Antimicrobial susceptibility of bifidobacteria

Objectives: The aim of our study was to analyse the antibiotic susceptibility of various strains of Bifidobacterium spp. to a wide range of antimicrobial agents. Methods: Fifty strains belonging to eight species of bifidobacteria, isolated from humans, animals or probiotic products, were tested for susceptibility to 30 antibiotics by disc diffusion on Brucella agar supplemented with 5 % laked sheep blood and vitamin K1 (1 mg/L). MICs of nine anti-anaerobe agents, including three new molecules (telithromycin, linezolid and gatifloxacin), were determined using the reference agar-dilution method. Results: All strains of bifidobacteria, whatever the species, were sensitive to penicillins: penicillin G, amoxicillin (MIC50 0.06 mg/L), piperacillin, ticarcillin, imipenem and usually anti-Gram-positive anti-biotics (macrolides, clindamycin, pristinamycin, vancomycin and teicoplanin). Susceptibility to cefa-lothin and cefotetan was variable. Most isolates (70%) were resistant to fusidic acid. As expected, high resistance rates were observed for aminoglycosides. Metronidazole, an agent known for its anti-anaerobe activity, was ineffective against 38 % of the strains. The newly commercialized molecules, telithromycin, linezolid and gatifloxacin, were active with MIC50S of 1 mg/L. The only variation in sus-ceptibility observed among the different species concerned Bifidobacterium breve, which appeared t