Co-culture of Helicobacter pylori with oral microorganisms in human saliva

Helicobacter pylori is known for colonizing the gastric mucosa and instigating severe upper gastrointestinal diseases such as gastritis, gastroduodenal ulcers, and gastric cancer. To date, there is no data available on the oral cavity as transmission site, whether H. pylori can survive in the oral cavity or in human saliva. The aim of the study was to investigate the influence of oral microorganisms and human saliva on the survival of H. pylori in human saliva.

H. pylori strains KE, a motile derivate of type strain H. pylori 26695, and H. pylori SS1, a clinical isolate from a gastric biopsy, were grown in human pooled saliva (pooled from 4 healthy human donors, 0.22 μm filter-sterilized) or in BBF (Brucella browth formula; control) either as mono-cultures or in co-culture with Streptococcus mutans, Streptococcus oralis, Actinomyces naeslundii, Lacticaseibacillus casei and Candida dubliniensis. Bacterial survival of H. pylori and the oral microorganisms were investigated using colony forming units (CFU) assay and MALDI-TOF MS at baseline and after 24, 48 and 168 h.

In saliva, H. pylori KE demonstrated enhanced survival in co-culture with S. mutans, A. naeslundii, and C. dubliniensis, enduring for at least 48 h. In contrast, L. casei and S. oralis inhibited H. pylori KE in saliva. H. pylori KE could not be cultured after 168 h in saliva, neither in mono- nor co-culture. In contrast, H. pylori SS1 in saliva could be cultured after 168 h in co-culture with S. mutans and C. dubliniensis, but not in mono-culture. In BBF, H. pylori KE could be cultured after 168 h with S. mutans, L. casei and C. dubliniensis, and H. pylori SS1 with L. casei and C. dubliniensis, but not with S. mutans. Notably, the co-cultured microorganisms survived at high CFU numbers similar to those of the monocultures.

The study suggests that H. pylori can transiently survive in human saliva and even with presence of certain oral microorganisms. However, it may not be a permanent resident of the oral microbiota. The co-survival with oral microorganisms emphasizes the necessity for studying the role of the oral microbiota in the infectious and transmission cycle of H. pylori.