SALMONELLA food poisoning causes infection in about 20 million people worldwide each year and is responsible for about 200,000 human deaths. It also infects farm animals and attaches to salad vegetables.

In groundbreaking research recently, scientists have shown what the food-poisoning bacterium uses as food to survive as it causes infection. It eats glucose.

Now, their discovery of salmonella's need for sugar could provide a new way to vaccinate against it. The finding could also lead to vaccine strains to protect against other disease-causing bacteria, including hospital-resistant "super-bugs" such as MRSA (methicillin-resistant Staphylococcus aureus).

"This is the first time that anyone has identified the nutrients that sustain salmonella while it is infecting a host's body," said Dr Arthur Thompson from the Institute of Food Research in the United Kingdom.

The nutrition of bacteria during infection is an emerging science and this is one of the first major breakthroughs, achieved in collaboration with Dr Gary Rowley at the University of East Anglia, at Norwich, eastern England.

During infection, salmonella bacteria are engulfed by immune cells designed to kill them. But, instead of that happening, the bacteria multiply.Salmonella must acquire nutrients to replicate. The scientists focused on glycolysis, the process by which sugars are broken down to create chemical energy.

They constructed salmonella mutants unable to transport glucose into the immune cells they occupy and unable to use glucose as food. These mutant strains lost their ability to replicate within immune cells, rendering them harmless.

"Our experiments showed that glucose is the major sugar used by salmonella during infection," said Dr Thompson.

The mutant strains still stimulate the immune system and the scientists have filed patents on these that could be used to develop vaccines to protect people and animals against poisoning by fully virulent salmonella.

Glycolysis occurs in most organisms including other bacteria that occupy host cells. Disrupting how the bacteria metabolise glucose could therefore be used to create vaccine strains for other pathogenic bacteria, including some super-bugs.

The harmless strains could also be used as vaccine vectors. For example, the influenza gene could be expressed within the harmless salmonella strain and safely delivered to the immune system.The next stage of the research will be to test whether the mutants elicit a protective immune response in mice.

Salmonella is a type of bacteria usually found in poultry, eggs, unprocessed milk and in meat and water. It may also be carried by pets such as turtles and birds.

The salmonella bacteria attack the stomach and intestines. In more serious cases, the bacteria may enter the lymph tracts that carry water and protein to the blood, and the blood itself. The bacteria attack all age groups and both sexes. Children, the elderly and people who are already ill are much more likely to get a serious infection.

In Germany the nutrition of bacteria is the subject of a six-year priority programme of research to investigate how bacteria are able to multiply inside a host's body to cause disease.

The Institute of Food Research (IFR) is an institute of the Biotechnology & Biological Sciences Research Council (BBSRC). This research was funded by a core strategic grant from the BBSRC.

The Institute of Food Research undertakes international quality scientific research relevant to food and human health and works in partnership with others to provide underpinning science for consumers, policy makers, the food industry and academia. It is grant aided by the Biotechnology & Biological Sciences Research Council (www.bbsrc.ac.uk/)