A CLINICAL ISOLATE OF AEROMONAS-SOBRIA WITH 3 CHROMOSOMALLY MEDIATED INDUCIBLE BETA-LACTAMASES - A CEPHALOSPORINASE, A PENICILLINASE AND A 3RD ENZYME, DISPLAYING CARBAPENEMASE ACTIVITY

Hydrolytic profiles of Aeromonas sobria 163a, non-induced and induced, and of a derepressed mutant 163a-M, indicate that this strain has ind ucible beta-lactamases with activities against cephalosporins, penicil lins and carbapenems. Three enzymes were identified and two of the bet a-lactamase genes, ampS, encoding a penicillinase and cepS, encoding a cephalosporinase, were cloned into Escherichia coli, permitting analy sis of the individual, enzymes. Isoelectric focusing (IEF) analysis us ing inhibition profiles with EDTA anti BRL 42715, confirmed AmpS (pI 7 .9) and CepS (7.0) to be serine beta-lactamases. A third beta-lactamas e displaying hydrolytic activity against the carbapenems was inhibited by EDTA. The carbapenemase had a pI of 9.3 and was detected on IEF ge ls by overlaying the gel with agarose containing imipenem and the chro mogenic pH indicator, bromothymol blue. Co-inducibility and the recove ry of a derepressed mutant in which all three enzymes were produced at high levels indicate that this isolate of A. sobria has three co-ordi nately controlled beta-lactamase genes.