Open Access Research article

An investigation of horizontal transfer of feed introduced DNA to the aerobic microbiota of the gastrointestinal tract of rats

Lise Nordgård12, Lorenzo Brusetti3, Noura Raddadi46, Terje Traavik12, Beate Averhoff5 and Kaare Magne Nielsen12*

Author Affiliations

1 GenØk, Centre for Biosafety, Science Park, 9294 Tromsø, Norway

2 Department of Pharmacy, Faculty of Medicine, University of Tromsø, N-9037 Tromsø, Norway

3 Faculty of Science & Technology, Free University of Bozen/Bolzano, 39100 Bozen/Bolzano, Italy

4 Department of Food Science, Technology and Microbiology, University of Milan, 20133 Milan, Italy

5 Molecular Microbiology & Bioenergetics, Institute of Molecular Biosciences, Goethe University, 60438 Frankfurt/Main, Germany

6 Department of Civil, Environmental and Materials Engineering (DICAM), Faculty of Engineering, University of Bologna, Bologna 40131, Italy

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BMC Research Notes 2012, 5:170  doi:10.1186/1756-0500-5-170

Published: 1 April 2012

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 × 108 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.