University of Leicester
2015Horvath-PappEPhD.pdf (3.98 MB)

Analysis of the fitness cost of integrons in clinical isolates of acinetobacter baumannii

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posted on 2015-05-12, 08:54 authored by Eva Horvath-Papp
Antibiotic resistance determinants carried on mobile genetic elements such as integrons are widespread in Acinetobacter baumannii. A total of 76 clinical isolates of A. baumannii were screened for class 1, 2 and 3 integron structures using PCR-based assays. Further chromosome walking and Southern blot-based analyses revealed a significant proportion of incomplete integrons, primarily due to IS element-mediated deletions or truncations at the 5’ end of these integrons. Based on these multiple detection methods, a total of 72 integron structures distributed among 58 isolates were identified. Remarkably, 29 (40.3 %) were either incomplete, or had a truncated integrase gene. These data also revealed that using established PCR-based detection methods alone would yield high rates of false-negative and –positive results. The high frequencies of intI1 and/or 5’ end integron truncations suggest that IntI1 amelioration confers a significant selective advantage. This hypothesis was investigated in E. coli and A. baumannii backgrounds using an IPTG-inducible IntI1-expressing plasmid. Significant fitness costs were observed through growth curve analysis when IntI1 was overexpressed in recA-deficient E. coli lab strains, and also in an A. baumannii strain. The latter was predicted to have a ~1.5-fold higher number of non-canonical IntI1 recombination sites in a typical E. coli strain. The archetypal intI1 repressor, LexA, is not present in the A. baumannii genome, so the role of the closest homologue, ∆UmuDAb, was investigated through knockout studies. ΔumuDAb mutants were created through allelic exchange, and although the mutants showed a significant upregulation of intI1 expression, when the mutants were complemented with a umuDAb-overexpressing plasmid, intI1 expression was also increased, albeit to a lesser extent. This study demonstrates a complex DNA-damage response in A. baumannii, and will aid further investigation for a full understanding of the development and maintenance of antibiotic resistance in this important nosocomial pathogen.



Rajakumar, Kumar

Date of award


Author affiliation

Department of Infection, Immunity and Inflammation

Awarding institution

University of Leicester

Qualification level

  • Doctoral

Qualification name

  • PhD



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