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Helicobacter pylori is a bacterium that infects the human stomach. It has done so since modern humans evolved in Africa and about half the world's population carries the bacterium. Most people never realise they are infected, but in some the chronic inflammation leads to peptic ulcers and, in the worst cases, stomach cancer, a disease that kills nearly a million people every year.

Record-breaking study

“The stomach infection can be treated with antibiotics, but because the bacterium is so widespread, it is not possible to treat everyone who has it. Therefore, we need to understand more about which bacterial characteristics increase the risk of gastric cancer,” says Kaisa Thorell, Associate Professor at the University 91̽�� and one of the lead authors of a new record-breaking study of Helicobacter pylori now published in the journal Nature.

The study mapped the genome of the stomach bacterium from nearly 9,000 people from all corners of the world to investigate the spread of the bacterium. The analysis revealed a new variant of the bacterium that had not previously been described.

“The new type of bacteria has different characteristics, for example, it seems to bind to the cells of the stomach in a different way than the previously known type. The variant is now most common in indigenous populations in the Americas and northern Asia,” says Kaisa Thorell.

Specialised for carnivores?

The authors hypothesise that the new strain specialises in living in the stomachs of people whose diet consists mainly of meat or fish. The reason is the bacterium's specialised gene set and that it is closely related to a stomach bacterium that infects large carnivorous felines, such as lions.

“However, we believe that the variant has been present in more places on Earth as we can show that it evolved even before humans migrated out of Africa. Our analysis shows that both variants have travelled with humans since the emergence of our species in Africa more than 200 000 years ago. If the newly discovered variant is adapted to carnivores, it shows that the people who migrated from Africa had limited access to food from the plant kingdom.”

Lives in the gut for decades

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The researchers have named the newly discovered variant of Helicobacter pylori ‘Hardy’, as in harsh living conditions. The indigenous people living with this variant of the bacterium live in places where plant-based foods such as fruit, berries and vegetables, which reduce the risk of stomach cancer, have been scarce for much of the year.

“The bacterium can live in our stomachs for decades, in a constant ongoing interaction with the human immune system, which can result in stomach diseases. What fascinates me is that the Hardy type seems to have a completely different strategy for interacting with its host. We will now go on to study the ‘Hardy bacterium’ in detail, which may give us new insights into the development of stomach diseases, including the often fatal stomach cancer,” says Kaisa Thorell.

Scientific article in Nature:

91̽��: Kaisa Thorell, Associate Professor, at the Department of Chemistry and Molecular Biology at the University 91̽��, phone: 070-321 29 46, e-mail: kaisa.thorell@gu.se