Competitive exclusion of salmonellas from the chick caecum using a defined mixture of bacterial isolates from the caecal microflora of an adult bird

Abstract

Colonization of the caeca of newly hatched chicks by Salmonella typhimurium was prevented by oral administration of a mixture of cultures comprising 48 different bacterial strains originating from an adult bird known to be free from salmonellas. The treatment conferred protection to the same degree as that obtained previously with a suspension of adult caecal contents or an undefined anaerobic culture from the same source and was demonstrated in four separate laboratory trials. Examination of the caecal microflora of chicks one day after being given the protective treatment showed that the presence of high levels of lactobacilli and Bacteroides spp. which are not found usually at two days of age in chicks produced under commercial conditions was indicative of the successful establishment of an adult-type microflora. Although the usual method of administering the protective organisms was to dose the chicks directly into the crop, it was also found possible to incorporate the organisms in the drinking water given to the birds at dilutions up to one in five, the maximum tested. When chicks were given the bacterial mixture via the crop and fed on a diet containing 10 mg kg-1 nitrovin and 100 mg kg-1 monensin, the bacteroides failed to establish in the caeca and the birds were not protected against salmonella colonization. However, when the bacterial cultures were incorporated in the drinking water and the chicks given the same feed, normal protection was obtained; possible reasons for these observations are discussed.