5 April 2006
One of the most harmful bugs in the food chain is using tiny microbes as ‘Trojan Horses’ to shield itself from attack — and the result can be a serious case of food poisoning, according to University of Ulster research presented today.

Speaking at the Society for General Microbiology’s annual conference in Warwick, Dr Bill Snelling described how the extremely unpleasant food poisoning bacteria Campylobacter — which is often caught through eating undercooked chicken — is still common on intensive farms in spite of rigorous cleaning and disinfectant regimes.
Another worry is that this bug may become resistant to several antibiotics commonly used in human medicine, creating even more problems for doctors trying to treat this infection in patients with food poisoning.
“We could not understand how Campylobacter could survive since it is usually killed by disinfectants,” says Dr Snelling from the University’s School of Biomedical Sciences.
“It is a very dangerous bacterium which can cause diarrhoeal illness that can be life threatening in severe cases. Currently it is the most common cause of bacterial diarrhoea in developed countries like Britain”.
“We discovered that the bacteria are hiding in Trojan horses called protozoa. This group of larger microbes, which live in water and feed on bacteria, are like the ones you can see through microscopes when you go pond dipping as a child”, says Dr Snelling. “We found many different protozoa in the farm water supplies of intensively reared poultry, and we also found the Campylobacter bacteria”.
The scientists discovered through laboratory experiments that protozoa will absorb Campylobacter, but do not kill or digest them as expected. The bacteria can stay alive inside the protozoa for about two days, even when disinfectant is added. If Campylobacter were disinfected without any protozoa present then they were quickly killed.
In the developed world, Campylobacter is the most common cause of bacterial diarrhoeal illness, and is estimated to cost up to $6 billion every year in the USA alone in medical costs and lost working hours. Most sufferers from the illness recover quickly, but some can go on to have long-term problems such as arthritis or Guillain-BarrÈ Syndrome which affects the immune system.
If Campylobacter can use protozoa as a protection against harsh environmental conditions — such as cleaning and disinfection — then other disease causing bacteria may be using a similar mechanism. It is possible that many other diseases may be spread the same way.
“We are now looking at further investigations, such as whether Campylobacter are changed by their time inside the protozoa. For instance they might become more virulent for humans after the experience, or they may become better at infecting chickens,” says Dr Snelling.
“In particular we need to find out how the bacteria convince the protozoa not to digest them. This might be a chemical signal, which we could identify and eventually override, allowing the protozoa to kill Campylobacter. This would be a new form of biocontrol and would help reduce the use of disinfectants and antibiotics in agriculture.
“Reducing the incidence of Campylobacter poisoning will reduce a lot of human suffering. We have highlighted a new reservoir of this important disease-causing bacteria. This is a significant step towards eliminating these bacteria from the food chain. Now we understand where the organism hides we can design better systems to kill it”.