Biochemical-Genetic Characterization of the Chromosomally Encoded Extended-Spectrum Class A β-Lactamase from Rahnella aquatilis

From whole-cell DNA of a clinical isolate of the enterobacterial species Rahnella aquatilis, a β-lactamase gene was cloned that encoded a chromosomally encoded Ambler class A enzyme, RAHN-1. RAHN-1, with a pI of 7.2, shares 76, 73, and 71% amino acid identity with the extended-spectrum β-lactamase of chromosomal origin from Serratia fonticola and with the plasmid-mediated β-lactamases CTX-M-2 and CTX-M-1, respectively. The hydrolysis spectrum of the clavulanic acid-inhibited RAHN-1 was expanded to cephalosporins such as cefuroxime, cefotaxime, and ceftriaxone, but not to ceftazidime. Its expression was not inducible.