Enzymatic and Immunological Characterization of a New Cephalosporinase from Enterobacter aerogenes

A hospital strain of Enterobacter aerogenes (MULB 250) isolated from a urinary tract infection was found to be cephalosporin and ampicillin resistant and carbenicillin susceptible. The β-lactamase produced by this strain was extracted and purified by means of affinity chromatography, using a cephalosporin C-bound Sepharose 4B column. The purified enzyme was tested for hydrolysis of penicillin and various cephalosporins. The K_m value is 11.8 μM for benzyl penicillin and 130 μM for cephalosporin C. The isoelectric point of the enzyme is 9.3, and its molecular weight is 29,500 ± 1,000. Rabbit antiserum obtained against this MULB 250 β-lactamase showed no cross-reaction with other penicillinases or cephalosporinases in neutralization tests. Comparisons of results obtained with other β-lactamases, particularly from Enterobacter cloacae P99, indicate that the Enterobacter MULB 250 enzyme presents a typical cephalosporinase profile. As far as we know, this type of enzyme is relatively rare.