title: Effects of subtherapeutic concentrations of antimicrobials on gene acquisition events in Yersinia, Proteus, Shigella, and Salmonella recipient organisms in isolated ligated intestinal loops of swine.
abstract: OBJECTIVE
  To assess antimicrobial resistance and transfer of virulence genes facilitated by subtherapeutic concentrations of antimicrobials in swine intestines.
  
  
  METHODS
  20 anesthetized pigs experimentally inoculated with donor and recipient bacteria.
  
  
  METHODS
  4 recipient pathogenic bacteria (Salmonella enterica serotype Typhimurium, Yersinia enterocolitica, Shigella flexneri, or Proteus mirabilis) were incubated with donor bacteria in the presence of subinhibitory concentrations of 1 of 16 antimicrobials in isolated ligated intestinal loops in swine. Donor Escherichia coli contained transferrable antimicrobial resistance or virulence genes. After coincubations, intestinal contents were removed and assessed for pathogens that acquired new antimicrobial resistance or virulence genes following exposure to the subtherapeutic concentrations of antimicrobials.
  
  
  RESULTS
  3 antimicrobials (apramycin, lincomycin, and neomycin) enhanced transfer of an antimicrobial resistance plasmid from commensal E coli organisms to Yersinia and Proteus organisms, whereas 7 antimicrobials (florfenicol, hygromycin, penicillin G, roxarsone, sulfamethazine, tetracycline, and tylosin) exacerbated transfer of an integron (Salmonella genomic island 1) from Salmonella organisms to Yersinia organisms. Sulfamethazine induced the transfer of Salmonella pathogenicity island 1 from pathogenic to nonpathogenic Salmonella organisms. Six antimicrobials (bacitracin, carbadox, erythromycin, sulfathiazole, tiamulin, and virginiamycin) did not mediate any transfer events. Sulfamethazine was the only antimicrobial implicated in 2 types of transfer events.
  
  
  CONCLUSIONS
  10 of 16 antimicrobials at subinhibitory or subtherapeutic concentrations augmented specific antimicrobial resistance or transfer of virulence genes into pathogenic bacteria in isolated intestinal loops in swine. Use of subtherapeutic antimicrobials in animal feed may be associated with unwanted collateral effects.
authors.affiliation: Department of Biomedical Sciences, College of Veterinary Medicine, Iowa State University, Ames, IA 50011, USA.
authors.forename: Matt T
authors.initials: MT
authors.lastname: Brewer
authors.forename: Nalee
authors.initials: N
authors.lastname: Xiong
authors.forename: Kristi L
authors.initials: KL
authors.lastname: Anderson
authors.forename: Steve A
authors.initials: SA
authors.lastname: Carlson
mesh_terms: D000818:Animals; D000900:Anti-Bacterial Agents / Q000494:pharmacology*; D001426:Bacterial Proteins / Q000235:genetics / Q000378:metabolism; D024901:Drug Resistance, Multiple, Bacterial / Q000235:genetics*; D004755:Enterobacteriaceae / Q000187:drug effects* / Q000235:genetics* / Q000472:pathogenicity; D015964:Gene Expression Regulation, Bacterial / Q000187:drug effects / Q000502:physiology; D007422:Intestines / Q000382:microbiology*; D011511:Proteus / Q000187:drug effects / Q000235:genetics / Q000472:pathogenicity; D012475:Salmonella / Q000187:drug effects / Q000235:genetics / Q000472:pathogenicity; D012760:Shigella / Q000187:drug effects / Q000235:genetics / Q000472:pathogenicity; D013552:Swine; D014774:Virulence; D015007:Yersinia / Q000187:drug effects / Q000235:genetics / Q000472:pathogenicity
chemical_list: D000900:Anti-Bacterial Agents; D001426:Bacterial Proteins; C419942:Spi1 protein, Salmonella