What is Listeriosis?

Listeriosis, the illness caused by Listeria monocytogenes, can manifest with symptoms ranging from mild to severe, depending on the individual’s state of health. For healthy individuals, symptoms may be mild and flu-like, including fever, muscle aches, headache, nausea, vomiting, and diarrhoea. However, for certain vulnerable groups, the infection can become invasive, spreading beyond the gastrointestinal tract and leading to severe complications, including meningitis, sepsis, and even death.

What Are the Characteristics of Listeria?

Listeria monocytogenes possesses characteristics enabling its persistence and growth in various environments, including food processing facilities. This bacterium can thrive in cold temperatures, distinguishing it from many other foodborne pathogens inhibited by refrigeration. It can grow at temperatures as low as 0°C to 4°C, typical for refrigerated foods, meaning it can multiply even when foods are stored in a refrigerator.

Listeria tolerates salty and acidic environments

Listeria monocytogenes also tolerates salt and acidic conditions. It can grow in environments with salt concentrations up to 10% and has shown resistance to saturated salt solutions. The bacterium can also adapt to significant changes in pH, reproducing at pH values ranging from approximately 4.39 to 9.4. This acid tolerance can be enhanced by prior exposure to mildly acidic conditions, allowing it to survive the acidic environment of the human stomach. A factor contributing to its persistence in food processing environments is its ability to form biofilms. These protective structures allow Listeria to adhere to surfaces, making them more resistant to cleaning agents and disinfectants compared to free floating bacteria.

How Does it Get Into a Food Processing
Facility?

Listeria monocytogenes can enter food processing facilities through multiple routes. Raw materials, such as fruits, vegetables, and animal products, can introduce the bacterium into the plant. The natural ubiquity of Listeria in soil, water, and animal faeces means it can be carried into facilities on footwear, vehicle tyres, and equipment. Once inside a food plant, Listeria can establish itself in various environmental niches. These harbourage sites include floor drains, cracked tiles, hollow rollers, and other areas where moisture and organic matter can accumulate. The formation of biofilms in these locations is problematic, as these structures protect the bacteria from cleaning and sanitisation efforts, allowing them to persist and continuously shed cells. Cross-contamination from these environmental niches to food products is a primary concern. This can occur directly through contact with contaminated surfaces, equipment, or personnel. For instance, if a slicer becomes contaminated, it can transfer Listeria to many products it processes. Air currents, water droplets, and the movement of equipment and personnel can also facilitate the spread of the bacterium throughout the facility, especially to ready-to-eat product areas.

Source: https://biologyinsights.com/