Biochemical-Genetic Characterization and Distribution of OXA-22, a Chromosomal and Inducible Class D β-Lactamase from Ralstonia (Pseudomonas) pickettii

From genomic DNA of Ralstonia pickettii isolate PIC-1, a β-lactamase gene was cloned that encodes the oxacillinase OXA-22. It differs from known oxacillinases, being most closely related to OXA-9 (38% amino acid identity). The hydrolytic spectrum of OXA-22 is limited mostly to benzylpenicillin, cloxacillin, and restricted-spectrum cephalosporins. OXA-22-like genes were identified as single chromosomal copies in five other R. pickettii clinical isolates. The expression of OXA-22-like β-lactamases was inducible in R. pickettii.