How salmonella uses body’s own defences to spread infection

A study at Edinburgh University has found that the bacterium has a mechanism that it uses to change the nature of key cells that line the intestine, enabling the bugs to gain access to the body, spreading infection.

The discovery has long-term potential for developing vaccines against the bacteria, but also boosting the body’s immune system.

Salmonella food poisoning – commonly caused by eating undercooked poultry or eggs – is a serious infection that can lead to diarrhoea, fever and even death in young children.

In 2011, there were 737 recorded incidents of salmonella poisoning in Scotland, compared with 941 in 2010.

In February this year, 35 people in the UK, including five in Scotland, were hit during an outbreak linked to infected slices of ready-to-eat watermelons. It resulted in one death.

According to Dr Neil Mabbott, who worked on the three-year research project, salmonella targets the immune system’s own monitoring system of the intestine to get access to the body.

“The intestine is usually designed for keeping bacteria and other pathogens out but taking in food molecules,” he explained.

“In occasional places along it [the intestine], the immune system needs to be able to sample what’s going on in the intestine, to discover if there’s an infection going on, and respond to it. There are specialised cells to do this called M-cells – microfold cells – that are essentially designed for taking up large particles, which could be toxins or bacteria, so that the immune system can sample them and decide whether they are friend or foe and act accordingly.”

The research showed that salmonella bacteria change the make-up of intestine cells, turning them into these M-cells and effectively creating a “portal” out into the body where they can infect vital organs, such as the kidneys and the liver.

The salmonella injects a protein called SopB into cells in the lining of the intestinal wall, called epithelia – which transforms the make-up of certain ones, creating a dramatic increase in M cells.

The work, published in Cell Host & Microbe, reveals how, once the salmonella produces enough cells, it can then get through into the bloodstream.

It was previously suspected that salmonella was using these M-cells to get into the body, but the mechanism by which it was doing this was not understood.

Scientists say that the research significantly furthers our understanding of bacterial infections.

As part of their study, the Edinburgh scientists showed that the protein used by salmonella can be artificially disabled, reducing greatly its ability to spread out into the body.

This raises the potential for developing vaccinations against the infection. However, it is also hoped that the “transformation” protein mechanism could be harnessed and used to boost the body’s immune system.

Lead researcher Dr Arvind Mahajan, from the Roslin Institute, said yesterday the study revealed the “sophisticated” way that bacteria adapted their environment to their own ends.