Susceptibility of human and probiotic Bifidobacterium spp. to selected antibiotics as determined by the Etest method

This study reports the antibiotic susceptibility of 203 strains representing human or probiotic associated Bifidobacterium species as determined by the Etest method. Strains showing minimum inhibitory concentration (MIC) for tetracycline ⩾16 μg mL−1 were detected in all studied Bifidobacterium species/groups (prevalence 4–18%). Mostly the high MICs could be associated with a tet gene, although the correspondence between the phenotypic susceptibility and detection of tet determinants was not complete. In addition to tet(W), tet(O), which has not been previously described in bifidobacteria, was detected. Occasional erythromycin (2%) and/or clindamycin (5%) resistant strains were found, while the strains were uniformly susceptible to ampicillin and vancomycin. Bifidobacterium strains displayed generally high MICs for streptomycin and gentamicin suggesting intrinsic resistance. The Etest on lactic acid bacteria susceptibility test medium supplemented with cysteine proved to be an applicable technique for antimicrobial susceptibility testing of bifidobacteria, and is especially useful when susceptibility data of individual strains is needed.