How Bacteria Get Past Our Defenses

This diagram shows how the bacteria Heliobacter pylori can penetrate the stomach lining.

Many researchers have further studied H. pylori, learning more about its structure, how it thrives, and even how it fends off stomach acid. Yet, until now, no one had explored how it traveled through the sticky gels of stomach mucus.

Conventional wisdom held that corkscrew-shaped H. pylori relies on its shape to twist and bore its way through mucus.

Instead, as part of the thesis of BU doctoral student Jonathan Celli, the researchers found that the bacteria swim in a manner more like other bacteria with whip-like tails; H. pylori just changes its environment to make movement possible.

"We figured out that it doesn't move like a corkscrew--everyone thought it did--and the same biochemistry that it uses for survival makes it possible for it to move," explained Bansil. "These two functions are inextricably coupled. It's chemically affecting its environment, and then it basically acts like a snowplow, moving by altering its surroundings."

H. pylori secretes the enzyme urease, which interacts with urea in the stomach to produce ammonia--the ammonia is what neutralizes the acids in the immediate environment. The less-acidic environment de-gels the mucin, allowing the microbe to travel through it using standard, flagella-based locomotion, much like other swimming bacteria.

To confirm their findings, the researchers placed H. pylori into an acidic mucin gel in a laboratory setting. While its flagella moved, the organism could not. After the microbes secreted urease and acidity diminished, the microbes were able to forge through the gel.

Bansil and her colleagues next want to understand the progress of H. pylori-related diseases, particularly in the context of living hosts. The team is planning to work on new imaging techniques that may reveal even greater detail about the organisms and how they inflict damage on the human body.

Jonathan Celli, supported by a National Science Foundation (NSF) Graduate STEM Fellows in K-12 Education (GK-12) fellowship, was lead author on the H. pylori findings, published in the Proceedings of the National Academy of Sciences on Aug. 11, 2009.

Rama Bansil's research was supported by the Independent Research/Development (IR/D) Program while serving in an Intergovernmental Personnel Act (IPA) assignment at NSF.

"A lot of scientists want to come to NSF at some point to give back and to participate in the other end of the funding scenario, but many people are concerned that taking such a long time out of their active research life would be a big hit," says Bansil. "While it is harder, it is possible--NSF actually has formal mechanisms to enable you to keep your research alive. That two-way dialog is very essential.  When people come here, they bring the university viewpioint to NSF, and when they go back, they help clear misconceptions. It helps build trust between the funding agency and the grantees."