TLA-1: a new plasmid-mediated extended-spectrum beta-lactamase from Escherichia coli

Escherichia coli R170, isolated from the urine of an infected patient, was resistant to expanded-spectrum cephalosporins, aztreonam, ciprofloxacin, an d ofloxacin but was susceptible to amikacin, cefotetan, and imipenem. This particular strain contained three different plasmids that encoded two beta- lactamases with pIs of 7.0 and 9.0. Resistance to cefotaxime, ceftazidime, aztreonam, trimethoprim, and sulfamethoxazole was transferred by conjugatio n from E. coli R170 to E. coli J53-2. The transferred plasmid, RZA92, which encoded a single beta-lactamase, was 150 kb in length. The cefotaxime resi stance gene that encodes the TLA-1 beta-lactamase (pI 9.0) was cloned from the transconjugant by transformation to E. coli DH5 alpha. Sequencing of th e bla(TLA-1) gene revealed an open reading frame of 906 bp, which correspon ded to 301 amino acid residues, including motifs common to class A beta-lac tamases: (SXXK)-S-70, (SDN)-S-130 and (234)KTG. The amino acid sequence of TLA-1 shared 50% identity with the CME-1 chromosomal class A beta-lactamase from Chryseobacterium (Flavobacterium) meningoseptiegm; 48.8% identity wit h the VEB-1 class A beta-lactamase from E. coli; 40 to 42% identity with Cb lA of Bacteroides uniformis, PER-1 of Pseudomonas aeruginosa, and PER-2 of Salmonella typhimurium; and 39% identity with CepA of Bacteroides fragilis. The partially purified TLA-1 beta-lactamase had a molecular mass of 31.4 k Da and a pi of 9.0 and preferentially hydrolyzed cephaloridine, cefotaxime, cephalothin, benzylpenicillin, and ceftazidime. The enzyme was markedly in hibited by sulbactam, tazobactam, and clavulanic acid, TLA-1 is a new exten ded-spectrum beta-lactamase of Ambler class A.