Reference | Dheilly2012 (10156)

Two fecal multidrug-resistant E. coli strains and one avian-pathogenic E. coli (APEC) strain were used for the inoculation of birds. The APEC strain was an O78:K80 E. coli isolate susceptible to tetracycline, trimethoprim-sulfadimethoxazole, amoxicillin, and enrofloxacin. 360 specific-pathogen-free (SPF) chicks were randomly allocated to six groups that were placed in six pressure-controlled animal rooms, with filtered air and controlled temperature. The different groups of birds were designated NINT (non-APEC infected, nontreated), APEC-NT (APEC infected, nontreated), APEC-AMX (APEC infected, amoxicillin treated), APEC-SXT (APEC infected, trimethoprim-sulfadimethoxine treated), APEC-OTC (APEC infected, oxytetracycline treated), and APEC-ENR (APEC infected, enrofloxacin treated). At the ages of 14, 15, and 16 days, the birds from the six groups were orally administered a daily 0.1-ml dose of cultures of E. coli 177pMG252 and E. coli 43pMG298. At the age of 17 days, all birds were vaccinated with an infectious bronchitis vaccine in order to increase the clinical signs of colibacillosis. On day 20, birds from five groups (APEC-NT, APEC-AMX, APEC-OTC, APEC-SXT, and APEC-ENR) were inoculated in the left air sac with 0.1 ml of a culture of the APEC O78:K80 strain, and one group, NINT, was left unchallenged. Medication was initiated 1 day later (day 21). Birds from the APEC-OTC, APEC-SXT, APEC-AMX and APEC-ENR groups were treated, respectively, with therapeutic doses of 20 mg/kg of body weight of oxytetracycline, 28 and 6 mg/kg of sulfadimethoxine-trimethoprim, 10 mg/kg of amoxicillin, or 10 mg/kg of enrofloxacin, as recommended by the suppliers. Treatment doses were calculated daily according to body weight and the group’s water consumption. The antibiotics were given in the drinking water. Oxytetracycline was given on three consecutive days, whereas the other medications were administered for 5 days, as indicated in the summary of product characteristics. The actual mean drug consumption calculated for each day according to body weight and water consumption for that day was 22.5 mg/kg for oxytetracycline, 33.4 and 7.15 mg/kg for sulfadimethoxine-trimethoprim, 9.95 mg/kg for amoxicillin, and 9.05 mg/kg for enrofloxacin

Fecal samples were collected from 10 birds in each group either before treatment (days 18 and 21), during treatment (days 21 and 24), or after treatment (days 35, 42, 49, and 63). For each group and each day, the 10 samples were pooled into five pools of 2 fecal samples. (After treatment, 4 days*5 pools = 20 pooled samples total)

AST Method: Disk Diffusion

Reference explicitly reports AST breakpoints: True

Reference reports using a MIC table: True