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. 1998 Aug;42(8):1980-4.
doi: 10.1128/AAC.42.8.1980.

CTX-M-5, a novel cefotaxime-hydrolyzing beta-lactamase from an outbreak of Salmonella typhimurium in Latvia

P A Bradford  1 , Y Yang, D Sahm, I Grope, D Gardovska, G Storch
Affiliations

CTX-M-5, a novel cefotaxime-hydrolyzing beta-lactamase from an outbreak of Salmonella typhimurium in Latvia

P A Bradford et al. Antimicrob Agents Chemother. 1998 Aug.

Abstract

At a children's hospital in Riga, Latvia, isolates identified as Salmonella typhimurium were found to be resistant to expanded-spectrum cephalosporins. Two of the resistant strains were analyzed for the mechanism of cephalosporin resistance. Isoelectric focusing revealed a common beta-lactamase with a pI of 8.8. In addition, one of the strains produced a pI 7.6 beta-lactamase. A transconjugant producing only the pI 7.6 enzyme was susceptible to expanded-spectrum cephalosporins; therefore, this enzyme was most likely SHV-1. Transformants producing only the pI 8.8 beta-lactamase were resistant to cefotaxime and aztreonam but were susceptible or intermediate to ceftazidime. A substrate profile determined spectrophotometrically with purified enzyme revealed potent activity against cefotaxime, with a relative kcat value of 95 (benzylpenicillin equal to 100). The enzyme showed lower relative kcat values for ceftazidime (3.3) and aztreonam (9.3). In addition, the enzyme was inhibited by clavulanate, sulbactam and tazobactam, with 50% inhibitory concentrations of 19, 100, and 3.4 nM, respectively. These results indicated the presence of an unusual extended-spectrum beta-lactamase. The gene expressing the pI 8.8 beta-lactamase was cloned. Nucleotide sequencing revealed a beta-lactamase gene that differs from the gene encoding CTX-M-2, which also originated from S. typhimurium, by 11 nucleotides, 4 of which result in amino acid substitutions: Ala27Thr, Val230Gly, Glu254Ala, and Ile278Val. These results indicated the presence of a novel extended-spectrum beta-lactamase, designated CTX-M-5, that specifically confers resistance to cefotaxime.

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Figures

FIG. 1
FIG. 1
Nucleotide sequence of the blaCTX-M-5 β-lactamase gene. Underlined nucleotides are start and stop codons.
FIG. 2
FIG. 2
Derived amino acid sequence of the CTX-M-5 β-lactamase compared to the cefotaxime-hydrolyzing β-lactamases CTX-M-1, CTX-M-2 (5), CTX-M-3 (13), CTX-M-4 (12), Toho-1 (15), and Toho-2 (18). Dots indicate identical amino acids; underlining indicates the 70SXXK73, 130SDN132, E-166, and 234KTG236 conserved sequences that are typical of class A serine β-lactamases. Amino acid numbering is according to the scheme outlined by Ambler et al. (1).
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