Nutrient Deficiency Promotes the Entry of Helicobacter pylori Cells into Candida Yeast Cells

SIMPLE SUMMARY: Helicobacter pylori is a pathogenic bacterium which causes several gastric and extra-gastric pathologies in humans. This pathogen is capable of entering eukaryotic cells of humans or of other species, including yeasts of the genus Candida. These yeasts are resistant to stressing environmental conditions (such as pH changes or scarce nutrients) which threaten the viability of H. pylori. Therefore, Candida yeasts may harbor this bacterium when subjected to stressing conditions or become transmission vehicles for it. Further research is required to establish the stressing environmental factors triggering the harboring of H. pylori within yeasts. The present work evaluated if deficiency or absence of the necessary nutrients favors the endosymbiotic relationship between these two microorganisms, facilitating the viability of the bacterium. In fact, a deficiency of nutrients increased the harboring of viable H. pylori cells within the yeast cells. On the contrary, in the complete absence of nutrients, the presence of intra-yeast bacteria was reduced. Therefore, yeast cells may contribute to the subsistence of this pathogenic bacterium when subjected to nutrient deficiency until it may infect an appropriate host, such as humans. The present work may also contribute, with further studies, to elucidate the transmission routes used by the pathogen H. pylori to infect its hosts. ABSTRACT: Helicobacter pylori, a Gram-negative bacterium, has as a natural niche the human gastric epithelium. This pathogen has been reported to enter into Candida yeast cells; however, factors triggering this endosymbiotic relationship remain unknown. The aim of this work was to evaluate in vitro if variations in nutrient concentration in the cultured medium trigger the internalization of H. pylori within Candida cells. We used H. pylori–Candida co-cultures in Brucella broth supplemented with 1%, 5% or 20% fetal bovine serum or in saline solution. Intra-yeast bacteria-like bodies (BLBs) were observed using optical microscopy, while intra-yeast BLBs were identified as H. pylori using FISH and PCR techniques. Intra-yeast H. pylori (BLBs) viability was confirmed using the LIVE/DEAD BacLight Bacterial Viability kit. Intra-yeast H. pylori was present in all combinations of bacteria–yeast strains co-cultured. However, the percentages of yeast cells harboring bacteria (Y-BLBs) varied according to nutrient concentrations and also were strain-dependent. In conclusion, reduced nutrients stresses H. pylori, promoting its entry into Candida cells. The starvation of both H. pylori and Candida strains reduced the percentages of Y-BLBs, suggesting that starving yeast cells may be less capable of harboring stressed H. pylori cells. Moreover, the endosymbiotic relationship between H. pylori and Candida is dependent on the strains co-cultured.