Cephalosporinase activity in Bacteroides fragilis.

Cephalosporinase activity was demonstrated in all of 10 strains of Bacteroides fragilis investigated. Low rates of hydrolysis of cephalosporins (0.25 to 3.5 mumol of cephaloridine per h per 10(9) cells) were found, but no activity against penicillin substrates was detected. In two strains the cephalosporinase activity was increased 40-and 80-fold by growing cells in the presence of penicillin. No permeability barrier for these antibiotics was demonstrated. In most cases the substrate profile showed decreasing activity in the following order: cephaloridine > cephalothin > cephaloglycin > cephalexin. The cephalosporinase from these organisms differed from that found in facultative and aerobic gram-negative bacilli in that it was inhibited by both cloxacillin and p-chloromercuribenzoate. Among nine strains of Bacteroides fragilis subspecies fragilis, correlation was found between in vitro resistance to cephaloridine and amount of beta-lactamase activity in sonically disrupted cells.