Listeria: How to win the war that never ends

Risk. It’s an inescapable part of life that’s always around us, invisible … until it’s not. In the food industry, safety risks, such as listeriosis – a pathogenic bacterial infection – can threaten the strongest of brands, people’s health and even their lives.

According to Food Standards Australia New Zealand, each year in Australia around 150 people are hospitalised with listeriosis and about 15 people die. Recent tragedy provides another reminder that the war against human pathogens goes on and on. Although the rate is declining, Australia has seen eight Listeria-related product recalls in the past 18 months.

The tactical warfare waged by the global food industry against food safety threats is multifaceted and grows increasingly sophisticated. Manufacturing facilities take ever-greater measures to ensure that equipment is as sterile as possible and pathogens don’t enter the processing stream. Molecular diagnostic pathogen test kits are getting shorter time to results. Packaging solutions such as antimicrobial sachets, films, coatings and high-pressure processing (HPP) also contribute to the cause. Foods are formulated to include antimicrobial ingredients that inhibit microbial outgrowth.

Food safety is complicated
“It’s difficult for manufacturers to know when the safety measures they’ve taken are truly sufficient,” said Andrew Pearce, ANZ country manager at Corbion, an ingredient solutions provider known for its expertise in food preservation. “When hygienic practices and ingredient solutions are in place, and no problems are detected, it’s easy to believe that there are no problems.”

Corbion works with food manufacturers to implement high-performance safety and shelf life solutions in a wide variety of applications, including bakery, meat, culinary, confectionery, dairy and beverage products. Although the company has been honing its expertise in this area for 80+ years, Pearce said finding the best solution to a given customer’s challenge is never a simple matter.

“Food safety may start with minimizing the microbial load in the raw materials and equipment used to process a food product,” Pearce said, “but then it comes down to the conditions in the product itself and whether those conditions support or inhibit the growth of pathogenic bacteria. It’s next to impossible to create a perfectly sterile product, so making sure you make it difficult for unwanted microbes to grow is crucial in food safety.”

The composition of the product is everything, Pearce explained. It’s not just that the right solution for a salad dressing is different than it is for a deli ham product; the best answer for a cured deli ham may be quite different from what’s needed in uncured deli shredded chicken. Protein and water quality, sodium content, and other ingredients all impact the chemistry of the food matrix. The lower the pH (i.e., higher acidity), the less hospitable the product is toward microorganisms. If the product’s storage temperature isn’t low enough, bacteria are better able to grow.

Listeria monocytogenes is a major concern for food regulators and manufacturers in part because it can grow even at refrigerated temperatures and in products with low water activity. While Listeria is inactivated at cooking temperatures, it can often re-enter the food supply following heat treatment.

Rising to the reformulation challenge
Adding another level of complexity to the challenge for manufacturers is the fact that incorporating a food safety solution has the potential to wreak havoc with important aspects of product quality and sensory appeal – things like flavor, texture, and shelf stability.

Thinking about what it takes to make consumers happy, in addition to keeping them safe, can also put limits on the kinds of ingredient solutions that can be considered. An increasing number of consumers check ingredient labels before purchasing foods in an effort to avoid ingredients they don’t understand or aren’t comfortable with. This challenges manufacturers to deliver the same product attributes (including safety) using more “natural” solutions they may never have worked with before.

“Reformulating food products is a complex undertaking because every part of a food matrix is connected to every other part,” Pearce said. “It takes an in-depth understanding of those interdependencies to be able to change one component of a formulation without losing important product characteristics.”

The process of reformulation is iterative, involving a sometimes lengthy series of sensory and microbial tests, each including small changes in dosages, ingredient composition and other factors. Corbion uses a combination of experience and advanced, data-driven modeling tools to quickly identify the optimal solution that meets the manufacturer’s food safety requirements while preserving the attributes of product quality that are so important to creating success in the marketplace. The Corbion Listeria Control Model, for one, leverages data from more than a decade of clinical studies, internal challenge studies, and external validation studies in real food matrices  to estimate the effectiveness of various pathogen control solutions, considering moisture level, pH, water activity, and levels of sodium, potassium and nitrite.

The right ally can make the difference
For food manufacturers, a dedication to achieving hygienic conditions within their own facilities and supply chains is an important part of what it takes to create foods that begin the journey to the consumer as microbiologically safe. But maintaining non-pathogenic integrity throughout that journey – including the product’s lifespan on the customer’s shelf – requires a level of know-how that can’t be taken for granted, even among ingredient suppliers, according to Pearce.

Having access to outside ingredient knowledge and microbiological expertise to complement in-house strengths can speed product development, result in a superior end product and dramatically reduce food safety risks that could threaten the public and the manufacturer’s brand. Choosing the right partner can improve outcomes by combining strengths in innovation, formulation, modeling, manufacturing, quality testing, market insights and other industry best practices.

Since producers prioritize their product safety programs, the outlook is good, Pearce said. “The food industry will never be able to stop fighting against Listeria and other pathogens, but with the help of food safety experts and state-of-the-art ingredient solutions, manufacturers – and consumers – can keep winning.”

Good manufacturing practice key to reducing listeria risk

Between 2005 and 2014 more than 586 product recalls were initiated by Food Standards Australia New Zealand (FSANZ), with 198 due to Listeria Monocytogenes contamination, writes Bonnie Tai. 

With meat and dairy more susceptible to contracting the potentially-lethal pathogen than any other food product, FSANZ spokesman Raphael May told Food Magazine that it’s important that plant managers and staff gain a good understanding around the risks associated with Listeria. 
“Basic principles for controlling listeria in food include equipment and facilities that should be designed, constructed and laid out to ensure clean-ability, minimisation of harbourage sites and prevention of cross-contamination,” he says. 
“They should also be controlled to minimise the growth of Listeria Monocytogenes in the finished product, and to reduce the likelihood that the product will be re-contaminated or will support the growth of Listeria during subsequent distribution, marketing and home use.”

Although Listeria has been known for at least 60 years, it has only been linked to foodborne disease since the early 1980s. Since then, the pathogen has become recognised as an important food poisoning bacterium. 
While healthy individuals can become infected with Listeria, the most at-risk are the elderly, the young, pregnant women, and those with a compromised immune system. 

Despite the fact that there are a number of other pathogens that affect the food manufacturing industry, Listeria is perhaps one of the most dangerous. 
This is because the foodborne bacterium – when present in food – shows no difference in taste, smell or appearance; leading people into a false sense of security that the contaminated item is, in fact, safe to eat. 

With its unique ability to thrive and survive in even refrigerated conditions, ranging from below 1°c up to 44°c, Listeria is an organism that can fast become a lethal liability for food manufacturing industries if floor-staff are not properly educated on the dangers of an outbreak. 
So far there have only been two major recorded outbreaks of Listeriosis in Australia, reports Meat and Livestock Australia (MLA).  Once in 1990, when six stillborns, following an autopsy, were discovered to have all been infected with the same subtype of Listeria, found in a particular brand of Pate. 

The next episode occurred in 1991, after three people who ingested the same brand of smoke mussels became violently ill. An unopened packet of mussels was subsequently tested and was found to contain 107 listeria cells per gram – despite industry-dictated ‘safe’ levels sitting at less than 10 cells per gram. 
Sporadic cases still occur in Australia, with around 40 being reported per year. The numbers overseas, however, are significantly higher and the outbreaks much more severe. 

According to the MLA, 86 to 314 cases of Listeriosis were linked to the consumption of branded Mexican-style cheese in the US, resulting in a 30 per cent mortality rate among those infected. The pathogen was later traced back to the factory, and it was discovered that raw untreated milk was added to the pasteurised cheese to enhance flavour. 

As Listeria Monocytogenes is a ubiquitous organism that is found in a wide variety of environmental niches, it can be extremely difficult to eliminate from the processing environment, explained Mr May, and instead particular emphasis should be placed on minimising the risk as much as possible. 
“Data shows the rate of notifications [of Listeriosis] has remained steady over the last 10 years,” he says.
“As it is difficult to completely eliminate the risk…communications campaigns targeted at vulnerable populations, have been developed to improve awareness.”

The steps you can take to protect your plant
Microbial contamination can severely impact a food processing plant’s brand equity, authority and reputation, so it’s vital to follow FSANZ’s two-step approach to reduce the risk of Listeria spread.  
1. Environmental Monitoring 
The food processing environment should be regularly monitored and tested for L. monocytogenes or a surrogate such as Listeria spp. This is particularly important in facilities producing ready-to-eat foods that can support the growth of listeria, and should be undertaken to verify that cleaning and sanitation programs are working and there is control of niches and harbourage sites. 
Sampling and testing methods used should be sufficient to provide confidence that the environment is under control or to help clearly identify that further follow up actions are required. 
2. Process Control
Cross lot testing of finished products should be implemented to assess the performance of food safety control systems from within the plant. This helps to verify that the production and processing controls put in place are working effectively. 

To ensure that corrective actions are being implemented before microbiological criteria is exceeded; a sample schedule should be put in place as appropriate to the operations of the food business. 


RECALL NOTICE: Cottage Cheese Farm Goats Fetta

Cottage Cheese Farm Pty Ltd has recalled Cottage Cheese Farm Goats Fetta Cheese from Cottage Cheese Farm and Middle East Bakeries in Victoria due to microbial (E.coli) contamination. Food products contaminated with E.coli may cause illness if consumed. Any consumers concerned about their health should seek medical advice and should return the products to the place of purchase for a full refund.

Date notified to FSANZ


Food type


Product name

Cottage Cheese Farm Goats Fetta Cheese

Package description and size

Plastic 2.3L tub (height – 145mm x diameter – 176mm), 1kg

Date marking

Use By 03 Jan 16, 05 Jan 16 and 06 Jan 16

Country of origin


Reason for recall

Microbial (E.coli) contamination


Cottage Cheese Farm and Middle East Bakeries in Victoria

Consumer advice

Food products contaminated with E.coli may cause illness if consumed. Any consumers concerned about their health should seek medical advice and should return the products to the place of purchase for a full refund.


Cottage Cheese Farm Pty Ltd

03 9306 2516