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 ( npt I and aad A) 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.

Fire in the Forest: Adverse Effects of Antibiotics on the Healthy Human Gut Microbiome

“…12 Mechanisms such as conjugation, transformation, and transduction can cause the transfer of antibiotic resistance genes and the spread of ARGs in the gut microbiome. 103 In transformation, naked DNA which might have antibiotic resistance genes is taken up by a bacterium. 103 During conjugative transfer, resistance genes could spread after the formation of a mating bridge between two cells.…”

“…103 In transformation, naked DNA which might have antibiotic resistance genes is taken up by a bacterium. 103 During conjugative transfer, resistance genes could spread after the formation of a mating bridge between two cells. In this process, plasmids or conjugative transposons will move from a donor cell to a recipient.…”

“…In transduction, resistance genes that are encoded by bacteriophage can transfer from one cell to another and be integrated into the chromosome of the recipient cell in the process termed lysogeny. 103 Transformation does not contribute significantly to horizontal gene transfer in the mammalian intestinal tract. 104 However, both conjugation and transduction are responsible for the horizontal transfer of ARGs.…”

Scientific Opinion on an application (EFSA-GMO-NL-2009-70) for the placing on the market of genetically modified drought tolerant maize MON 87460 for food and feed uses, import and processing under Regulation (EC) No 1829/2003 from Monsanto

“…72 Additional information April 2012April . 2002EFSA, 2009), but competence development and transformation of bacteria by genomic DNA of plants has not been observed in the lower gastrointestinal tract even with optimised model systems providing a selective advantage (Nordgård et al, 2007;Rizzi et al, 2008;EFSA, 2009;Nordgård et al, 2012). Furthermore, not all species have the same degree of competence.…”

“…Some studies have shown that introduced bacteria can be transformed naturally in the oral cavity of humans and animals (see Andersen et al, 2001;Hay et al, 71 The indicated uses of kanamycin or neomycin or similar substances include: gut irrigation; the treatment of encephalopathy in humans (neomycin); treatment of diarrhoea in farm animals; and aerosol administration for respiratory infections in humans and animals (EFSA, 2009 (Nordgård et al, 2007;Rizzi et al, 2008;EFSA, 2009;Nordgård et al, 2012). Furthermore, not all species have the same degree of competence.…”