One of the most common causes of bacterial diarrhoea hides within another organism to protect itself from being destroyed by cleaning agents, writes Dick Ahlstrom
One of the nastiest of the food bugs has developed a clever way to protect itself from disinfectants and cleaning agents. It hides itself inside other single-celled organisms.
The microbe in question, Campylobacter, benefits in another way from this ruse. It uses the organism like a Trojan Horse, surviving in water supply systems long enough to cause further infection.
The hitch-hiking Campylobacter is a particular problem for intensively farmed chickens despite rigorous cleaning and disinfectant regimes, explains University of Ulster Coleraine scientist in the school of biomedical sciences, Dr Bill Snelling. The ability of the food bug to survive also raises the risk of excessive antibiotic use, something that could promote resistance to antibiotic use, he adds.
Campylobacter is a bad piece of work, he says. It is one of the most common causes of bacterial diarrhoeal illness in the developed world and produces estimated medical costs of $6bn (€4.8bn) a year in the US.
It is often contracted by eating undercooked chicken, says Dr Snelling. "It is a very dangerous bacterium which can cause diarrheal illness that can be life-threatening in sever cases."
Dr Snelling will spend from October to December working in Georgia, with the US department of agriculture, looking at the organism and its ability to hide in a variety of protozoans such as amoebas. He will work with collaborators to determine how the organism survives and resists by the protozoan and also whether the bug changes during its time inside.
Dr Snelling became interested in Campylobacter because of its persistence in agricultural units. "We could not understand how Campylobacter could survive since it is usually killed by disinfectants."
Dr Snelling and colleagues then discovered the bacteria hiding in their protozoan Trojan horses. "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," he explains. "We found many different protozoa in the farm water supplies of intensively reared poultry, and we also found the Campylobacter bacteria."
Laboratory experiments showed the organisms absorbed Campylobacter, but did not kill or digest them as expected. The bacteria can stay alive inside for about two days, even when disinfectant is added to the mix. Campylobacter outside on their own were readily killed by the chemicals.
"With Campylobacter we are not sure whether it is a physical barrier or if it changes phenotypically," says Dr Snelling. Recent work showed it may be able to survive inside the protozoan for longer than two days.
The work is important because other disease-causing bacteria may be using a similar mechanism to avoid cleaning agents and persist, allowing diseases to spread.
"In particular we need to find out how the bacteria convince the protozoa not to digest them. This could be a chemical signal, which we could identify and eventually override, allowing the protozoa to kill Campylobacter."
• The work at Coleraine was a collaboration with UU's Dr James Dooley, the local poultry industry and Dr John Moore of the Northern Ireland Public Health Laboratory, Belfast City Hospital.