Playing chicken with Campylobacter

Campylobacter jejuni is the most common agent of food poisoning in industrialised nations. Professor Gary Dykes' team at Monash University is trying to understand how it not only survives, but how it persists under conditions that should kill it

Potentially deadly pathogenic strains of Salmonella and Escherichia coli get most of the headlines, but Professor Gary Dykes says most cases of non-lethal food poisoning in Australia are due to diners running afoul of poorly cooked chicken, and its microbial hanger-on, Campylobacter.

It’s the hanger-on part that sparked the interest of the Monash University microbiologist, who is an invited speaker at the Australian Society of Microbiology annual conference in Melbourne in July.

The various species of Campylobacter - 18 have been described to date - are delicate organisms that colonise the intestines of livestock species and live harmlessly as members of their commensal gut flora. Dykes says they are very fastidious in their requirements for survival and growth.

How, then, do they manage to survive and multiply outside the host animal’s body, despite the use of chemical and physical measures to prevent contamination as meat moves through the food-processing chain from the slaughterhouse to the kitchen?

Living in the fridge

Campylobacter is one of the most common causes of food-poisoning diarrhoea in humans around the world.

In industrialised nations, Campylobacter food poisoning occurs at an annual rate of between 20 and 150 cases per 100,000 people. Most human infections involve C. jejuni, a commensal species in chickens that survives in raw and undercooked chicken.

Dykes and his colleagues at Monash University have been trying to determine how Campylobacter manages to attach and survive on exposed food processing surfaces and uncooked meat after animals are slaughtered. All this without succumbing to conditions that are unfavourable for them, such as the high levels of oxygen in air.

He says Campylobacter thrives in an environment that contains less than 5% oxygen - well below the natural 20.95% concentration in air.

Paradoxically, despite its preference for living in the warmth of the intestinal tract, Campylobacter struggles to survive at temperatures higher than 20° Celsius outside the body.

In fact, Dykes says, Campylobacter does best at the near-freezing temperatures of refrigeration, inside vacuum packs - conditions that strongly inhibit growth of other food-poisoning microbes like Salmonella and E. coli.

Understanding colonisation

Many bacteria have the ability to integrate with other species that form persistent, mixed-species communities on surfaces, called biofilms - Dykes says research teams elsewhere have shown that Campylobacter has the ability to form biofilms on its own, or as part of complex microbial communities.

His group’s research specialisation is understanding how pathogens attach to and colonise surfaces, which may lead to novel biochemical compounds or surface treatments that will limit attachment and colonisation, reducing the frequency of food-poisoning episodes.

“We’ve identified some plant-derived compounds that can be used to coat surfaces that are very effective at preventing attachment,” he said. “They’re fairly innocuous tannin-based molecules that attach well to food surfaces and influence hydrophobicity and surface charge.

“We have other compounds that strip off bacterial flagella - Campylobacter are flagellated, and their motility is important to their ability to colonise surfaces, including the intestine.

“Many bacteria produce extracellular polysaccharides that promote adhesion to surfaces - the cells have to produce polysaccharides before they leave the body, to be effective.”

Social and dependent on others

In a recent review paper - ‘Campylobacter and Biofilms’ - Dykes and Amy Huei Teen Teh, from Monash University’s Malaysian campus, reviewed research into the microbe’s ability to form biofilms.

They say that while some studies have shown that C. jejuni does form single-species biofilms on abiotic surfaces in the laboratory, not all strains do so, and some of the biofilms are in the form of aggregated cells, pellicles or flocs that are unlikely to occur on food-processing surfaces in poultry processing plants.

Moreover, most studies have been conducted under static conditions at very low oxygen levels, which do not represent real-world conditions in poultry processing plants.

The few studies made of the microbes under flow conditions have failed to demonstrate that it can form monospecific biofilms under such conditions, and pre-formed monospecific biofilms do not persist at higher flow rates.

Dykes and Teh suggest the fragility of monospecific biofilms of C. jejuni means they are unlikely to be present in poultry plants, where the atmosphere is aerobic and the cells are exposed to high shear forces.

The persistence of the species through the poultry processing chain may thus rest on the species’ ability to form mixed biofilms with other species in the processing environment - studies have shown that such mixed-species biofilms can persist under higher flow conditions than monospecific biofilms of C. jejuni.

They concluded that it is important to understand the mechanisms that contribute to the formation of complex biofilms containing C. jejuni under real-world conditions in processing plants - particularly its interactions with other biofilm-forming species.

Polymer-coated surfaces

As for the prospects of developing surface treatments that would prevent C. jejuni attaching to surfaces, Dykes says the microbe does not attach to certain polymers, but it is not yet known why - again, surface charges and hydrophobicity are likely to be involved.

There are various options for creating polymer coatings that may deter bacteria from attaching to surfaces, including ion implantation to create a negative surface charge, chemical coatings and chemical grafts, but none of these has been specifically tested against Campylobacter.

Treatments that modify surface charge are potentially complicated: compared with negatively charged materials, positively charged materials may encourage the attachment of some bacteria, while inhibiting the growth of attached gram-negative bacterial cells like C. jejuni.

Other surface coatings, including antimicrobial agents, photocatalytically active metal compounds and surfactants, have been proposed as potential treatments to reduce the risk of Campylobacter food poisoning.

Emergence of antibiotic resistance

Dykes says there is considerable strain variation in C. jejuni around the world, and virulence ranges from “mild to nasty”.

While health authorities are less concerned about Campylobacter than Salmonella and shigatoxin-producing enteric species such as E. coli strain OH7:157, there is growing concern about the ability of some Campylobacter strains to produce neurological symptoms in food-poisoning victims.

“Neurological symptoms are usually short-lived, but can be quite debilitating,” Dykes said.

Inevitably, antibiotic treatments have led to the emergence of multiresistant strains.

“With colleagues from the CSIRO, Malaysia and Poland, we recently compared isolates from each country - multidrug-resistant strains are still at fairly low levels in Australia and Poland, but they are very common in Malaysia,” said Dykes.

“Resistance is increasing, and in countries where food safety regulations are less stringent, multidrug resistance is rife - and it’s actually quite difficult to get data on which antibiotics they are using.”

Professor Gary Dykes is Professor of Food Science and Technology with Monash Unviersity’s School of Chemistry in Melbourne.  He is a former science manager of microbiology at the CSIRO’s Food Sciences Australia laboratory in Brisbane. He obtained a PhD in food microbiology from the University of the Witwatersrand in South Africa and subsequently worked in various research-based roles around the world including the Department of Genetics at the University of Natal in South Africa, The Meat Industry Research Institute of New Zealand and the Saskatchewan Food Product Innovation Program at the University of Saskatchewan in Canada.