INGESTED FOREIGN (PHAGE M13) DNA SURVIVES TRANSIENTLY IN THE GASTROINTESTINAL-TRACT AND ENTERS THE BLOOD-STREAM OF MICE

Is the epithelial lining of the mammalian gastrointestinal (GI) tract a tight barrier against the uptake of ingested foreign DNA or can such foreign DNA penetrate into the organism? We approached this question by pipette-feeding circular or linearized double-stranded phage M13 DN A to mice or by adding M13 DNA to the food of mice whose fecal excreti ons had previously been shown to be devoid of this DNA. At various pos t-prandial times, the feces of the animals was tested for M13 DNA sequ ences by Southern or dot blot hybridization or by the polymerase chain reaction (PCR). On Southern blot hybridization, the majority of M13 D NA fragments were found in the size range between < 200 and 400 bp (ba se pairs). For the PCR analysis, synthetic oligodeoxyribonucleotide pr imers were spaced on the M13 DNA molecule such that the sizes of the p ersisting M13 DNA fragments could be determined. We also extracted DNA from whole blood or from sedimented blood cells of the animals at dif ferent times after feeding M13 DNA and examined these DNA preparations for the presence of M13 DNA by dot blot hybridization or by PCR. M13 DNA fragments were found between 1 and 7 h postprandially in the feces of mice. By PCR analysis, fragments of 712, 976, and 1692 bp in lengt h were detected. In DNA from blood, M13 DNA fragments of up to 472 bp were found by PCR between 2 and 6 h after feeding. Dot blot or Souther n blot hybridization revealed M13 DNA at 2 and 4 h, but not at 1, 8 or 24 h after feeding. This DNA was shown to be DNase sensitive. M13 DNA was found both in blood cells and in the serum. A segment of about 40 0 bp of the DNA amplified by PCR from feces or blood was analyzed for its nucleotide sequence which was found to be identical to that of aut hentic M13 DNA, except for a few deviations. M13 DNA could not be dete cted in the feces or in the blood of the animals prior to feeding or p rior to 1 h and later than 7 h after feeding. These controls attest to the validity of the results and also argue against the possibility th at the murine GI tract had been colonized by phage M13. Moreover, M13 DNA-positive bacterial colonies were never isolated from the feces of animals that had ingested M13 DNA. The results of reconstitution exper iments suggested that 2 to 4% of the orally administered M13 DNA could be detected in the GI tract of mice. A proportion of about 0.01% to 0 .1% of the M13 DNA fed could be retrieved from the blood.