Novel OXA-10-derived extended-spectrum beta-lactamases selected in vivo orin vitro

A clinical isolate of Pseudomonas aeruginosa, PAe191, was found to be highl y resistant to all anti-Pseudomonas beta-lactam antibiotics (except imipene m) and resistant also to aminoglycosides. It produced a beta-lactamase (wit h an apparent pI of 7.6) which was not inhibited by clavulanic acid. Clonin g and characterization of the beta-lactamase gene showed that it coded for a novel extended-spectrum OXA-10 variant, called OXA-19, which differed fro m OXA-10 by nine amino acids and from OXA-13 by two, i.e., Asn in position 73 (Asn73) instead of Ser and Asp157 instead of Gly. Asparagine in position 157 is implicated in resistance to ceftazidime, while the amino acid in po sition 73, in this variant, seems to condition the level of resistance to p enicillins. The oxa19 gene was found to be inserted, in a typical integron structure, immediately downstream from an aac(6')-Ib gene coding for an ami noglycoside acetyltransferase variant, which was called AAC(6')-Ib(9).