Variations of the Escherichia coli population in the digestive tract of broilers.

We explored the between-group and temporal variations in the intestinal Escherichia coli populations of broilers under experimental conditions, taking both antimicrobial resistance and virulence into consideration. Four replicates of 45 commercial chicks were reared in four animal facilities. On their first day of life (Day 0), they were orally inoculated with two extended-spectrum-cephalosporin-resistant (ESCR) E. coli (2.72 log10 CFU of a bla CMY-2- and 2.55 log10 CFU of a bla CTX-M-carrying E. coli). Faecal samples were then collected weekly and caecal samples were obtained from birds sacrificed on Days 21 or 42. The total, ESC-, ciprofloxacin- and gentamicin-resistant E. coli populations were enumerated on MacConkey (MC) and MC-supplemented media, and eight virulence-associated genes (VAGs) (iroN, iutA, iss, ompT, hlyF, vat, frzorf4 , and fyuA) were sought by PCR on isolates obtained on MC agar. The results showed significant between-group differences in the size of the resistant sub-populations and the presence of VAGs. Contrary to bla CTX-M-positive strains, bla CMY-positive strains persisted up to Day 42, but represented only a minor fraction of the total E. coli population. The ESC-, gentamicin- and ciprofloxacin-resistant populations decreased over time. Isolates obtained during the first week contained a mean of 5.1 VAGs. The percentages of some VAG profiles differed between faecal isolates on Day 41 and caecal isolates on Day 42. The fluctuations or differences between E. coli isolates according to group, age, and faecal or caecal origin need to be considered when designing experimental protocols and seeking to improve colibacillosis control. RESEARCH HIGHLIGHTS Temporal variations in the intestinal E. coli populations of broilers was studied. The antibiotic-resistant populations decreased over time. Virulence profiles differed between faecal isolates on Day 41 and caecal isolates on Day 42. Strains with the highest numbers of virulence genes were present during the first days.

Enterohemorrhagic Escherichia coli Hybrid Pathotype O80:H2 as a New Therapeutic Challenge.

We describe the epidemiology, clinical features, and molecular characterization of enterohemorrhagic Escherichia coli (EHEC) infections caused by the singular hybrid pathotype O80:H2, and we examine the influence of antibiotics on Shiga toxin production. In France, during 2005-2014, a total of 54 patients were infected with EHEC O80:H2; 91% had hemolytic uremic syndrome. Two patients had invasive infections, and 2 died. All strains carried stx2 (variants stx2a, 2c, or 2d); the rare intimin gene (eae-ξ); and at least 4 genes characteristic of pS88, a plasmid associated with extraintestinal virulence. Similar strains were found in Spain. All isolates belonged to the same clonal group. At subinhibitory concentrations, azithromycin decreased Shiga toxin production significantly, ciprofloxacin increased it substantially, and ceftriaxone had no major effect. Antibiotic combinations that included azithromycin also were tested. EHEC O80:H2, which can induce hemolytic uremic syndrome complicated by bacteremia, is emerging in France. However, azithromycin might effectively combat these infections.