Journal Article

AmpC cephalosporinase hyperproduction in <i>Acinetobacter baumannii</i> clinical strains

Stéphane Corvec, Nathalie Caroff, Eric Espaze, Cécile Giraudeau, Henri Drugeon and Alain Reynaud

in Journal of Antimicrobial Chemotherapy

Published on behalf of British Society for Antimicrobial Chemotherapy

Volume 52, issue 4, pages 629-635
Published in print October 2003 | ISSN: 0305-7453
Published online October 2003 | e-ISSN: 1460-2091 | DOI:
AmpC cephalosporinase hyperproduction in Acinetobacter baumannii clinical strains

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  • Medical Oncology
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Objective: To compare the genetic environments of ampC genes in different Acinetobacter baumannii isolates showing different levels of β-lactam resistance.

Methods: The patterns of β-lactam resistance and β-lactamase production were investigated for 42 A. baumannii clinical strains. The MICs of various β-lactams were determined in the presence or absence of the class C cephalosporinase inhibitor, cloxacillin (500 mg/L). The ampC gene and its 5′ adjacent sequence were analysed by PCR and DNA sequencing. An RT–PCR method was developed to evaluate ampC transcript levels.

Results: Strains fell into three resistance groups: first, strains with a ceftazidime MIC ≤ 8 mg/L (20 strains, 47.6%); secondly, strains with a ceftazidime MIC 32 mg/L, which was reduced four-fold in the presence of cloxacillin (eight strains, 19%); and thirdly, strains with a ceftazidime MIC ≥ 256 mg/L, which did not decrease in the presence of cloxacillin (14 strains, 33.4%). In all of the resistant isolates (groups II and III), but not in any of the ceftazidime-susceptible isolates (group I), a 1180 bp insert showing all the characteristics of an insertion sequence was detected upstream from the ampC gene. Isolates having this insert overexpress ampC, according to RT–PCR experiments.

Conclusion: Presence of an insertion sequence upstream of ampC in A. baumannii clinical isolates, possibly including a strong promoter, has the potential to cause over-expression of AmpC, resulting in high-level ceftazidime resistance.

Keywords: Keywords: AmpC hyperproducers, insertion sequences, Acinetobacter baumannii

Journal Article.  4801 words.  Illustrated.

Subjects: Medical Oncology ; Critical Care

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