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.