Biochemical-genetic characterization of the chromosomally encoded extended-spectrum class a beta-lactamase from Rahnella aquatilis

From whole-cell DNA of a clinical isolate of the enterobacterial species Ra hnella aquatilis, a beta -lactamase gene was cloned that encoded a chromoso mally encoded Ambler class A enzyme, RAHN-1. RAHN-1, with a pI of 7.2, shar es 76, 73, and 71% amino acid identity with the extended-spectrum 13-lactam ase of chromosomal origin from Serratia fonticola and with the plasmid-medi ated beta -lactamases CTX-M-2 and CTX-M-1, respectively. The hydrolysis spe ctrum of the clavulanic acid-inhibited RAHN-1 was expanded to cephalosporin s such as cefuroxime, cefotaxime, and ceftriaxone, but not to ceftazidime. Its expression was not inducible.