Mycobacterium abscessus infection in the stomach of patients with various gastric symptoms.

Author summary The development of stomach diseases like gastritis, ulcer and cancer are associated with several factors, which include the colonized stomach bacteria, lifestyle, the environment and the host genes. Soon after its discovery, the stomach bacterium Helicobacter pylori were linked with stomach diseases like gastritis, stomach ulcer and cancer. However not all H. pylori infected individuals develop stomach disease, and not all patients with stomach disease have H. pylori infection. Initially, H. pylori were thought to be the only relevant bacterial coloniser of the human stomach, but several studies have shown that bacteria other than H. pylori can also colonise in human stomach. The role of these bacteria remained unclear, but it has been shown that the bacterial diversity in stomach differs depending on whether H. pylori is present or not. This work illustrates that Mycobacterium abscessus, a non-tuberculous bacteria is among the most frequently observed gastric bacteria in individuals with various stomach diseases and it is important to evaluate the significance of this infection. Development of gastric diseases such as gastritis, peptic ulcer and gastric cancer is often associated with several biotic and abiotic factors. Helicobacter pylori infection is such a well-known biotic factor. However, not all H. pylori-infected individuals develop gastric diseases and not all individuals with gastric diseases are infected with H. pylori. Therefore, it is possible that other gastric bacteria may contribute to the formation and progression of gastric disease. The aim of this study was to isolate prevalent gastric bacteria under microaerobic condition and identify them by 16S rRNA gene sequence analysis. Analysis of gastric biopsies showed infection of Mycobacterium abscessus (phylum Actinobacteria) to be highly prevalent in the stomachs of subjects included. Our data show that of 129 (67 male and 62 female) patients with gastric symptoms, 96 (51 male and 45 female) showed the presence of M. abscessus in stomach tissues. Infection of M. abscessus in gastric epithelium was further confirmed by imaging with acid fast staining, immunohistochemistry and immunofluorescence. Our imaging data strongly suggested that M. abscessus is an intracellular colonizer residing inside the gastric epithelial cells rather than in macrophages. Additionally, phylogenetic analysis of the mycobacterial hsp65 gene showed that the nearest match to the M. abscessus strains isolated from our study subjects is the M. abscessus strain ATCC 19977. Surprisingly, the subjects studied, the prevalence of M. abscessus infection in stomach is even higher than the prevalence of H. pylori infection. This, to the best of our knowledge, is the first study showing the colonization of M. abscessus in human gastric mucosa among patients with various gastric symptoms. This study could provide usher in a new opportunity to understand the role of less studied gastric bacteria in the development of gastric diseases.