The molecular epidemiology of ampC-mediated resistance in Escherichia coli: A study of clinical strains isolated from the South West region

Lewis, Jonathan

Abstract

Escherichia coli is a common human pathogen, capable of causing a wide range of infections. Some strains produce AmpC beta-lactamase, an enzyme able to affect the action of antibiotics. These strains are often resistant to cephalosporin antibiotics, causing problems for clinical treatment. The production of the enzyme can be mediated by either mutations in the chromosomal ampC promoter region, or through the acquisition of ampC plasmid genes from other species.
In this study, SYBR Green real-time PCR was used to detect blaAmpC and blaCTX-M genes in E. coli strains collected in Gloucester and four other laboratories in the South West region (Dorchester, Swindon, Taunton and Truro). Following a small pilot study, a larger study of 276 strains collected from the five laboratories was undertaken. Strains were tested for the presence of acquired blaAmpC genes and blaCTX-M extended-spectrum beta-lactamase (ESBL) genes. The ampC promoter region for each strain was sequenced, and all strains were typed using multi-locus sequence typing (MLST).
AmpC plasmids were identified in 19 strains (15 with CIT-type and 4 with DHA-type). The most common ampC promoter mutation was a T to A transition at position -32, seen in a total of 36 strains. This was in contrast to other studies, in which the most common mutation is found at position -42. MLST confirmed the expected dominance of the ST131 clone (43.6% of strains) within the cefpodoxime-resistant strains in the South West. There was no evidence for a dominant clone within the AmpC plasmid strains, but some potential evidence for a dominant clone of ST12 with the -32 ampC mutation present.
Overall, in 276 E. coli strains with cefpodoxime-resistance, 25.8% were confirmed as having a genotype associated with AmpC resistance. The remaining strains were largely carrying a blaCTX-M gene (57.1%) or another type of ESBL (16.4%).

Citation

Lewis, J. (in press). The molecular epidemiology of ampC-mediated resistance in Escherichia coli: A study of clinical strains isolated from the South West region. (Thesis). University of the West of England. Retrieved from https://uwe-repository.worktribe.com/output/915314

• Thesis Type: Thesis
• Acceptance Date: Jan 11, 2016
• Publicly Available Date: Jun 7, 2019
• Keywords: molecular epidemiology, ampC, resistance, Escherichia coli
• Public URL: https://uwe-repository.worktribe.com/output/915314
• Award Date: Jan 11, 2016