title: Prevalence and patterns of antimicrobial resistance in Campylobacter spp isolated from pigs reared under antimicrobial-free and conventional production methods in eight states in the Midwestern United States.
abstract: OBJECTIVE
  To compare apparent prevalence and patterns of antimicrobial resistance in Campylobacter spp in feces collected from pigs reared with antimicrobial-free versus conventional production methods in 8 states in the Midwestern United States.
  
  
  METHODS
  Cross-sectional study.
  
  
  METHODS
  95 swine farms that used antimicrobial-free (n = 35) or conventional (60) production methods.
  
  
  METHODS
  Fecal samples from 15 pigs/farm were collected. Biochemical and multiplex-PCR analyses were used to identify Campylobacter spp. The minimal inhibitory concentrations of erythromycin, azithromycin, ciprofloxacin, nalidixic acid, gentamicin, and tetracycline for these organisms were determined by use of a commercially available antimicrobial gradient strip. The data were analyzed by use of population-averaged statistical models.
  
  
  RESULTS
  Campylobacter spp were isolated from 512 of 1,422 pigs. A subset (n = 464) of the 512 isolates was available for antimicrobial susceptibility testing. The apparent prevalence of Campylobacter spp isolates from pigs on conventional farms (35.8%) and antimicrobial-free farms (36.4%) did not differ significantly. Resistances to azithromycin, erythromycin, and tetracycline were significantly higher on conventional farms (70.0%, 68.3%, and 74.5%, respectively) than antimicrobial-free farms (20.1%, 21.3%, and 48.8%, respectively). Resistances to azithromycin, erythromycin, and tetracycline declined as the number of years that a farm was antimicrobial-free increased.
  
  
  CONCLUSIONS
  Production method did not affect the apparent prevalence of Campylobacter spp on swine farms. However, antimicrobial-free farms had a significantly lower prevalence of antimicrobial resistance. Although cessation of antimicrobial drug use will lower resistance over time, investigation of other interventions designed to reduce resistance levels is warranted.
authors.affiliation: Department of Veterinary Integrative Biosciences, College of Veterinary Medicine and Biomedical Sciences, Texas A&M University, College Station, TX 77843, USA.
authors.forename: Susan N
authors.initials: SN
authors.lastname: Rollo
authors.forename: Bo
authors.initials: B
authors.lastname: Norby
authors.forename: Paul C
authors.initials: PC
authors.lastname: Bartlett
authors.forename: H Morgan
authors.initials: HM
authors.lastname: Scott
authors.forename: David L
authors.initials: DL
authors.lastname: Wilson
authors.forename: Virginia R
authors.initials: VR
authors.lastname: Fajt
authors.forename: John E
authors.initials: JE
authors.lastname: Linz
authors.forename: Christine E
authors.initials: CE
authors.lastname: Bunner
authors.forename: John B
authors.initials: JB
authors.lastname: Kaneene
authors.forename: John C
authors.initials: JC
authors.lastname: Huber
mesh_terms: D000818:Animals; D000900:Anti-Bacterial Agents / Q000008:administration & dosage* / Q000494:pharmacology; D002167:Campylobacter / Q000187:drug effects*; D002169:Campylobacter Infections / Q000453:epidemiology / Q000382:microbiology / Q000662:veterinary*; D024881:Drug Resistance, Bacterial; D008826:Microbial Sensitivity Tests; D015146:Midwestern United States / Q000453:epidemiology; D015995:Prevalence; D013552:Swine; D013553:Swine Diseases / Q000453:epidemiology / Q000382:microbiology*
chemical_list: D000900:Anti-Bacterial Agents