A recent systematic review concluded that oral malodor is reduced by eradication of H. pylori [26]. However, most of the studies included in that review assessed subjective symptoms of oral malodor using a questionnaire [11, 12, 27, 28]. This is the first study to measure VSC concentrations by GC and to perform the OLT to evaluate the effect of H. pylori eradication on oral malodor objectively. As a result, the OLT score was significantly decreased after H. pylori eradication compared with baseline. In contrast, the concentrations of H2S and CH3SCH3 were decreased on the date of eradication compared with baseline, albeit not significantly so. In addition to VSCs, ammonia, methylamine, dimethylamine, propionic acid, butyric acid, indole, skatole, and cadaverine may cause oral malodor [29]. Additional studies on the involvement of substances other than VSCs in oral malodor associated with H. pylori are needed. After initiating the primary eradication regimen, there were differences in clinical findings and the proportions of some bacterial species between the success and failure groups. We suggest that these differences may be key to successful eradication.
The amelioration of oral malodor was not due to a direct effect of antibiotics on oral bacteria, because the bacterial composition was not different from that before eradication, and the total oral bacterial count was not significantly different between after H. pylori eradication and baseline. Use of antibiotics in combination with mechanical therapy for periodontal disease resulted in significant differences in the richness and dissimilarity of the oral microbiota after 2 months, whereas the evenness and diversity were not affected [30]. It is possible that the effect on the oral microbiota differs between antibiotics alone and antibiotics plus mechanical therapy.
The ability of H. pylori to produce H2S and CH3SH is strain-specific [31]. H. pylori has been detected in oral specimens [6, 7, 32], and its prevalence was associated with the progression of periodontitis. There is disagreement as to whether H. pylori is present in the oral cavity. The bacterial communities in the oral cavity are highly complex and include a large number of VSC-producing bacteria [2]. The oral malodor associated with H. pylori is unlikely to be caused by its production of VSCs but, rather, by exacerbation of periodontitis and changes in the populations of some oral bacteria. Chronic systemic inflammation and periodontitis interact via the systemic inflammatory response [33]. Thus, irrespective of the presence or absence of H. pylori infection in the oral cavity, gastric inflammation may exacerbate oral malodor via periodontitis.