Experimental infection of weanling pigs with Salmonella typhisuis: effect of feeding low concentrations of chlortetracycline, penicillin, and sulfamethazine

Clinical and pathologic variables of Salmonella typhisuis infections were studied in weanling pigs. The influence of daily feeding of low concentrations of chlortetracycline, penicillin, and sulfamethazine on S typhisuis infection also was determined. Ten pigs (group 1) given feed containing low concentrations of chlortetracycline, penicillin, and sulfamethazine when orally inoculated with S typhisuis became pyretic, developed a mild neutrophilia, and had increased serum agglutinating antibody titers, but were clinically normal. Lesions were not present, and S typhisuis was not isolated from 2 group-1 pigs that were killed and necropsied on postinoculation day 8. Then, the antimicrobial agents were withdrawn from the feed of the remaining 8 pigs for 6 days. The pigs were reinoculated with S typhisuis on postinoculation day 16 and developed mild clinical disease with sustained high rectal temperatures. Severe necrotizing typhlocolitis and ulcerative proctitis were found at necropsy in all 8 of the pigs. Similar findings were induced in 7 additional pigs (group 2) that were concurrently inoculated with S typhisuis, but that had no previous exposure to S typhisuis. Successful isolation of S typhisuis required special care and media.