Antimicrobial susceptibility of Bifidobacterium.

The susceptibility pattern of 459 strains of bifidobacteria, representing 15 species, to 16 antimicrobial agents was determined by the broth dilution method. The majority of the strains derived from human faeces. Penicillin G, erythromycin, clindamycin, vancomycin and bacitracin were the most active compounds; they inhibited 90% of the strains at less than 1.6 micrograms/ml. All strains were susceptible to chloramphenicol (MIC90 = 2.0-5.8 micrograms/ml) and also to lincomycin (MIC50 = 0.64-1.5 micrograms/ml). Neomycin, streptomycin and tetracycline presented a great variability in their activity. Most strains were resistant to polymyxin B, nalidixic acid, kanamycin, gentamicin and metronidazole. The only variation in susceptibility which was observed among the different species concerned Bifidobacterium suis, which generally appeared to be more resistant than other species.