Reference | Van.Der.Horst_2013_FooPatandDis (10293)

The experiments were designed to study the effect of administration of antibiotics in drinking water on the resistance of the E. coli bacteria in the feces of layer chickens. The birds were obtained from the specific pathogen free (SPF) flock of the Animal Health Service (De Gezondheidsdienst voor Dieren [GD]) in Deventer, The Netherlands. The original flock was owned by GD since 2003 and has never been medicated. Each group consisted of 15 males, 11 weeks old, with an average weight of 1.18 kg per bird. Each group of birds was housed in HEPA-filtered isolators with a surface area of 13800 cm^2 each. The slats of the isolators were covered with plastic to ensure direct contact with feces. A lighting program of 8 h of light and 14 h of dark was used. Each group had ad libitum drinking water and ad libitum complete formulated pullet feed. A total of 10 groups of 15 chickens each were used in the study: one control and three experimental groups for each antibiotic. The control group did not receive any antibacterial treatment. For each of the three antibiotics (amoxicillin, oxytetracycline, and enrofloxacin), the following treatments were used: (1) One group was treated with an antibiotic in the therapeutical dose (according to the registration of the product). (2) Another group was treated with reduced therapeutical dose (75% of the therapeutical dose). (3) A third group was treated with a carry-over dose (2.5% of the therapeutical dosage). Therapeutical dosages for the antibiotics used were as follows: amoxicillin (Paracilline) 20 mg/kg body weight, oxytetracycline (Oxytetracycline HCl) 20 mg/kg body weight, and enrofloxacin (Baytril) 8 mg/kg body weight (Table 1). Medication was given for a period of 48 h. The antibiotics were dissolved in the drinking water based on the dosage per kg body weight of the active compound of the antibiotic. The following antibiotics were used: (1) Amoxicillin (Paracilline; Intervet REG NL 4256): 1 g of Paracilline is 697 mg of amoxicillin. (2) Oxytetracycline (Oxytetracycline HCl; Eurovet Reg NL 8678): 1 g of Oxytetracycline HCl is 1 g of oxytetracycline. (3) Enrofloxacin (Baytril 10% oral solution; Bayer REG NL 2929): 1 mL of Baytril is 100 mg of enrofloxacin. The drinking water medication was prepared daily and calculated on the basis of the daily average body weight and the average water consumption of all the groups. The treated groups were given the fixed amount of medicated water, which was the average water intake of all the groups of the 2 days prior to the treatments. At 24 h after the administration of the water, the remaining water was weighed, the average water intake calculated, and the antibiotic intake determined.

All birds were sampled using cloacal swabs 1 day prior to the start of the treatment, daily during the treatment period, and five times in a period of 15 days after ending the treatment. Swabs were used to identify E. coli strains that were resistant towards the antibiotic that was applied.

AST Method: Unclear

Reference explicitly reports AST breakpoints: True

Reference reports using a MIC table: False