Laurence R. McCarthy

Penicillinase activity in three strains ofClostridium butyricum

Three strains ofClostridium butyricum exhibited elevated minimal inhibitory concentrations (MICs) to penicillin (64–1,024 μg/ml), ampicillin (32–256 μg/ml), carbenicillin (128–1,024 μg/ml), and oxacillin (32–64 μg/ml). Cephalosporin/cephamycin agents were more active than penicillin drugs. All isolates were found to possess a β-lactamase. The β-lactamases were primarily cell associated during the logarithmic phase of growth. Stationary-phase cells released most of the enzyme into the culture medium. Cephalothin supplementation of broth cultures with concentrations equivalent to one-eighth of the MIC significantly increased the quantity of β-lactamase synthesized. The β-lactamases produced by these three isolates exhibited greatest activity with penicillin followed by ampicillin>cephaloridine>carbenicillin and oxacillin. No enzymatic activity was observed using cephalothin, cephalexin, cefazolin, cefoxitin, or cephamandole substrates. The β-lactamases were inhibited by clavulanic acid and para-chloromurcuribenzoate and not inhibited by cloxacillin. Each enzyme exhibited an isoelectric point of 4.2.

Further studies of the β-lactamases ofBacteroides species

The β-lactamases of individual strains ofBacteroides fragilis, B. thetaiotaomicron, andB. melaninogenicus were examined to characterize their enzymatic activity and the relation between the periplasmic and cytoplasmic forms of the enzymes. Km and Vmax values indicate that all strains examined were very similar in terms of enzymatic activity with the antibiotics tested. Electrophoretic analysis and treatment with phospholipase D suggest the presence of a cytoplasmic form of the enzyme that is modified upon entry into the periplasmic space.

Comparison of the β-lactamases ofBacteroides species

Abstractβ-Lactam antibiotic susceptibility and the presence of β-lactamase were examined in clinical strains ofBacteroides species. All strains produced a noninducible, cell-associated cephalosporinase. Based on isoelectric focusing, molecular weight determinations, substrate profiles, and inhibition studies, it was concluded that allBacteroides strains examined produced a very similar, if not identical, β-lactamase in terms of these enzymatic and physical characteristics.