Effects of microcin 24-producing Escherichia coli on shedding and multiple-antimicrobial resistance of Salmonella enterica serotype Typhimurium in pigs

Objective—To investigate the effect of an Escherichia coli that produced microcin 24 (Mcc24) on shedding of Salmonella enterica serotype Typhimurium in swine and evaluate evidence of in vivo activation of the Mcc24-mediated, multiple-antibiotic resistance ( mar) operon. Animals—36 crossbred weaned pigs. Procedure—24 pigs were allocated to 2 groups (12 pigs/group). Pigs in 1 group received daily oral administration of an Mcc24-producing E coli, whereas the other group received a non–Mcc24-producing E coli. All pigs were challenge exposed with Salmonella Typhimurium χ4232. A third group of 6 pigs received Mcc24-producing E coli and was challenge exposed with an Mcc24-sensitive, marA-deleted strain of SalmonellaTyphimurium 4232. After challenge exposure, fecal samples from all pigs were cultured to detect shedding of Salmonella Typhimurium and Salmonella Typhimurium isolates were screened for resistance to ciprofloxacin. Fecal samples were collected throughout the study, and tissue samples were collected dur...