To test the hypothesis that Helicobacter pylori may be transmitted by the o
ral-oral route, we applied nested PCR and DNA sequencing to detect and anal
yze H. pylori DNA in the oral cavity of 20 adult patients undergoing endosc
opy. Dental plaques of molars, premolars, and incisors and saliva were coll
ected. Additional paraffin-embedded gastric biopsies were analyzed in four
patients. Two sets of highly sensitive and specific primers, EHC-U/EHC-L an
d ET5-U/ET-5L directed to a 860-bp fragment of H. pylori DNA, were used in
the nested PCR. Eight patients had an active infection in the stomach deter
mined with the [C-13]urea breath test and the other 12 were negative. Neste
d PCR showed that all 20 subjects (100%) were positive for H. pylori in the
oral cavity. DNA sequencing demonstrated that all tested PCR products of t
he expected size from the oral samples have more than 97% identity with tha
t from H. pylori type strain ATCC 43629, However, sequences differed in ora
l samples from different subjects as well as between different oral locatio
ns and gastric biopsies within the same individuals. In conclusion, the ora
l cavity may be a permanent reservoir for H. pylori and can harbor multiple
H. pylori strains at the same time.