title: Antimicrobial resistances do not affect colonization parameters of intestinal E. coli in a small piglet group.
abstract: BACKGROUND
  Although antimicrobial resistance and persistence of resistant bacteria in humans and animals are major health concerns worldwide, the impact of antimicrobial resistance on bacterial intestinal colonization in healthy domestic animals has only been rarely studied. We carried out a retrospective analysis of the antimicrobial susceptibility status and the presence of resistance genes in intestinal commensal E. coli clones from clinically healthy pigs from one production unit with particular focus on effects of pheno- and/or genotypic resistance on different nominal and numerical intestinal colonization parameters. In addition, we compared the occurrence of antimicrobial resistance phenotypes and genotypes with the occurrence of virulence associated genes typical for extraintestinal pathogenic E. coli.
  
  
  RESULTS
  In general, up to 72.1% of all E. coli clones were resistant to ampicillin, chloramphenicol, kanamycin, streptomycin, sulfamethoxazole or tetracycline with a variety of different resistance genes involved. There was no significant correlation between one of the nominal or numerical colonization parameters and the absence or presence of antimicrobial resistance properties or resistance genes. However, there were several statistically significant associations between the occurrence of single resistance genes and single virulence associated genes.
  
  
  CONCLUSIONS
  The demonstrated resistance to the tested antibiotics might not play a dominant role for an intestinal colonization success in pigs in the absence of antimicrobial drugs, or cross-selection of other colonization factors e.g. virulence associated genes might compensate "the cost of antibiotic resistance". Nevertheless, resistant strains are not outcompeted by susceptible bacteria in the porcine intestine.
authors.affiliation: Institut für Mikrobiologie und Tierseuchen, Freie Universität Berlin, Philippstr 13, 10115 Berlin, Germany. Peter.Schierack@HS-Lausitz.de
authors.forename: Peter
authors.initials: P
authors.lastname: Schierack
authors.forename: Kristina
authors.initials: K
authors.lastname: Kadlec
authors.forename: Sebastian
authors.initials: S
authors.lastname: Guenther
authors.forename: Matthias
authors.initials: M
authors.lastname: Filter
authors.forename: Stefan
authors.initials: S
authors.lastname: Schwarz
authors.forename: Christa
authors.initials: C
authors.lastname: Ewers
authors.forename: Lothar H
authors.initials: LH
authors.lastname: Wieler