Characterization of a new plasmid-mediated extended-spectrum beta-lactamase from Serratia marcescens

A new extended spectrum beta-lactamase was detected in Serratia marcescens 42039 that was isolated from urine of patients with complicated urinary tract infection in Japan. This strain produced three different beta-lactamase types (TEM-1, a cephalosporinase, and a new beta-lactamase: CKH-1). The TEM-1 and CKH-1 encoding genes were conjugated from S. marcescens 42039 to Escherichia coli K-12 at frequencies of 10(-5) to 10(-6). The MICs of beta-lactams against the transconjugant were: ampicillin >1600, piperacillin 800, cephalothin 1600, ceftazidime 6.25, cefotaxime 100, and ceftriaxone 200 mu g/ml. The CKH-1 enzyme was purified to more than 90% by ion-exchange chromatography. The molecular weight of purified CKH-1 was 30 K dalton and the isoelectric point was 8.2. Relative Vmax/Km values (cephaloridine=100) of penicillin G, cephalothin, and oxyiminocephalosporins such as cefuroxime, ceftriaxone, and cefotaxime, were 256, 226, 116, 87, and 49, respectively. The I-50 values of tazobactam, BRL-42715, and clavulanic acid against CKH-1 enzyme were 0.0011, 0.0002, and 0.097 mu M, respectively. The enzymatic activity of CKH-1 was not inhibited by EDTA and anti-TEM-1 serum. These findings indicate that CKH-1 is a member of the groups of class A beta-lactamases. This is the first report of a plasmid-mediated oxyiminocephalosporin hydrolyzing broad-spectrum beta-lactamase from clinical isolates of S. marcescens.