Évaluation de l'acquisition de la résistance à la colistine chez Escherichia coli O149 chez le porc
Post-weaning diarrhea is an important swine disease in Québec mainly caused by Escherichia coli O149. The most frequent treatment used is neomycin, but due to antimicrobial resistance to this antibiotic, veterinarians often use colistin sulfate (CS). CS binds the lipopolysaccharides (LPS) and causes a displacement of divalent cations causing pore formation in the membrane, leading to cellular death. The two component system PmrA/PmrB is the most frequently associated with CS resistance in E. coli by adding à L-Ara4N group to the LPS, increasing its charge, reducing affinity for CS. The main objective of this study was to investigate the genetic polymorphism in pmrA/pmrB genes in E. coli strains acquired in vitro and in an infectious model of post-weaning diarrhea in piglets. For the in vitro assay, we used swine clinical E. coli strains resistant to neomycin isolated from 2008 to 2011. We created 22 mutants resistant to CS. MIC was determined by standard double dilution method and compared to the EUCAST breakpoint. By sequencing the genes pmrA and pmrB, we identified seven new genetic polymorphisms, 3 were in PmrA: A80V, N128I, S144G and 4 in pmrB gene: V87E, D148Y, D148V, T156M. For the in vivo assay, we followed the experimental infection ETEC:F4 E. coli strain and commensal E. coli isolates through a post-weaning infectious model. Sequencing of pmrA and pmrB showed two polymorphisms G15R and T156M, respectively. Many E. coli strains acquired in vitro and in vivo resistance to colistin without mutation in pmrA/pmrB suggesting other(s) mechanism(s) of resistance to this antibiotic.
E. coli Polymyxine E PmrA/PmrB Post weaning diarrhea Swine Colistin Polymyxin E Two components system Antimicrobial resistance Genetic polymorphism