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Helicobacter pylori

Following the accidental abandonment of incubated plates, H. pylori colonies were discovered, launching a larger investigation into the microbiology of the human stomach. More research is needed on this disease-causing gram-negative bacterium, but we provide the basics of its characteristics, transmission routes, and prevention.

Would you like to listen to the podcast version of this article instead? Check out the Wee Beasties Podcast Helicobacter pylori episode

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The origin of Helicobacter pylori

Helicobacter pylori is a spiral-shaped bacteria that makes a home in your stomach, causing ulcers and even stomach cancer, in some cases. According to a 2013 report1 in Nature, H. pylori is the most widespread infection in the world, infecting at least half of the global population. In 1994, The World Health Organization (WHO) recognized H. pylori as a group one carcinogen, but the backstory on this little bug isn’t that straight forward. H. pylori was discovered more recently, in comparison to the other microorganisms we’ve discussed. It was discovered in 1983, and it was first found as a colony in the human stomach in a stroke of luck after two doctors were trying to demonstrate a connection between the severity of gastric distress experienced by their patients and the number of bacteria present. The two Australian doctors credited with the discovery mistakenly left a plate in the incubator a lot longer than intended, and they happen to get H. pylori colonies on it. Those that have worked with H. pylori before know just how persnickety the bacteria is, and that it is exceedingly difficult to grow outside of its habitat. In part, this discovery prompted scientists to begin a larger investigation into the microbiology of the human stomach using 16S rRNA analysis, and now we know that the stomach and the rest of the human gut has an extraordinarily diverse microbiome of bacteria which is critical to our immune response and other autonomic faculties.

1 Salama, N., Hartung, M. & Müller, A. Life in the human stomach: persistence strategies of the bacterial pathogen Helicobacter pylori. Nat Rev Microbiol 11, 385–399 (2013). https://doi.org/10.1038/nrmicro3016

Notable characteristics of Helicobacter pylori

Similarly to the other pathogens we’ve discussed, H. pylori is a gram-negative bacterium, meaning it has that extra lipopolysaccharide (LPS) barrier on its outer membrane. So, for starters, it’s more protected simply by its composition as a gram-negative bacterium. However, H. pylori has a cool mechanism that allows it to transform its shape when it’s under stress. Examples of stress may include a change in pH or salinity, or an increase in the gases present, such as nitrogen, carbon dioxide, and oxygen.

Environments of Helicobacter pylori

As mentioned before, H. pylori is difficult to grow on a plate outside its ideal habitat. Even in its ideal habitat, the stomach, the bacterium only thrives in specific conditions of pH and gas, and any deviation from those conditions will cause the cells to become dormant and change shape. H. pylori is spiral or helix-shaped, hence the “Helicobacter” name. The bacteria needs to burrow into the epithelium within the stomach lining to survive, so it uses its spiral shape and several flagella to corkscrew itself into our stomach to take residence. However, if the cell becomes stressed due to a change in any of those conditions, pH, salt, gas, or temperature, it will slow down its metabolic machinery and change from its spiral shape and into a coccoid form. It’s still unclear if this transformation under stress is a selected adaptation. Several studies point to H. pylori’s transformation as an evolutionary adaptation to cope with stress, while others show no relationship. There needs to be more experiments to tease this out, but it’s clear that a viable but non-culturable (VBNC) state is common with H. pylori, making this a difficult organism to culture from biopsies.

Patient risk associated with Helicobacter pylori

H. pylori is still a bit mysterious, and not always well characterized to researchers. Contaminated water sources are certainly a means of infection, but so is fecal-oral and mucous-oral routes. This can result from living in close quarters with a large community and not having access to proper disinfectants on touchable surfaces. Once one person in a close-quarters household acquires H. pylori, the R0, the rate of infection to other individuals, in that sample size will increase over time. Since H. pylori is challenging to culture, one of the most reliable ways to detect and study H. pylori is with molecular diagnostic tools using 16S rRNA and qPCR. We’ve talked about pathogens that cause pneumonia and acute respiratory infections, ones that infect the blood, and now we have a pathogen that infects your gut with little to no indication of infection in most patients. Though worldwide infection rates are going down, largely because of access to clean water and surface disinfectants, the best way we can track and surveil this pathogen is by using these new diagnostic tools.

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