Susceptibility of bifidobacteria originating from different sources to tetracycline, erythromycin, streptomycin and vancomycin

MIC distributions of 365 Bifidobacterium spp. strains were determined for tetracycline, erythromycin,streptomycin and vancomycin. Susceptibility testing was performed either by Etest or broth microdilution (MDIL) using VetMIC panels. The tetracycline susceptible wild type population isolates of the human/probiotic Bifidobacterium spp., tested b Etest, had MICs ≤1 µg/ml (B. adolescentis group, B. bifidum, B. catenulatum) or ≤ 4 µg/ml (B. longum group). All tetracycline susceptible wild type populations of the animal bifidobacteria, tested by broth microdilution, had MICs ≤ 4 µg/ml (B.pseudolongum) or ≤ 8 µg/ml (B. thermophilum). Acquired resistance to erythromycin was rare in bifidobacteria. B. adolescentis group, B. bifidum and B. pseudolongum showed a unimodal distribution consisting of only susceptible wild type population (cut-offs ≤ 0.25 µg/ml, ≤ 0.12 µg/ml, and ≤ 0.5 µg/ml, respectively). Eleven potentially erythromycin resistant strains representing B. animalis, B. longum group, B. catenulatum group and B. thermophilum were detected (cut-off for the groups being ≤ 0.25 µg/ml, ≤ 0.25 µg/ml, ≤ 0.25 µg/ml, and ≤ 1 µg/ml, respectively). All studied Bifidobacterium species/groups were intrinsically resistant to streptomycin and susceptible to vancomycin (cut-offs for B. adolescentis group, B. catenulatum group, B. animalis strains being ≤ 1 µg/ml, for B. longum group and B. bifidum ≤ 2 µg/ml, and for B. thermophilum, B.pseudolongum ≤ 1 µg/ml vancomycin).