Listeria monocytogenes is a gram-positive bacterium that can cause a serious infection known as listeriosis, primarily affecting individuals with weakened immune systems, pregnant women, newborns, and the elderly. The bacterium is commonly found in food products, making contamination a significant concern in the food industry. Outbreaks of listeriosis generally arise from contaminated dairy products, meats, and vegetables. Since this organism is capable of surviving under low-temperature conditions, Listeria can grow even under refrigerated conditions. Product testing for Listeria monocytogenes contamination is thus important to ensure product safety and build compliance with global food safety standards.
The importance of testing for Listeria monocytogenes contamination
Product testing for Listeria monocytogenes is not only imperative for preventing outbreaks but also plays an important role in public health safety. Food manufacturers are under stringent regulatory compliance, such as the Food Safety Modernization Act (FSMA) from the FDA in the United States and guidelines on food safety policy of the European Union. Contamination of products with Listeria will result in costly recalls, brand name damage, and possible legal action in worst cases. Thus, a stringent product testing for Listeria regime enables food manufacturers to adhere to safety standards while ensuring the protection of consumers.
Types of food products susceptible to Listeria contamination
Listeria monocytogenes can be found in a variety of food products, most commonly those that are ready-to-eat (RTE), as they bypass heat treatment or other decontamination processes during manufacturing. Key high-risk foods that need product testing for Listeria include:
- Dairy Products: Soft cheeses, raw milk, and unpasteurized dairy products are prone to Listeria contamination.
- Meat and Poultry: Deli meats, cold cuts, and hot dogs, which are often consumed without further cooking, are susceptible.
- Seafood: Smoked fish and shellfish can harbor Listeria if proper handling and processing protocols are not followed.
- Vegetables: Raw, pre-packaged salads and vegetables, particularly those washed in contaminated water, are at risk.
- Food industries undertake product testing for Listeria to find and eliminate the contamination before it reaches the consumers.
Key methods
ISO 20743: Antibacterial Activity of Textile Products
ISO 20743 provides details methods about textile product testing using Listeria for the antibacterial activity. The standards are important in industries where hygiene plays a major role for example, in textile products to be used in medical or sports equipment.
Testing Methodologies:
- Absorption Method: Inoculation of the textile sample with bacterial suspension is the first step, followed by incubation in controlled conditions. Bacterial recovery is done after a specified period, giving the degree of bacterial reduction on the textile. It is applied to only those textiles that can absorb bacterial suspension.
- Transfer Method: The bacteria is introduced onto the surface and then the textile sample is placed on it. After incubation, bacterial growth is observed and compared with the control sample to get the efficacy of the textile against the bacteria.
- Challenge Bacteria: The standard typically uses Staphylococcus aureus and Escherichia coli for determining the antibacterial properties of the textile.
The test results are based on bacterial count reduced compared to an untreated control. This method of testing. It has helped find out the antibacterial finishes applied to textile materials.
2. ISO 22196: Antibacterial efficacy on plastic and non-porous surfaces
The antimicrobial activity of plastic surfaces or other non-porous surfaces can be determined by ISO 22196. This standard is often applied in industries that manufacture antibacterial plastics for product testing for Listeria, which are used in the manufacturing of medical devices, household goods, and packaging materials.
Testing process:
- A bacterial suspension (usually Staphylococcus aureus or Escherichia coli) is applied to the surface of the plastic material.
- The sample is then incubated under specific conditions to allow bacterial growth.
- After a specified period, the bacteria are recovered from the plastic surface, and the bacterial reduction is calculated by comparing the treated sample with an untreated control.
ISO 22196 becomes imperative on products so as to prevent the growth of bacteria on their surface, hence providing long-term protection with reduced contamination risks.
3. EN 13697: Surface disinfection testing for non-porous surfaces
EN 13697 is the European Standard which deals with methods for the bactericidal and fungicidal activity testing of chemical disinfectant product testing for Listeria on non-porous surfaces. Food processing industries, healthcare and pharmaceutical industries are most concerned about this standard as it covers disinfection of surfaces in order to prevent contaminated conditions.
Testing procedure:
- A bacterial or fungal suspension is inoculated onto a non-porous surface, usually of stainless steel or plastic, commonly Staphylococcus aureus, Escherichia coli, Pseudomonas aeruginosa, or Candida albicans.
- The disinfectant will be applied to the contaminated surface for a predefined contact time that allows microorganisms to be in contact with the disinfectant.
- The disinfectant is neutralized to stop the contact time, and the remaining viable microbes are recovered.
- This would involve evaluation of the bactericidal or fungicidal action of the disinfectant through comparison of the surviving microorganisms’ count on the test surface with that from a control sample.
4. ISO 16140: Validation of methods for detection of foodborne pathogens
ISO 16140-2 provides a comprehensive standard for the validation of methods used for product testing for Listeria in the detection of foodborne pathogens, including Listeria monocytogenes. This standard is unique because of the emphasis given to manufacturers and testing laboratories in using proper and effective methodology for detecting the pathogen and meeting global food safety regulations.
Key Steps in Validation:
- Method selection: The very first step is to decide upon the method that has to be validated, whether it is going to be some reference method or some alternative method for the detection of foodborne pathogens.
- Comparison with a reference method: It is then compared to a reference method-like ISO 11290 for detecting Listeria to identify its performance with regard to that pathogen.
- Performance characteristics: The sensitivity, specificity, accuracy, precision, and the limit of detection are gauged for the said method during the process of validation. This helps to ensure that the method will be capable of detecting small amounts of pathogens with the least possible numbers of false negatives or positives.
- Inter-laboratory comparisons: To ensure the robustness of the method after it has been tested under various conditions and in different laboratories. This will ensure that the conditions present in these different laboratories are capable of allowing consistent performance for this particular method regardless of the kind of instrument used.
- Matrix validation: This includes testing the performance of the method using different food matrices such as dairy, meats, vegetables, among others.
Effective product testing for Listeria monocytogenes contamination is an important aspect in the line of defense for food manufacturers and related industries to protect public health and ensure compliance with strict food safety regulations. With routine testing, environmental monitoring, and rapid detection methods, the manufacturer can avoid costly recalls and additional brand reputation damage.At Microbial Investigations Switzerland (MIS), we provide testing and validation services. Contact us today to learn how we can help you maintain the highest standard of safety inside your food production process.
