Detection of Helicobacter pylori DNA in feces and saliva by polymerase chain reaction: a review

The polymerase chain reaction (PCR), known for its high sensitivity and specificity, has been used for the detection of Helicobacter pylori DNA in bodily materials such as feces and saliva. Since fecal specimens contain PCR inhibitors, DNA before PCR amplification has been purified using various biochemical, immunological and physical pre-PCR steps. Several PCR protocols, differing from each other in the selection of genomic targets and primers, have produced varying degrees of specificity and sensitivity in detecting H. pylori DNA. PCR identified antimicrobial resistance of H. pylori in feces. It also detected virulence factor genes such as the cytotoxin-associated gene (cagA) and vacuolating cytotoxin gene (vacA) in feces and saliva. While the cagA gene was detected in 50-60% of fecal specimens, it was found in 25% of salivary specimens from patients. There was considerable variation in the detection rate of H. pylori DNA in salivary samples. The detection rate in saliva with the most effective primer pair was lower than that observed in feces, making saliva a less suitable specimen for the diagnosis of H. pylori infection. There is controversy regarding the permanent presence of H. pylori in saliva. Whether the salivary and gastric specimens of an individual harbor identical or different strains has not been resolved. PCR cannot distinguish between living and dead organisms. However, it can offer quick results on fecal and salivary specimens, which may contain fastidious and slow-growing H. pylori in low numbers.