Table 2.
Candidate oral and salivary microbial taxa as non-invasive signatures, with the target condition, reference standard, and reported diagnostic accuracy for each.
| Taxon | Direction | Target condition (reference standard) | Evidence population (design, n) | Specimen; platform | Reported diagnostic accuracy | Grade (population, phase) | Reference |
|---|---|---|---|---|---|---|---|
| Pediatric evidence | |||||||
| Porphyromonas | Increased | Oral H. pylori carriage (oral PCR; no gastric reference standard) | Pediatric and adult; cross-sectional; 21 children | Saliva, dental plaque; 16S rRNA gene sequencing | NR (community comparison only) | Pediatric, Phase 1 | (Ogaya et al., 2024) |
| Adult-derived evidence; not evaluated in children | |||||||
| Campylobacter concisus | Increased | Gastritis and precancerous cascade (endoscopy with histopathology) | Adult; 78 gastritis and 50 controls, plus 38-patient detection cohort | Tongue coating, gastric fluid; shotgun metagenomics, qPCR | NR | Adult, Phase 1 | (Cui et al., 2019); cross-reaction caution (Scholz et al., 2025) |
| Fusobacterium (F. nucleatum) | Increased in gastric cancer; decreased in H. pylori-negative gastritis saliva | Gastric carcinogenesis; H. pylori-negative chronic gastritis (gastric histopathology) | Adult; n per taxon NR | Gastric mucosa, saliva; 16S rRNA gene sequencing, qPCR | NR | Adult, Phase 1 | (Coker et al., 2018; Contaldo et al., 2021) |
| Prevotella | Increased | Gastric cancer; H. pylori-negative gastritis (gastric histopathology) | Adult; n per taxon NR | Gastric mucosa, saliva; 16S rRNA gene sequencing | NR | Adult, Phase 1 | (Ferreira et al., 2018; Hsieh et al., 2018; Zhang et al., 2023) |
| Veillonella | Increased | Gastric cancer and precancerous cascade (gastric histopathology) | Adult; n per taxon NR | Gastric mucosa; 16S rRNA gene sequencing | NR | Adult, Phase 1 | (Castaño-Rodríguez et al., 2017; Chattopadhyay et al., 2023) |
| Streptococcus | Increased | Gastric cancer; gastritis (gastric histopathology) | Adult; n per taxon NR | Gastric mucosa, saliva; 16S rRNA gene sequencing | NR | Adult, Phase 1 | (Zhang et al., 2023; Yang et al., 2025) |
| Parvimonas | Increased | Gastric carcinogenesis (gastric histopathology) | Adult; n per taxon NR | Gastric mucosa; 16S rRNA gene sequencing | NR | Adult, Phase 1 | (Coker et al., 2018) |
| Peptostreptococcus | Increased | Gastric carcinogenesis (gastric histopathology) | Adult; n per taxon NR | Gastric mucosa; 16S rRNA gene sequencing | NR | Adult, Phase 1 | (Ferreira et al., 2018) |
| Neisseria | Increased | H. pylori-negative gastritis (gastric histopathology) | Adult; n per taxon NR | Gastric mucosa; 16S rRNA gene sequencing | NR | Adult, Phase 1 | (Hsieh et al., 2018; Zhang et al., 2023) |
Direction indicates the reported change in the diseased state. Each candidate is tied to the target condition against which it was actually evaluated and to the reference standard used; NR indicates that the primary study did not report sensitivity, specificity, or an area under the curve for that target condition and population. Grades follow the two axes defined in Section 2. With the single exception of Porphyromonas, every taxon here is supported only by adult data, which is the review’s central gap statement; adult-derived entries are grouped separately for that reason and are not directly comparable with the pediatric entry. Several taxa change direction with disease context—Fusobacterium, for instance, is enriched in gastric cancer yet reduced in H. pylori-negative gastritis saliva, which is precisely why no single taxon can serve as a stand-alone classifier. No head-to-head comparison of these taxa in a common population has been reported, so no candidate is ranked against another. GC, gastric cancer; NR, not reported. A meta-analytic eight-taxon mucosal classifier incorporating several of these genera reached an area under the curve of 0.85 for gastric cancer versus superficial gastritis, but accuracy has not been reported for any single genus.