Figure 3.

Oral niches of H. pylori and the reservoir controversy. (A) Candidate oral niches of H. pylori—dental plaque/biofilm, saliva, and the tongue dorsum—together with the oral genera relevant to its detection, including Porphyromonas. Three claims that this panel keeps distinct are the portal of entry (ingestion through the mouth), oral-oral transmission (person-to-person spread through saliva), and stable oral colonization as an extragastric reservoir; only the last requires viable, persisting organisms. Transmission routes: solid arrows denote the most frequently reported pattern (oral-oral), and dashed arrows denote proposed but less firmly established routes (gastro-oral and fecal-oral). (B, C) The competing evidence for (B) and against (C) the oral cavity as a stable H. pylori reservoir, weighed on a balance to convey that the evidence is mixed and context-dependent; plus and minus symbols mark supporting and opposing lines of evidence. Two notes beneath the balance record findings that fall on neither side. The absence of saliva-positive, biopsy-negative cases in the smaller pediatric cohort is equally predicted by an independent oral population and by gastric contamination; and in the larger pediatric cohort 68 of 342 gastric-negative children were saliva-positive, which shows that oral positivity can dissociate from gastric status without establishing viable or persistent oral colonization. The two recurring methodological problems that sustain the controversy are shown below; the first of these is that detection of H. pylori DNA establishes the presence of nucleic acid, not of viable or transmissible organisms. PCR, polymerase chain reaction; LAMP, loop-mediated isothermal amplification.