Characterization of the chromosomal cephalosporinases produced by Acinetobacter Iwoffii and Acinetobacter baumannii clinical isolates

The β-lactamases produced by Acinetobacter Iwoffii ULA-501, Acinetobacter baumannii ULA-187, and A. baumannii AC-14 strains were purified and characterized, and their kinetic interactions with several β-lactam molecules, including substrates and inhibitors, were studied in detail. The three enzymes appeared to be cephalosporinases with different acylation efficiencies (kcat/Km ratio values), and their hydrolytic activities were inhibited by benzylpenicillin, piperacillin, and cefotaxime, which did not behave as substrates. Carbenicillin was a substrate for the β-lactamase from A. Iwoffii ULA-501, whereas it acted as a transient inactivator of the enzymes produced by the two A. baumannii strains. Clavulanic acid was unable to inactivate the three β-lactamases, whereas sulbactam behaved as an inactivator only at a high concentration (1 niM) which is difficult to achieve during antibiotic therapy. Analysis of the interaction with 6-β-iodopenicillanic acid also allowed us to better discriminate the three β-lactamases analyzed in the present study, which can be included in the group 1 functional class (5).