title: Salmonella antibiotic-mutant strains reduce fecal shedding and organ invasion in broiler chicks.
abstract: We investigated the exposure to antibiotics in the production of antibiotic-mutant strains of Salmonella. Ten isolates of poultry origin were assayed for antibiotic susceptibilities. One strain of Salmonella Enteritidis, one of Salmonella Heidelberg, and one of Salmonella Typhimurium were selected to induce antimicrobial resistance. Each strain was exposed to high concentrations of streptomycin, rifampicin, and nalidixic acid, respectively. Parent and antibiotic-mutant strains were assayed for antibiotic susceptibilities using a commercial microdilution test and the disk susceptibility test. The strains were assessed for virulence genes and evaluated for fecal shedding, cecal colonization, organ invasion, and mean Salmonella counts after inoculation in 1-day-old chicks. The study revealed that exposure to high concentrations of streptomycin produced the antibiotic-mutant strain SE/LABOR/USP/08 and the exposure to rifampicin produced the antibiotic-mutant SH/LABOR/USP/08. These strains showed significantly reduced fecal shedding (P≤0.05) and organ invasion, persisting less than the parental strains and showing no clinical signs in inoculated chicks. High concentrations of nalidixic acid produced the antibiotic-mutant strain ST/LABOR/USP/08, which did not show any differences compared with the parent strain. Likewise, SE/LABOR/USP/08 did not show the expression of plasmid-encoded fimbriae (pefA) and plasmid virulence protein (spvC), suggesting that after exposure to streptomycin, the parent isolate lost the original gene expression, reducing fecal shedding and organ invasion in inoculated chicks.
authors.affiliation: Department of Pathology, College of Veterinary Medicine, University of São Paulo, Av. Prof. Orlando Marques de Paiva 87, CEP 05508-270, Cidade Universitária, Brazil.
authors.forename: L
authors.initials: L
authors.lastname: Revolledo
authors.forename: A J P
authors.initials: AJ
authors.lastname: Ferreira
mesh_terms: D000818:Animals; D000900:Anti-Bacterial Agents / Q000494:pharmacology*; D002645:Chickens; D024901:Drug Resistance, Multiple, Bacterial; D005243:Feces / Q000382:microbiology*; D015964:Gene Expression Regulation, Bacterial; D009154:Mutation; D016133:Polymerase Chain Reaction; D011201:Poultry Diseases / Q000382:microbiology*; D012475:Salmonella / Q000187:drug effects* / Q000235:genetics; D012481:Salmonella Infections, Animal / Q000382:microbiology* / Q000473:pathology; D022562:Salmonella Vaccines; D013047:Specific Pathogen-Free Organisms; D014774:Virulence; D037521:Virulence Factors / Q000235:genetics / Q000378:metabolism
chemical_list: D000900:Anti-Bacterial Agents; D022562:Salmonella Vaccines; D037521:Virulence Factors