Seven beta-lactamase-producing Fusobacterium nucleatum strains were isolated from patients with recurrent tonsillitis. The isolates were highly resistant to phenoxymethylpenicillin, benzylpenicillin, ampicillin, piperacillin and cloxacillin. They were all sensitive to cefaclor, cephaloridine, cefotaxime, cefoxitin, latamoxef (moxalactam) and imipenem. Penicillinase activity was found intracellularly after 20 h incubation. Specific activity of the unpurified penicillinase varied among the strains between 0. 24-9. 3 U/mg protein. The enzyme hydrolysed ampicillin and benzylpenicillin more rapidly than piperacillin. Cephalothin and imipenem were hydrolysed at rates less than 1% of benzylpenicillin. Chromatofocusing experiments eluted the beta-lactamases from all strains at a single peak between pH 5. 1-5. 2 VSports手机版. .