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

Timothy S. Frana Department of Veterinary Microbiology and Preventive Medicine, College of Veterinary Medicine, Iowa State University, Ames, IA 50010.
Present address is USDA, Animal and Plant Health Inspection Service, the Center for Veterinary Biologics, 510 S 17th St, Ste 104, Ames, IA 50010.

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Steven A. Carlson USDA, Agricultural Research Service, Preharvest Food Safety and Enteric Disease Research Unit, National Animal Disease Center, Ames, IA 50010.

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Daryl C. Rauser Department of Veterinary Microbiology and Preventive Medicine, College of Veterinary Medicine, Iowa State University, Ames, IA 50010.

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Bradley D. Jones Department of Microbiology, College of Medicine, University of Iowa, Iowa City, IA 52242.

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Brian J. Fergen Center for Veterinary Biologics, 510 S 17th St, Ste 104, Ames, IA 50010.

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Ronald W. Griffith Department of Veterinary Microbiology and Preventive Medicine, College of Veterinary Medicine, Iowa State University, Ames, IA 50010.

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Abstract

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 during necropsy.

Results—Differences in shedding of Salmonella Typhimurium were not detected between groups receiving Mcc24-producing or non–Mcc24-producing E coli. No significant differences were found in quantitative analysis between groups receiving Mcc24-producing and non–Mcc24-producing E coli. Evidence of maractivation was not detected.

Conclusions and Clinical Relevance—Microcin-producing E coli did not exert an effect on shedding of Salmonella Typhimurium or maractivation in pigs. It may be difficult or impractical to create the conditions required for Mcc24 to be an effective part of a food safety intervention to reduce shedding of Salmonella Typhimurium. (Am J Vet Res 2004;65:1616–1620)

Abstract

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 during necropsy.

Results—Differences in shedding of Salmonella Typhimurium were not detected between groups receiving Mcc24-producing or non–Mcc24-producing E coli. No significant differences were found in quantitative analysis between groups receiving Mcc24-producing and non–Mcc24-producing E coli. Evidence of maractivation was not detected.

Conclusions and Clinical Relevance—Microcin-producing E coli did not exert an effect on shedding of Salmonella Typhimurium or maractivation in pigs. It may be difficult or impractical to create the conditions required for Mcc24 to be an effective part of a food safety intervention to reduce shedding of Salmonella Typhimurium. (Am J Vet Res 2004;65:1616–1620)

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