New defences against food poisoning

Of all the biohazard notices outside microbiology labs at the Tasmanian Institute of Agriculture (TIA), most prominent are the signs warning that Listeria bacteria are used inside for research.

Listeria monocytogenes is a bacterium found naturally in soil, vegetation, water, animals, our own bodies – and as a result, on our food.  

“It’s tenacious, hard to kill, and lives everywhere”, said Associate Professor John Bowman, leader of the Centre for Food Safety and Innovation at TIA.

“Unusually, it survives freezing temperatures, which means that Listeria can continue to grow in refrigerated foods that are contaminated,” he said.

In the prestigious journal ‘Frontiers in Microbiology’, TIA and CSIRO Agriculture and Food have just jointly published a review of novel methods to control Listeria in food production facilities.

The microbe can cause a rare but serious food-borne disease called listeriosis, especially among pregnant women, their unborn babies, the sick, and the elderly.

Listeria is more likely to cause death than other bacteria that cause food poisoning, like Salmonella, Campylobacter, and E.coli,” Assoc Prof Bowman said.

“In fact, around 30 percent of food-borne listeriosis infections in high-risk individuals are fatal.”

He said that while hygiene standards are high in Tasmania, chilled foods like salmon, salad leaves, soft cheeses and dairy products can be particularly prone to Listeria.

“It’s important for Tasmania, because we’re well known for making these premium high-value chilled food products that spend some time in the fridge. This can make Listeria control and surveillance a bit more complicated,” he said.

Lead author of the review, Dr Jessica Gray from CSIRO Agriculture and Food, said that food manufacturers face an ongoing challenge to prevent the entry of Listeria to their production facilities, especially if equipment is worn or poorly designed.

Listeria is a difficult organism to eradicate and its presence still occurs even with the best sanitation plans and manufacturing practices,” she said.

“The Listeria bug is hard to remove with traditional cleaning and disinfecting procedures because of the way it grows in resistant colonies called biofilms that are tolerant of antimicrobial treatments.”

The CSIRO-TIA team looked at the potential of using new biological control methods against Listeria in food production facilities, to decrease cross-contamination and prevent spoilage of food.

These methods include the application of essential oils like clove and spearmint; using ‘good’ bacteria to out-compete the ‘bad’ Listeria; and introducing viruses that infect and kill bacteria, called bacteriophages.

“As consumers become more conscious of food safety significance, and science learns more about how crucial biofilms are to the survival of Listeria, interest in novel biocontrol methods is growing,” Dr Gray said.

Their review found that the use of competitive bacterial species shows promising results, and some bacteriophages are now used commercially. Because essential oils affect taste, particularly at the concentrations needed to be anti-microbial, they are best used as an extra safeguard for non-food contact surfaces.

Assoc Prof Bowman said there is plenty of scope to ‘think outside the box’ when seeking new and more effective ways to increase food safety, and knows the Tasmanian food industry is keen to find them.

“When food products contaminated by bacteria have to be recalled, the cost to industry is high in terms of economic burden and brand damage,” he said.

The cost of Listeria contamination to human health and safety – where a dirty meat slicer could kill dozens of people – is even higher. The largest listeriosis outbreak in history continues in South Africa, with more than 1000 cases and 200 deaths (including 80 babies), traced to processed meat products.

Earlier this year in Australia, Listeria-contaminated rockmelons infected 17 people and killed five.

TIA’s microbiology team at the Centre for Food Safety and Innovation provide industry and government with access to cutting-edge research and knowledge of emerging issues related to food safety, shelf life, and innovations in food quality and processing.

This article appeared in Tasmanian Country on 11 May 2018.

Published on: 11 May 2018 9:18am