Genetic variability among ampC genes from acinetobacter genomic species 3

Antimicrob Agents Chemother. 2009 Mar;53(3):1177-84. doi: 10.1128/AAC.00485-08. Epub 2008 Nov 24.


As a part of a nationwide study in Spain, 15 clinical isolates of Acinetobacter genomic species 3 (AG3) were analyzed. The main objective of the study was to characterize the ampC genes from these isolates and to determine their involvement in beta-lactam resistance in AG3. The 15 AG3 isolates showed different profiles of resistance to ampicillin (range of MICs, 12 to >256 microg/ml). Nucleotide sequencing of the 15 ampC genes yielded 12 new AmpC enzymes (ADC-12 to ADC-23). The 12 AG3 enzymes showed 93.7 to 96.1% amino acid identity with respect to the AmpC enzyme from Acinetobacter baumannii (ADC-1 enzyme). Eight out of fifteen ampC genes were expressed in Escherichia coli cells under the control of a common promoter, and with the exception of one isolate (isolate 65, which showed lower beta-lactam MICs), significant differences in overall beta-lactam MICs for E. coli cells expressing AG3 ampC genes were not revealed. No significant differences in ampC gene expression in AG3 clinical isolates were revealed by reverse transcription-PCR analysis. A detailed analysis of the 12 AmpC protein sequences revealed that amino acid replacements (in comparison with those of ADC-1) occurred mainly in the same positions, although none were located in important functional domains such as the Omega- loop or conserved beta-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 beta-lactams. No ISAba1 was detected upstream of the ampC genes. Our results reveal 12 new ampC genes in AG3. The enzymes showed a moderate degree of variability, and they are tentatively named ADC-12 to ADC-23.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Acinetobacter / classification
  • Acinetobacter / enzymology
  • Acinetobacter / genetics*
  • Acinetobacter / isolation & purification
  • Acinetobacter / metabolism
  • Acinetobacter baumannii / enzymology
  • Amino Acid Sequence
  • Ampicillin Resistance / genetics
  • Anti-Bacterial Agents / pharmacology
  • Bacterial Proteins / genetics*
  • Bacterial Proteins / metabolism
  • Escherichia coli / genetics
  • Genes, Bacterial*
  • Genetic Variation*
  • Humans
  • Kinetics
  • Microbial Sensitivity Tests
  • Models, Molecular
  • Molecular Sequence Data
  • Promoter Regions, Genetic
  • Reverse Transcriptase Polymerase Chain Reaction
  • Sequence Homology, Amino Acid
  • Spain
  • beta-Lactam Resistance / genetics


  • Anti-Bacterial Agents
  • Bacterial Proteins