Improving food safety practices and better understanding the risks of Listeria are vital if the fresh produce industry is to prevent future fatalities and avoid costly product recalls or marketing halts.
The 2018 Fresh Produce Safety Conference Food Safety – It’s Your Responsibility in October highlighted the prevalence of Listeria in the environment, the lack of understanding about sources and risk of infection and the lengthy testing processes as all posing key issues for the fresh produce industry.
Dr Craig Shadbolt from the NSW Department of Primary Industries said the fresh produce industry was less mature and was more complacent than other sectors in food safety awareness.
He said fresh produce would be increasingly implicated as a source of illness and significant learnings were needed to improve risk management.
“There is a low level of understanding of the sources and risks of Listeria, a poor understanding of washing and sanitising, monitoring of chemical sanitiser concentrations is lacking and there are problems with dust and hygiene in the packhouse environment,” he said.
Mixing fungicide and chemical sanitiser, Dr Shadbolt said, has the potential of one cancelling out the other.
Dr Shadbolt said investigation into the 2018 rockmelon Listeria outbreak found that the packing house in the Griffith was hygienic and well run and had had no obvious break down in hygiene. Heavy rain and dust storms boosting the bacterial load before harvest and compromising the effectiveness of washing systems, may have been responsible.
He said that while listeriosis was a notifiable disease, its long incubation (typically two to four weeks but up to 70 days) had previously made it very difficult to identify the food or environmental source.
This may be one of the key reasons listeriosis outbreaks in Australia have not – with the exception of rockmelons –been linked to fresh produce.
However, the use of whole genome sequencing, which can provide very good linkage, had been a game-changer in outbreak surveillance and traceback to source farm or packhouse.
Like DNA fingerprinting, whole genome sequencing produces such a very specific level of detail that a match between a sample from a patient with listeriosis and a sample from a packhouse environment can with a very high degree of confidence be said to be the same?/connected. The implication of this is that listeriosis can now be reliably traced back to source.
‘The fresh produce industry needs to learn from past outbreaks to instil and adopt improved food safety practices to prevent future fatalities from listeriosis,’ Dr Shadbolt said.
Microbiologist Dr Robert Premier said that although only two of the 17 species of Listeria are implicated in human infections the industry needed to better understand the potential for growth in all horticultural product lines.
“Listeria is an enigma,” he said. “L. monocytogenes is everywhere. It can spread in many ways. It grows in silage, cattle eat it, they shed it in their faeces, it dries up and blows in the wind for many kilometres. Why is listeriosis so rare?”
Dr Premier said although it was known that sheep and cattle could carry both virulent and non-virulent forms of L.monocytogenes, it was not known what triggered the shedding of virulent L. monocytogenes in animals or whether non virulent L. mono could ‘switch’ to virulent after ingestion.
Fresh Produce Safety Centre Director Dr Robyn McConchie, also Director of the Australian Research Council (ARC) Centre for Food Safety, highlighted recent research from the US showing showing.
The ARC Training Centre for Food Safety in the Fresh Produce Industry at Sydney University has a number of current R&D projects including investigating the interaction of sanitisers and fungicides in post-harvest mould control and risk assessment in apples.
- Listeria monocytogenes is widespread in the environment
- Continuous monitoring of sanitisation levels is important
- Mixing chemical fungicides and sanitisers can lead to one cancelling out the other
- Whole-genome sequencing is a game-changer in tracing back detections to source