Campylobacter remains the leading cause of bacterial foodborne illness in the UK and worldwide and despite decades of research, the poultry sector is still grappling with how best to control it. Now, new research suggests an unexpected player may be helping the bacterium survive and spread: amoebae.
Professor Brendan Wren and Dr Fauzy Nasher of the London School of Hygiene and Tropical Medicine spoke to Poultry Business to explain how their work may finally shed light on what they describe as the “Campylobacter conundrum”.
“Campylobacter is sensitive to oxygen. It doesn’t grow well in a natural environment,” says Wren. “It’s also not normally transmitted from person to person. So, it’s difficult to explain why it’s the biggest cause of foodborne disease worldwide.”
Yet it is everywhere, particularly in poultry. Studies have shown that up to 70% of supermarket chickens can carry the bacterium.
Once Campylobacter enters a bird, it thrives.
“When it gets into a chicken, it amplifies to trillions of cells in the gut,” says Wren. “Birds have a body temperature of 42 degrees, which is Campylobacter’s optimum growth temperature.”
Over millions of years, Campylobacter has evolved to exploit avian hosts with remarkable efficiency.
“The poultry chain is a major cause of Campylobacter food poisoning,” Wren explains. “The question is how it gets into poultry houses in the first place.”
The Amoeba hypothesis
The researchers believe the answer may lie in amoebae, which are single-celled organisms found widely in water and soil.
“Amoebae are omnipresent in the environment, particularly in water,” says Wren. “They feed on bacteria. That interaction has driven bacteria to evolve ways of surviving inside them.”
Through laboratory work, the team has shown that Campylobacter can survive inside amoebae and even emerge stronger.
“We’ve observed that when Campylobacter passes through amoebae, it becomes more invasive,” Nasher says. “It’s essentially more virulent than before.”
Professor Brendan Wren describes amoebae as acting like a biological delivery system.
“We think amoebae act as Trojan horses,” he says. “They carry Campylobacter into poultry houses, most likely via water.”
Not all Campylobacter survives the encounter with amoebae, but the bacteria that do may be better equipped to cause disease.
“If we start with 100 Campylobacter cells, around 70% are destroyed,” says Nasher. “But the ones that survive are more resilient. When they come out, they’re better at invading chicken cells and human cells.”
This may help explain why Campylobacter remains so persistent in the food chain despite biosecurity measures.
“In some ways, amoebae are training grounds for Campylobacter,” Nasher adds.
Campylobacter infections show a striking seasonal pattern, with cases rising sharply every summer.
“You see around a tenfold increase in the summer months, and it happens every year,” says Wren. “You can almost set your clock to it.”
Traditional explanations, such as increased barbecuing, don’t fully account for the trend.
“The peaks happen even in wet summers,” he says. “So that explanation doesn’t really hold.”
What does coincide with summer is an increase in amoebae. “However, amoebae bloom in the summer,” Nasher explains. “That fits very well with our hypothesis.”
Water treatment
Most poultry producers already treat water supplies, but amoebae may be slipping through those systems.
“Amoebae can form cysts,” says Nasher. “These are very hard shells that are extremely difficult to penetrate with UV or disinfectants.”
Campylobacter can survive inside those cysts. “That could explain why standard water treatment doesn’t fully eliminate the problem,” Wren says.
The team is now working directly with broiler poultry producers, including Wornham Farms in Hertfordshire, to investigate the issue in real-world settings.
“We’re monitoring farms with known Campylobacter outbreaks,” says Wren. “We’re taking water and environmental samples and detecting both amoebae and Campylobacter.”
They are want to collaborate with free-range producers, where contamination levels can be higher.
“Free-range systems tend to detect more Campylobacter,” Wren says. “That makes these farms particularly important for understanding what’s happening.”
If amoebae are confirmed as a key vector, intervention could be relatively straightforward.
“Simple treatments, like improved filtration, UV systems, or methods that specifically target amoebae and their cysts, could make a real difference,” says Nasher.
The researchers have recently had a paper accepted in Nature Communications Biology and are now seeking further funding to expand their on-farm trials.
“Our next step is to monitor farms across seasons and test intervention strategies in real time,” Nasher says.
While the idea that amoebae play a role in Campylobacter transmission isn’t entirely new, the researchers believe its significance has been underestimated.
“This idea has been around for decades,” says Wren. “But the importance of amoebae has been missed.”
“If we can intervene at the level of water and the wider farm environment,” says Wren, “we may finally be able to reduce Campylobacter where it really matters, before it reaches the bird.”