Bacteria change ‘fingerprints’ and baffle detectives

Tracing the source of a campylobacter food poisoning outbreak can be very difficult even with modern DNA fingerprinting methods. There is now evidence that campylobacters can rearrange their DNA, disguising their fingerprint, and confusing such detective work, scientists heard today (Tuesday 09 April 2002) at the spring meeting of the Society for General Microbiology at the University of Warwick.

Professor Diane Newell and her colleague Dr Anne Ridley of the Veterinary Laboratories Agency say, “We can only track campylobacter strains, for example from food to human infection, using a DNA fingerprinting method if the strain type stays stable over time and geographical distance. DNA changes can have an observable effect on the type that is identified. We call this genotypic instability.”

Genotypic instability may have a big advantage for the campylobacter. DNA rearrangements may be involved in helping the bacteria survive in hostile environments and providing strain variants that can colonise chickens and other animals better.

Professor Newell explains, “We’ve found that chicks are campylobacter-free when they are born but they become infected within 2-3 weeks of life. In order to control infection in poultry flocks, methods are required to track infecting strains all over the farm to the finished poultry product sitting in the fridge at home.”

“The most effective way to control campylobacter food poisoning would be to stop chicks becoming infected. Our research has shown that good hygiene is not enough to keep campylobacters out of farms and broiler houses. An alternative approach would be to use `friendly` campylobacters that can infect chicks but not cause disease in humans, which would exclude any harmful campylobacters,” says Professor Newell.