolation, identification, and antibiotic susceptibility of nis+ Lactococcus lactis from dairy and non-dairy sources.

Eight isolates of Lactococcus lactis subsp. lactis were isolated and identified by phenotypic and molecular characterisation out of 23 isolates of lactic acid bacteria (LAB) from different dairy and non-dairy sources. Out of eight strains, four were obtained from dairy and four from non-dairy sources. All eight strains of L. lactis subsp. lactis were able to produce zones of inhibition against the Lactobacillus acidophilus NCDC 015. The antimicrobial agent produced by the isolates inhibited the growth of a range of related lactic acid bacteria and certain Gram positive food-borne microorganisms. The antimicrobial agent, i.e. nisin, produced by the strains was confirmed by PCR amplification of nisin gene sequences of 174 bp size. Antibiotic susceptibility test to 21 different types of antibiotics was evaluated. All the isolates were resistant to fosfomycin, cefepime, amikacin, kanamycin, neomycin, nalidixic acid, pipemidic acid, norfloxacin, sulphadiazine, colistin, polymixin, teicoplanin, nystatin, and amphotericin B but susceptible to ampicillin, erythromycin, spiramycin, spectinomycin, ciprofloxacin, rifampicin, and trimethoprim.