Molecular characterisation of acquired and overproduced chromosomal blaAmpC in Escherichia coli clinical isolates

Int J Antimicrob Agents. 2016 Jan;47(1):62-8. doi: 10.1016/j.ijantimicag.2015.10.007. Epub 2015 Nov 2.

Abstract

Escherichia coli recovered from three hospitals in Barcelona (Spain) were studied to determine the prevalence of isolates with acquired AmpC (ac-AmpC) and/or overproduced chromosomal AmpC (c-AmpC). Mechanisms involved in blac-AmpC overexpression, blaac-AmpC and the plasmids associated with their distribution as well as the prevalence of plasmid-mediated quinolone resistance (PMQR) in AmpC-producing isolates were also determined. Isolates were selected according to their resistance phenotype. blaac-AmpC, alterations in the blac-AmpC promoter/attenuator, and PMQR genes [qnrA, qnrB, qnrS, aac(6')-Ib-cr and qepA] were characterised by PCR and sequencing. blac-AmpC expression was determined by qRT-PCR. Population structure analysis was performed using PFGE, MLST and phylogenetic group PCR. Plasmids carrying blaac-AmpC were characterised by PCR-based replicon typing and S1-PFGE. IncI1 and IncF plasmids were also analysed by plasmid MLST and replicon sequence typing, respectively. Among 21563 E. coli isolates, 240 (1.1%) overproduced AmpC β-lactamases, including 180 (75.0%) harbouring ac-AmpC (132 CMY-2 variants and 48 DHA-1) and 60 (25.0%) c-AmpC enzymes. Three mutation profiles in the blac-AmpC promoter/attenuator were associated with a 72.5-, 19.9- and 5.8-fold increased expression, respectively. Moreover, 63.3% of ac-AmpC and 43.3% of c-AmpC isolates belonged to B2, D, E or F phylogenetic groups. PMQR was found in 31% of ac-AmpC isolates [38 qnrB4, 8 aac(6')-Ib-cr, 6 qnrS1 and 3 qnrB19] and in 10% of c-AmpC isolates [5 aac(6')-Ib-cr and 1 qnrS1]. IncI1-ST12 and IncF were associated with blaCMY-2 and blaDHA-1, respectively. These results suggest that ac-AmpC β-lactamases were the main mechanism of AmpC production. Isolates and plasmids both showed high genetic diversity.

Keywords: AmpC promoter; Antimicrobial resistance; Cephalosporins; PMQR; pMLST.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Bacterial Proteins / genetics*
  • Bacterial Proteins / metabolism*
  • Chromosomes, Bacterial
  • DNA Fingerprinting
  • DNA, Bacterial / chemistry
  • DNA, Bacterial / genetics
  • Drug Resistance, Bacterial
  • Electrophoresis, Gel, Pulsed-Field
  • Escherichia coli / classification
  • Escherichia coli / enzymology*
  • Escherichia coli / genetics*
  • Escherichia coli Infections / microbiology*
  • Gene Expression
  • Gene Transfer, Horizontal
  • Genes, Bacterial
  • Genetic Variation
  • Humans
  • Multilocus Sequence Typing
  • Mutation
  • Plasmids
  • Polymerase Chain Reaction
  • Quinolones / metabolism
  • Sequence Analysis, DNA
  • Spain
  • beta-Lactamases / genetics*
  • beta-Lactamases / metabolism*

Substances

  • Bacterial Proteins
  • DNA, Bacterial
  • Quinolones
  • AmpC beta-lactamases
  • beta-Lactamases