OXA-198, an Acquired Carbapenem-Hydrolyzing Class D β-Lactamase from Pseudomonas aeruginosa

A carbapenem-resistant Pseudomonas aeruginosa strain (PA41437) susceptible to expanded-spectrum cephalosporins was recovered from several consecutive lower-respiratory-tract specimens of a patient who developed a ventilator-associated pneumonia while hospitalized in an intensive care unit. Cloning experiments identified OXA-198, a new class D β-lactamase which was weakly related (less than 45% amino acid identity) to other class D β-lactamases. Expression in Escherichia coli TOP10 and in P. aeruginosa PAO1 led to transformants that were resistant to ticarcillin and showed reduced susceptibility to carbapenems and cefepime. The bla(OXA-198) gene was harbored by a class 1 integron carried by a ca. 46-kb nontypeable plasmid. This study describes a novel class D β-lactamase involved in carbapenem resistance in P. aeruginosa.