Usefulness of a Vancomycin pretreatment when challenging chickens in order to evaluate anti-Salmonella preparations

For many years, Salmonella infection models have been developed in chickens with the aim to study the effects of prophylactic or therapeutic measures on the colonization of the gut. However, although the literature includes numerous challenge models, few studies investigated the infection rates among the inoculated population. We have implemented an antibiotic pretreatment of the chickens (vancomycin hydrochloride, 25 mg/bird) as an infection promoter. Indeed, vancomycin affects the normal gut microflora and releases sites for Salmonella at the intestinal epithelium. Two experiments were undertaken and a presence/absence cloacal swab method was used to evaluate cecal colonization. In the first experiment, birds were orally inoculated with Salmonella Typhimurium at 21 days of age. Three inoculum doses (3 × 103, 3 × 106, 3 × 109 cfu/bird) and an uninfected control were compared according to whether or not vancomycin had been used. Higher levels of Salmonella colonization (more than 70 %) were achieved in the gut by pretreating birds with vancomycin before inoculation (P < 0.05). In the second experiment, chicks were inoculated at 7 days of age with 108 cfu/bird after a vancomycin pretreatment, leading to an infection rate of 87.5 %. In conclusion, vancomycin promotes efficiently the percentage of colonized birds in the challenged population, with either young animals or olders.