Vacuoles of Candida yeast as a specialized niche for Helicobacter pylori

Abstract

Helicobacter pylori (H. pylori) are resistant to hostile gastric environments and antibiotic therapy, reflecting the possibility that they are protected by an ecological niche, such as inside the vacuoles of human epithelial and immune cells. Candida yeast may also provide such an alternative niche, as fluorescently labeled H. pylori were observed as fast-moving and viable bacterium-like bodies inside the vacuoles of gastric, oral, vaginal and foodborne Candida yeasts. In addition, H. pylori-specific genes and proteins were detected in samples extracted from these yeasts. The H. pylori present within these yeasts produce peroxiredoxin and thiol peroxidase, providing the ability to detoxify oxygen metabolites formed in immune cells. Furthermore, these bacteria produce urease and VacA, two virulence determinants of H. pylori that influence phago-lysosome fusion and bacterial survival in macrophages. Microscopic observations of H. pylori cells in new generations of yeasts along with amplification of H. pylori-specific genes from consecutive generations indicate that new yeasts can inherit the intracellular H. pylori as part of their vacuolar content. Accordingly, it is proposed that yeast vacuoles serve as a sophisticated niche that protects H. pylori against the environmental stresses and provides essential nutrients, including ergosterol, for its growth and multiplication. This intracellular establishment inside the yeast vacuole likely occurred long ago, leading to the adaptation of H. pylori to persist in phagocytic cells. The presence of these bacteria within yeasts, including foodborne yeasts, along with the vertical transmission of yeasts from mother to neonate, provide explanations for the persistence and propagation of H. pylori in the human population. This Topic Highlight reviews and discusses recent evidence regarding the evolutionary adaptation of H. pylori to thrive in host cell vacuoles.

Keywords: Helicobacter pylori, Intracellular, Candida, Vacuole

Core tip:Helicobacter pylori (H. pylori) have been observed within yeast vacuoles by light and fluorescence microscopy, and their presence has been confirmed by the detection of H. pylori-specific genes and proteins in yeast extracts, such as VacA subunits, UreA, peroxiredoxin and thiol peroxidase. Moreover, non-culturable H. pylori cells have been found in subsequent generations of yeasts, indicating the generational transmission of the bacteria is part of the transfer of vacuolar content. H. pylori are therefore well-equipped to establish in the vacuoles of yeast, which provide them with essential nutrients such as ergosterol for multiplication, as a pre-adaptation for invasion of human cells.