Scientists reveal clues to food poisoning bug

Scientists have identified the genetic make-up of the bug responsible for the majority of food poisoning outbreaks. The work paves the way for treatments that may eventually prevent or cure gastro-enteritis attacks that are, at best, extremely unpleasant, and, at worst, can kill.

A team of researchers, led by Dr. Julian Parkhill at the Sanger Centre, near Cambridge, has completed the genome sequence of Campylobacter jejuni. Funding for the project, the results of which are published in Nature (10 February), has come from the Wellcome Trust through its Beowulf initiative.

The first food-borne pathogen to be sequenced, C. jejuni is harboured by half of the poultry destined for human consumption. It is responsible for around 60,000 reported cases of food poisoning in the UK each year – over three times more than the infamous Salmonella. The bacterium thrives in the human gut where it can cause severe diarrhoea and, in rare cases, Guillain-Barre syndrome, a neuromuscular condition that can lead to death.

The Sanger team, alongside Professor Brendan Wren at the London School of Hygiene and Tropical Medicine and Dr. Julian Ketley of Leicester University, has spent two years sequencing the 1,641,481 base pairs (nucleotides) of the C. jejuni genome. Among the findings are an estimated 1,654 genes that code for proteins, representing 94.3% of the genome. This makes the organism the most gene-dense bacterium yet sequenced.

One of the interesting features to emerge is a very high level of genetic variation, particularly in genes for sugar molecules present on the bacterial cell surface. This rate of variation is more commonly seen in viruses rather than bacteria and may be responsible for C. jejuni’s ability to reside in the inhospitable environment of the gut.

The researchers also identified sets of genes involved in the production of sialic acid on the cell surface. These molecules are thought to help C. jejuni avoid the body’s immune response or may trick the body into launching an attack against itself, as happens in Guillain-Barre syndrome.

“This is the first food-borne pathogen to be completely sequenced. These data have revealed many novel mechanisms by which the organism survives and proliferates both inside and outside the host and how it causes disease. Armed with this new wealth of information, scientists hope to devise intervention strategies to eliminate the organism from the food chain.”

Professor Brendan Wren at the London School of Hygiene and Tropical Medicine

“The availability of our results to interested scientists worldwide as soon as they were produced has been of enormous value in the battle against this organism.”

Dr. Julian Parkhill Project leader, the Sanger Centre

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Notes to Editor

  1. The Sanger Centre is one of the world’s leading genome sequencing centres. Both the Sanger Centre and the Wellcome Trust have been at the forefront of efforts to keep sequence data in the public domain. Websites: www.sanger.ac.uk; www.wellcome.ac.uk/en/1/biovengensan.html

  2. Beowulf Genomics is a non-profit collaborative initiative set up by the Wellcome Trust to sequence the genomes of bacteria and parasites which cause some of the world’s most significant infectious diseases. Website: www.beowulf.org.uk

  3. The Wellcome Trust is the world’s largest medical research charity with an annual spend of some £600 million in the current financial year 1999/2000. The Wellcome Trust supports more than 3,000 researchers at 300 locations in 30 different countries – laying the foundations for the healthcare advances of the 21st century and helping to maintain the UK’s reputation as one of the world’s leading scientific nations. As well as funding major initiatives in the public understanding of science, the Wellcome Trust is the country’s leading supporter of research into the history of medicine.

  4. The DNA of every living organism is made up of four chemical ‘bases’ represented by the letters A, C, G, T. The bases are paired together, A with T and C with G to produce double-stranded DNA in the familiar helix. The number of bases vary from a few thousand to several million depending on the size of the organism. They carry the genetic instructions and occur in linear form like beads along a string. Determining the length and order of these letters is known as sequencing.