Effects of different levels of chlortetracycline in the diet of turkey poults artifically-infected with Salmonella typhimurium.

Two separate experiments were conducted to assess the shed rate and duration of shed of S . typhimurium organisms from turkey poults orally infected with chlortetracycline-sensitive S. typhimurium in relation to chloretetracycline (CTC) given in the feed at 0, growth promotant, subtherapeutic and therapeutic levels; the emergence of resistant S. typhimurium organisms in reference to the diet given; in vitro transfer of drug resistance from thses resistant S. typhimurium donor cultures to multiply-sensitive E. coli recipients; and phage type changes, is any, of these S. typhimurium isolates. The results showed that increasing CTC in the diet from 0 to the three levels of antibiotic supplementation, appeared to (a) reduce shed and duration of shed corresponding to each level used; (b) cause a minimal development of drug resistance and its transfer (usually at sub-therapeutic levels of CTC supplementation) for the duration of the experiment; and (c) induce phage type changes in some of the S. typhimurium isolates. These phage type changes question the validity of using phage typing as a tool in epidemiological investigations.