ANTIBIOTIC SUSCEPTIBILITY OF POTENTIALLY PROBIOTIC BIFIDOBACTERIUM ISOLATES FROM THE HUMAN GASTROINTESTINAL-TRACT

Sixteen Bifidobacterium isolates from the human gastrointestinal tract were assayed for susceptibility to 44 antibiotics by soft agar overla y disc diffusion on TPY agar. Five isolates (3/7 B. bifidum and 2/3 B. breve) exhibited atypical antibiotic susceptibility profiles. Poor gr owth in the agar overlap accounted for susceptibility of B. bifidum bu t not B. breve isolates. All other isolates were resistant to cefoxiti n (30 mu g), aztreonam (30 mu g), vancomycin (30 mu g), amikacin (30 m u g), gentamicin (10 mu g), kanamycin (30 mu g), streptomycin (10 mu g ), fusidic acid (10 mu g), trimethoprim (5 mu g), norfloxacin (10 mu g ), nalidixic acid (30 mu g), metronidazole (5 mu g), polymyxin B (300 mu g) and colistin sulphate (10 mu g), and they were susceptible to th e six penicillins studied, cephalothin (30 mu g), cefuroxime (30 mu g) , cefaclor (30 mu g), ceftizoxime (30 mu g), cefotaxime (30 mu g), bac itracin (10 mu g), chloramphenicol (30 mu g), erythromycin (15 mu g), clindamycin (2 mu g), rifampicin (5 mu g) and nitrofurantoin (300 mu g ) In addition, they varied in their susceptibility to cephradine (30 m u g), cephazolin (30 mu g), cefoperazone (75 mu g), ceftriaxone (30 mu g), ofloxacin (5 mu g) and furazolidone (15 mu g). They were resistan t, or only marginally moderately susceptible, to ceftazidime (30 mu g) , netilmicin (10 mu g), sulphamethoxazole (100 mu g), cotrimoxazole (2 5 mu g) and ciprofloxacin (5 mu g), and susceptible or marginally mode rately susceptible to tetracycline (30 mu g). All B. bifidum isolates were susceptible to cefixime (5 mu g). Four microorganism-drug combina tions were evaluated for beta-lactamase activity but its absence sugge sted that cell wall impermeability was responsible for cephalosporin r esistance among bifrdobacteria. The antibiotic susceptibility of B. an imalis 25527T was similar to that of the human isolates.