Purification and Properties of Chromosomally Mediated -Lactamase from Citrobacter freundii GN7391

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Abstract
Both a penicillinase and a cephalosporinase are present in a strain of C. freundii (GN7391) resistant to .beta.-lactam antibiotics. The penicillinase was identical to the type Ia penicillinases (Type III by Richmond classification), mediated by Rms212 and R-TEM. A cephalosporinase, typical of enterobacteriaceae chromosomal .beta.-lactamase (Type I by Richmond classification), was purified from the strain. It gave a single protein band on polyacrylamide gel electrophoresis and immunoelectrophoresis; the pI [isoelectric point] was 8.6 and its MW was .apprx. 38,000. Cysteine was not found among its amino acids. The specific activity was 388 U/mg protein for the hydrolysis of cephaloridine, and the optimal pH was 8.0. Rabbit antiserum obtained against the purified enzyme showed cross-reaction with cephalosporinases produced by strains of Enterobacter cloacae in a neutralization test.