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Antimicrob. Agents Chemother. doi:10.1128/AAC.00485-08
Copyright (c) 2008, American Society for Microbiology and/or the Listed Authors/Institutions. All Rights Reserved.

Genetic variability among ampC genes from Acinetobacter genomic species 3

Servicio de Microbiología-Unidad de Investigación, Complejo Hospitalario Universitario Juan Canalejo, 15006 La Coruña; Servicios de Microbiología y de Enfermedades Infecciosas, Hospital Virgen Macarena, 41071 Sevilla; Servicio de Microbiología. Hospital Universitario Marqués de Valdecilla, Santander; Servei de Microbiología, Hospital Clinic, 08036 Barcelona; and Servicio de Enfermedades Infecciosas, Hospital Universitario Virgen del Rocío, 41013 Sevilla, Spain

^* To whom correspondence should be addressed. Email: germanbou{at}canalejo.org.

	Abstract

As a part of a nationwide study in Spain, 15 clinical isolates of Acinetobacter genomic species 3 (AG3) were analysed. The main objective of the study was to characterize the ampC genes from these isolates and to determine their involvement in -lactam resistance in Acinetobacter G3. The 15 AG3 isolates showed different profiles of resistance to ampicillin (range of MICs 12 to >256 µg/mL). Nucleotide sequencing of the 15 ampC genes yielded 13 new AmpC enzymes (ADC-12 to ADC-24). The 13 AG3 enzymes showed 93.7-96.1% amino-acid identity with respect to the AmpC enzyme from A. baumannii (ADC-1 enzyme). Eight out of 15 ampC genes were expressed in E. coli under the control of a common promoter and with the exception of one isolate (#65, which showed lower -lactam MIC values), significant differences were not revealed in overall -lactam MICs for E. coli expressing AG3 ampC genes. No significant differences in ampC gene expression in AG3 clinical isolates were revealed by RT-PCR and analysis. A detailed analysis of the 13 AmpC protein sequences revealed that amino acid replacements (in comparison with those of ADC-1) mainly occurred in the same positions, although none were located in important functional domains such as the omega loop or conserved -lactamase motifs. Kinetic experiments performed with three representative AmpC enzymes (ADC-14, -16 and -18) in some cases revealed dramatic changes in K_m and k_cat values for -lactams. No ISAba1 was detected upstream of the ampC genes. Our results reveal 13 new ampC genes in AG3. The enzymes showed a moderate degree of variability and they are tentatively named as ADC-12 to ADC-24