Pérez-Llarena, Francisco J.Zamorano, LauraKerff, FrédéricBeceiro Casas, AlejandroGarcía, PatriciaMiró, ElisendaLarrosa, NievesGómez-Bertomeu, FredericMéndez, José AntonioGonzález-López, Juan JoséOliver, AntonioGalleni, MorenoNavarro, FerránBou, Germán2026-09-042026-09-042014-08-18Pérez-Llarena FJ, Zamorano L, Kerff F, Beceiro A, García P, Miró E, Larrosa N, Gómez-Bertomeu F, Méndez JA, González-López JJ, Oliver A, Galleni M, Navarro F, Bou G. Genetic and kinetic characterization of the novel AmpC β-lactamases DHA-6 and DHA-7. Antimicrob Agents Chemother. 2014 Nov;58(11):6544-9.1098-6596https://hdl.handle.net/2183/49156[Abstract] During a Spanish surveillance study, two natural variants of DHA β-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 β-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 β-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.engAttribution 4.0 Internationalhttp://creativecommons.org/licenses/by/4.0/Anti-Bacterial AgentsBacterial ProteinsEnterobacter cloacaeEscherichia colibeta-Lactamasesjournal articleopen access10.1128/AAC.03144-14