Drosinos, who has just published a review on the prevalence and sources of cheese contamination in the journal Food Control, said the main sources of L. monocytogenes contamination are raw materials, processing equipment and environment, and the handling and hygiene practices of workers.
Focusing on the contamination risks at the processing level, the Associate Professor at Agricultural University of Athens said surveys have found that processing equipment like holding tanks, storage coolers, table tops, and conveyor systems are all vulnerable to contamination as well as environmental sites such as drains, floors, and storage areas.
L. monocytogenes can form biofilms and be spread from processing equipment and sites to end products through the ventilation system, from dripping and splashing when cleaning with high powered hoses, and by workers themselves. Indeed Drosinos said: “Poor personal hygiene has been identified as one of the most common human errors leading to illness outbreaks.”
When it comes to controlling and preventing contamination, Drosinos identified the key strategies and procedures to follow.
Prevention steps
Regarding prevention, the food science and technology expert said: “Good manufacturing practices (GMP) and good hygiene practices (GHP) should form the basis of the measures that have to be taken in order to prevent contamination of cheese and in general food products from pathogens.”
Employees should be well trained to understand food safety risks and implement good hygiene practices such as regular hand washing and use of gloves and utensils instead of bare hands. Good cleaning and disinfection routines, especially on surfaces in contact with end products, will also help minimise risk.
Another important factor is plant layout and design. Drosinos said this is because L. monocytogenes can adhere to a wide range of materials and can establish persistent contamination niches in food processing areas.
Drosinos said: “In order to prevent colonization of the processing environment by L. monocytogenes, plant layout and equipment should be designed to be more hygienic, such as without edges, crevices and dead spaces to facilitate good working routines and to ensure an effective sanitation process.”
To tackle the persistence of L. monocytogenes in food production areas it is also helpful to use materials less favourable to bacterial adherence and apply sanitisers capable of lowering the adhesive strength of the pathogen.
Control strategies
As well as thinking about prevention strategies, food companies must also consider control of L. monocytogenes contamination. Pasteurisation is one of the most obvious strategies as this destroys all bacterial pathogens common in raw milk but it is not an option open to makers of un-pasteurised cheese.
But there are other strategies open to cheese makers. Drosinos said: “The combined effect of the low water activity, the low pH and the competition with the starter culture constitutes hurdles that prevent the survival and growth L. monocytogenes in fermented dairy products such as cheeses.”
As abusive storage conditions may lead to high contamination levels, Drosinos said temperature control also plays an important role in the incidence, concentration and transmission of L. monocytogenes.
Considering that in the case of L. monocytogenes concentration levels are a crucial factor in determining whether the pathogen will cause infection, temperature control can be really important in preventing major listerioisis outbreaks from occurring.
To read more about the factors that Prolactal suspects of causing the L. monocytogenes contamination of its cheese, click here. And to read the review in Food Control Athens on cheese contamination at farm and processing levels by Drosinos and the associate professor’s colleagues at the Agriculture University, click here.