title: An investigation of horizontal transfer of feed introduced DNA to the aerobic microbiota of the gastrointestinal tract of rats.
abstract: BACKGROUND
  Horizontal gene transfer through natural transformation of members of the microbiota of the lower gastrointestinal tract (GIT) of mammals has not yet been described. Insufficient DNA sequence similarity for homologous recombination to occur has been identified as the major barrier to interspecies transfer of chromosomal DNA in bacteria. In this study we determined if regions of high DNA similarity between the genomes of the indigenous bacteria in the GIT of rats and feed introduced DNA could lead to homologous recombination and acquisition of antibiotic resistance genes.
  
  
  RESULTS
  Plasmid DNA with two resistance genes (nptI and aadA) and regions of high DNA similarity to 16S rRNA and 23S rRNA genes present in a broad range of bacterial species present in the GIT, were constructed and added to standard rat feed. Six rats, with a normal microbiota, were fed DNA containing pellets daily over four days before sampling of the microbiota from the different GI compartments (stomach, small intestine, cecum and colon). In addition, two rats were included as negative controls. Antibiotic resistant colonies growing on selective media were screened for recombination with feed introduced DNA by PCR targeting unique sites in the putatively recombined regions. No transformants were identified among 441 tested isolates.
  
  
  CONCLUSIONS
  The analyses showed that extensive ingestion of DNA (100 μg plasmid) per day did not lead to increased proportions of kanamycin resistant bacteria, nor did it produce detectable transformants among the aerobic microbiota examined for 6 rats (detection limit < 1 transformant per 1,1 × 10(8) cultured bacteria). The key methodological challenges to HGT detection in animal feedings trials are identified and discussed. This study is consistent with other studies suggesting natural transformation is not detectable in the GIT of mammals.
authors.affiliation: GenØk, Centre for Biosafety, Science Park, 9294 Tromsø, Norway.
authors.forename: Lise
authors.initials: L
authors.lastname: Nordgård
authors.forename: Lorenzo
authors.initials: L
authors.lastname: Brusetti
authors.forename: Noura
authors.initials: N
authors.lastname: Raddadi
authors.forename: Terje
authors.initials: T
authors.lastname: Traavik
authors.forename: Beate
authors.initials: B
authors.lastname: Averhoff
authors.forename: Kaare Magne
authors.initials: KM
authors.lastname: Nielsen
mesh_terms: D000150:Acinetobacter / Q000187:drug effects / Q000235:genetics / Q000254:growth & development; D000332:Aerobiosis; D000821:Animal Feed / Q000032:analysis*; D000818:Animals; D000900:Anti-Bacterial Agents / Q000494:pharmacology; D001419:Bacteria / Q000187:drug effects / Q000235:genetics / Q000254:growth & development; D058491:Bacterial Load; D004247:DNA / Q000032:analysis* / Q000235:genetics; D004269:DNA, Bacterial / Q000032:analysis / Q000235:genetics; D024881:Drug Resistance, Bacterial / Q000235:genetics; D005260:Female; D041981:Gastrointestinal Tract / Q000382:microbiology*; D022761:Gene Transfer, Horizontal; D008297:Male; D054892:Metagenome / Q000235:genetics*; D010957:Plasmids / Q000235:genetics; D016133:Polymerase Chain Reaction; D012336:RNA, Ribosomal, 16S / Q000235:genetics; D012338:RNA, Ribosomal, 23S / Q000235:genetics; D051381:Rats; D017208:Rats, Wistar
chemical_list: D000900:Anti-Bacterial Agents; D004269:DNA, Bacterial; D012336:RNA, Ribosomal, 16S; D012338:RNA, Ribosomal, 23S; D004247:DNA