Antibiotic susceptibility profiles of new probiotic Lactobacillus and Bifidobacterium strains

The antimicrobial susceptibilities and presence of plasmids in four new probiotic lactic acid bacteria (LAB) strains, Lactobacillus rhamnosus HN001 (DR20™) HN067, Lactobacillus acidophilus HN017 and Bifidobacterium lactis HN019 (DR10™), were determined. Resistance to 18 commonly used antibiotics was assessed by disk diffusion. The three Lactobacillus strains had similar antibiotic susceptibility profiles to those of Lactobacillus plantarum strain HN045 and two commercial probiotic Lactobacillus strains, GG and LA-1. The B. lactis strain HN019 had a similar profile to three commercial probiotic B. lactis strains (Bb12, HN049 and HN098). All 10 strains were sensitive to the Gram-positive spectrum antibiotics erythromycin and novobiocin, the broad-spectrum antibiotics rifampicin, spectinomycin, tetracycline and chloramphenicol and the β-lactam antibiotics penicillin, ampicillin and cephalothin. By contrast, most strains were resistant to the Gram-negative spectrum antibiotics fusidic acid, nalidixic acid and polymyxin B and the aminoglycosides neomycin, gentamicin, kanamycin and streptomycin. All three L. rhamnosus strains (HN001, HN067 and GG) were resistant to vancomycin and several strains were also resistant to cloxacillin. Of the four new probiotic strains, only L. rhamnosus HN001 contained plasmids; however, a plasmid-free derivative of HN001 had the same antibiotic susceptibility profile as the parent strain.