To stay healthy, humans rely on a diverse community of viruses, fungi, and bacteria in their guts. Like Russian nesting dolls, our bodies contain about 38 trillion bacterial cells that make up our gut microbiome, and those cells have their own residents and so on. Most people are aware that this community of gut bacteria, or microbiota, plays a key role in healthy digestion, mental health, and immune function. But did you know that the human microbiome can also save lives? Below we reveal the latest research on how scientists discovered that not everyone gets sick from life-threatening infectious diseases like cholera – and that the answer may lie in a tiny bacterial organism.
What is Cholera?
Cholera outbreaks happen worldwide, from remote fishing villages in Cameroon, West Africa to more populated areas in Asia, Latin America, India, and the Middle East. According to the Centers for Disease Control and Prevention (CDC), the cholera bacterium, Vibrio cholerae, is usually found in water or food sources that have been contaminated by feces from a person infected with cholera. Cholera is most likely to be spread in places with inadequate water treatment, inept sanitation, and poor hygiene. A person can get cholera by drinking water or eating food contaminated with the cholera bacterium. Unfortunately, cholera can kill someone within hours if left untreated, and in 2018 499,447 cases were reported in 34 countries with 2,990 deaths. In the United States, there were 10 cases and no deaths (CNN Health, 2020).
How the Microbiome Aids in Resistance to Cholera
In the journal Cell, researchers uncovered how gut bacteria help some people resist cholera and the reason may surprise many. Microbiologist Ansel Hsiao, from the University of California – Riverside, studied whether the bacteria living in our microbiome can protect people from diseases caused by external bacteria such as Vibrio cholerae – which causes cholera. Hsiao’s team looked at the gut microbiomes from people in Bangladesh, where many suffer from the disease due to contaminated water and poor sanitation. Researchers wanted to see whether prior infections or other stresses, like malnutrition, make people more vulnerable compared to Americans who tend not to face these same pressures. The findings surprised the group as they found infection rates varied considerably among individuals in both populations. This finding suggests susceptibility is based on a person’s unique microbiome composition – and not where they live.
A Surprising Find
Vibrio cholerae, a rod-shaped organism, spends most of its time outside of humans and rarely encounter bile, which mammals produce to help digest fats after a meal. “Because bile is specific to the intestines of humans and animals, many microorganisms, including cholerae, have evolved ways to deal with it,” Hsiao states (Science Daily, 2020). Once Vibrio cholerae enters the body, the presence of bile and lack of oxygen in the gut triggers dormant genes, allowing it to survive in its human host. These genes are responsible for helping the bacterium to attach to intestinal walls and cause diarrhea. However, the real gamechanger happened when the team discovered another bacterium in the human microbiome – Blautia obeum. This bacterium can disable cholera’s disease-causing mechanisms, preventing it from hijacking the intestines. Blautia obeum produces a key enzyme that degrades salts in bile, which Vibrio cholerae uses as signals to control gene activity. When this occurs, the cholera-causing bacteria can not receive the signal to activate the dormant genes that cause infection.
What Does This Mean for the Future of Infectious Disease?
This research suggests new targets for individualized preventative strategies of the cholera infection through manipulating the structure of the gut microbiome. Now that we know having more Blautia obeum in the microbiome makes people less susceptible to cholera, future scientific studies will be focused on how to increase its presence in the gut. “We are extremely interested now in learning which environmental factors, such as diet, can boost levels of obeum,” Hsiao states. The microbiologist is also working with other groups trying to understand how the microbiome changes with COVID-19 infection, he explains “One day, we may also understand whether and how the microbiome affects COVID-19 and makes people resistant to other illnesses we don’t currently have treatments for.”
