How H. pylori bacteria survive in the stomach

Bacterial binding to mucosa is acid-sensitive

“Such an attachment-detachment system is a great advantage,” says Asish Mukhopadhyay

An international group of over 50 scientists including three Indians have found out how the bacteria Helicobacter pylori survive in highly acidic environment of the human stomach. H. pylori causes peptic ulcer, and chronic infection can also lead to gastric cancer.

For the first time, scientists have found that the binding of the bacteria to the stomach mucosal layer is acid-sensitive, allowing it to attach and detach when needed. The bacteria bind to the mildly acidic (pH 6) mucous layer of the stomach and when the mucous is shed into the highly acidic (pH 2) stomach, the bacteria quickly unbinds and moves to a fresh mucous layer site. The results were published in Cell Host & Microbe.

Breakable binding

Previous studies have shown that the bacteria tightly attach to the epithelial cells and mucous of the stomach with the help of an adhesin called BabA. But now the researchers found that though tightly bound to the mucous, the binding affinity reduces once the bacteria sense more acidic pH (2-4 pH). The mucous lining of the stomach is constantly shed into the stomach, which is highly acidic compared with the mucous layer.

The scientists found a 2- and 20-fold less binding at pH 4 and 2, respectively, compared to pH 6. Within 30 seconds, 85% of the bacteria detached from the mucous layer when placed in a strong acid. They also saw that 95% of them recovered binding activity when shifted to less acidic site.

“Such a pH-dependent, reciprocal attachment-detachment system should be a great advantage for long-term colonization in the stomach. Indeed, its importance is supported by the extensive microevolution of BabA,” Dr. Asish K. Mukhopadhyay from the National Institute of Cholera and Enteric Diseases (NICED), Kolkata says in an e-mail to

The Hindu.

In order to know the exact pH at which bacteria loses binding, they tested 21 Swedish bacteria isolates. They found that that the bacteria detached at pH ranging from 2.3 to 4.9 showing that they can adapt to individual acid secretion patterns.

H. pylori is associated with low stomach acidity in Peru but higher acidity in Indians. The scientists carried out further studies to understand how Indian strains were more acid tolerant. They found that in order to escape the acid, the Indian strains attach to the end or bottom of the stomach.

Dr. Mukhopadhyay pointed out that future studies are required to fully understand the molecular mechanisms behind the Indian bacterial strains, and knowing how the bacteria attach and detach can help develop alternative medical aid for stomach diseases and rethink acid-supression therapies.