The bacteria in the gut provide information about the amount of fungi belonging to the genus Candida that are potentially pathogenic. Surprisingly, they contain lactic acid bacteria, which are known for their ability to protect against fungal diseases. Researchers at the Leibniz Institute for Natural Product Research and Infectious Biology (Leibniz-HKI) and its Danish and Hungarian collaborators have added another piece to the puzzle of understanding the human gut microbiome.
The human gut microbiome is a highly complex community in which many microbes regulate each other. If there is an imbalance as a result of antibiotics or other environmental effects, individual species can spread and cause infection. For example, Candida fungi are found in the intestines of many healthy individuals. They are usually harmless, but have the potential to cause serious systemic infections. Studying these interactions in the gut is difficult. Several hundred species of bacteria and fungi can only partially be cultivated in the laboratory, and many more are unknown. Researchers at Leibniz-HKI are trying to shed more light on the gut using metagenome studies.
For a study just published in Nature Communications, researchers analyzed stool samples from 75 cancer patients and found that certain bacterial species always appeared in greater numbers when the levels of fungi belonging to the genus Candida were high. „With these data, we developed a computer model that could predict Candida levels in another group of patients with 80 percent accuracy based on bacterial species and amounts alone,” explained Bastian Seelbinder, lead author of the study. These bacteria mainly include oxygen-tolerant species. Sealbinder conducts research in Gianni Panagiotou’s Department of Microbiome Dynamics at Leibniz-HKI, with a strong focus on the gut microbiome. What surprised the researchers was not only how successful the amount of fungi was based on the bacterial species present, but also which bacteria associated with the highest amount of fungi. „We found a number of bacterial species that produce lactic acid, including Lactobacillus species,” explains Seelpinder. It was a discovery he did not expect. „I couldn’t believe it at first, so I checked several times, always with the same result.”
The reason for his surprise: several studies have confirmed the protective effect of lactic acid bacteria against fungal infections. One of them was published last year by Panagiotou’s group, also in the journal Nature Communications. „The result shows again how complex the human gut microbiome is and how difficult it is to understand the interactions of different microbes,” Panagiotto said. Researchers’ claim: Lactic acid bacteria, especially those belonging to the genus Lactobacillus, support Candida proliferation, but at the same time make the fungus less virulent. This may be because Candida species can change their metabolism to use lactate produced by lactic acid bacteria. As the researchers discovered in additional experiments, this gives them a competitive advantage over other fungi such as Saccharomyces cerevisiae. However, the metabolic switch causes Candida to remain in its normally harmless spherical yeast form instead of forming fungal hyphae that can invade the intestinal mucosa.
„There is also the suggestion that certain groups of Lactobacillus species may have different effects,” Seelpinder said. To investigate this, the next step is to carry out detailed genetic analyzes of the bacteria. „For the current study, we examined stool samples from cancer patients who are particularly at risk for fungal infections,” Panagiotto explains. For further studies, samples from healthy subjects could be included to develop long-term strategies for at-risk patients based on their microbiome. (ANI)
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