FACTORS AFFECTING THE INCIDENCE AND ANTI-SALMONELLA ACTIVITY OF THE ANAEROBIC CECAL FLORA OF THE YOUNG CHICK

Different types of anaerobic bacteria (32) isolated from chickens were tested for anti-Salmonella activity in vitro. Under the conditions of the test only Bacteroides hypermegas and a Bifidobacterium sp. inhibited the salmonellae and this was attributed to the production of volatile fatty acids (VFA) coupled with a low pH. When these organisms were tested in newly hatched chicks no inhibition of S. typhimurium occurred. Possible explanations for this observation are considered. The pH value and concentration of VFA in the cecal material were determined in chicks from 0-84 days. In vitro tests with S. typhimurium indicated that, while the organism could multiply at the pH and concentration of VFA found during the first few days after hatching, the rapid increase in VFA concentration during the first 21 days would made this increasingly difficult. The significance of the developing cecal flora in relation to VFA production and pH is discussed. Because certain feed additives influence the carriage of salmonellae, the sensitivity of various cecal anaerobes to these compounds was determined in vitro, generally at 1, 10 and 100 .mu.g/ml. The additives tested included flavomycin, furazolidone, nitrovin, tetracycline, tylosin, sulphaquinoxaline, virginiamycin and Zn bacitracin. All the organisms tested were inhibited by 100 .mu.g/ml furazolidone; none were inhibited by 500 .mu.g/ml sulphaquinoxaline. Changes occurring in the VFA concentration, pH value and microflora of the ceca of chicks fed for 49 days or longer on a normal starter diet of the same diet containing 10 or 100 mg/kg nitrovin were compared. When the chicks were fed on the diet containing 100 mg/kg nitrovin, the gram-negative non-sporing anaerobes were eliminated as a significant part of the cecal flora. The VFA concentration combined with a low pH in chicks from 2 wk onward was still sufficient to inhibit Salmonella multiplication. Other possibly interrelated factors which might lead to an increased Salmonella carrier rate in the nitrovin-treated chickens are discussed.