Genetic and kinetic characterization of the novel AmpC ß-lactamases DHA-6 and DHA-7.
Antimicrob Agents Chemother
; 58(11): 6544-9, 2014 Nov.
Article
em En
| MEDLINE
| ID: mdl-25136023
ABSTRACT
During a Spanish surveillance study, two natural variants of DHA ß-lactamases, DHA-6 and DHA-7, were found, with the replacements Ala226Thr and Phe322Ser, respectively, with respect to DHA-1. The DHA-6 and DHA-7 enzymes were isolated from Escherichia coli and Enterobacter cloacae clinical isolates, respectively. The aim of this study was to genetically, microbiologically, and biochemically characterize the DHA-6 and DHA-7 ß-lactamases. The blaDHA-6 and blaDHA-7 genes were located in the I1 and HI2 incompatibility group plasmids of 87.3 and 310.4 kb, respectively. The genetic contexts of blaDHA-6 and blaDHA-7 were similar to that already described for the blaDHA-1 gene and included the qnrB4 and aadA genes. The MICs for cephalothin, aztreonam, cefotaxime, and ceftazidime were 8- to 32-fold lower for DHA-6 than for DHA-1 or DHA-7 expressed in the same isogenic E. coli TG1 strain. Interestingly, the MIC for cefoxitin was higher in the DHA-6-expressing transformant than in DHA-1 or DHA-7. Biochemical studies with pure ß-lactamases revealed slightly lower catalytic efficiencies of DHA-6 against cephalothin, ceftazidime, and cefotaxime than those of DHA-1 and DHA-7. To understand this behavior, stability experiments were carried out and showed that the DHA-6 protein displayed significantly higher stability than the DHA-1 and DHA-7 enzymes. The proximity of Thr226 to the N terminus in the tertiary protein structure in DHA-6 may promote this stabilization and, consequently, may induce a slight reduction in the dynamic of this enzyme that primarily affects the hydrolysis of some of the bulkiest antibiotics.
Texto completo:
1
Base de dados:
MEDLINE
Assunto principal:
Proteínas de Bactérias
/
Beta-Lactamases
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Enterobacter cloacae
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Escherichia coli
/
Antibacterianos
Limite:
Humans
Idioma:
En
Revista:
Antimicrob Agents Chemother
Ano de publicação:
2014
Tipo de documento:
Article
País de afiliação:
Espanha