Scientists have identified the genes that the bacterium Salmonella typhimurium uses to make us ill.

Each year, nearly two million people around the world will die from a food-borne salmonella infection.

Researchers hope the new information will help them find novel ways of blocking the action of the rod-shaped microbes.

This has become a particularly urgent quest in recent years because some strains of the organism are now resistant to antibiotics.

The latest work, led by Dr Jay Hinton, at the Institute of Food Research (IFR) in Norwich, UK, comes just a year after scientists read the full DNA sequence of S. typhimurium.

All at once

Out of a total of 4,644 genes, his team was able to find the 919 that are activated during an infection.

About 400 of these genes are unknown to science - we have no idea what function they have.

"Some of these genes could be novel targets that you could hit that won't hurt [the patient]," Dr Hinton told BBC News Online.

The team used what is known as a DNA microarray to tell which genes were switched on and those that were switched off during various stages of the infection process.

"In one experiment you can actually see what is happening to all of the genes at once," Dr Hinton explained.

Managing to do this in the environment of infected cells is a world first.

'Real killers'

The work is published in the Molecular Microbiology Journal this month.

It will provide the starting point for many research groups around the world wanting to find drugs to counter salmonella infections.

The research also provides a template to investigate other pathogens, such as those responsible for malaria and tuberculosis.

Disease-causing genes can now be targeted in the development of new vaccines and antibiotics.

"This is the first time anyone has created a complete picture of gene expression for any organism during infection. It exposes which genes are the real killers. This new technique can be applied to any infectious disease," Dr Hinton said.

Main culprits

Salmonella takes its name from the discovery of the first strain in 1885 by an American veterinary surgeon, Daniel Salmon.

Today more than 2,200 varieties have been identified, but the majority of poisonings are caused by just two strains: S. typhimurium and S. enteritidis.

Salmonella lives in the stomach and intestines of humans and animals. It can lead to fever, abdominal pain, diarrhoea, nausea and vomiting.

In a number of cases the condition can become life-threatening - especially if the infection spreads to other parts of the body such as the blood or bone.

Most people will get a salmonella infection because they have eaten raw or undercooked contaminated food of animal origin - especially meat, poultry, eggs and milk.