Health Aspects
Food-borne diseases associated with bacterial biofilms on food ingredients or factory equipment happen as a result of direct infection (food poisoning) or by intoxication from the compounds that microbes produce (their biproducts). For example, toxins secreted by biofilms within food processing plants can contaminate food products, causing individual or multiple intoxications. In either case, the presence of biofilms in a food factory puts human health at risk. The degree of risk is dependent on the different types of bacteria actually present within the biofilm.
Where biofilms develop depends on the factory type, but can include water, milk and other liquid pipelines, pasteuriser plates, reverse osmosis membranes, tables, employee gloves, animal carcasses, contact surfaces, storage silos for raw materials and additives, dispensing tubing and packing material.
The following are the four most important food-borne bacterial pathogens:
Bacillus cereus is commonly found in dairy factories and in food and beverage plants. It is a spore-forming bacterium that have the ability to grow over in different environments and in a wide range of temperatures (4–50°C) besides being resistant to heat, chemical treatments and radiation. This bacterium is also able to survive industrial pasteurization processes due to the production of endospores. This fact complicates the removal of its biofilm with cleaning procedures and can affect biofilm persistence in dairy factories, reducing pasteurized milk and cream shelf-life. Bacillus cereus biofilms are also associated with other microorganisms along food processing lines as it creates a more suitable surface for them to attach to.
Some strains of this bacterium cause diarrhoea and abdominal pain, while other strains cause vomiting symptoms. All of them are known to cause food poisoning.
The importance of this pathogen is highlighted by the fact that between 2007 and 2014, 6,657 persons were reported to suffer food-borne intoxications due to B. cereus in the EU (505 of them just in 2014), associated to 413 outbreaks. The foods involved in these outbreaks were buffet meals (27.6%) cereal products (10.9%), red meat products (8%), poultry meat products (5.3%) and vegetables or juices (4.6%).
Listeria monocytogenes is a dangerous, foodborne pathogen which is not resistant to pasteurisation treatments. Some examples of food products known to transmit this pathogen are seafood, dairy products, meat, ready-to-eat products, fruits, soft cheeses, ice cream, unpasteurized milk, candied apples, frozen vegetables, and poultry. Listeria monocytogenes biofilms can grow on polypropylene, steel, rubber or glass surfaces throughout the industry. From there, it spreads to food batches, where it can replicate at refrigeration temperatures. The eradication of this pathogen in the food industry is further complicated by its resistance to treatments up to 60°C.
This pathogen causes gastroenteritis in healthy individuals. In pregnant women, infants, the elderly and immunocompromised individuals, this bacterium causes listeriosis, a critical disease which also involves septicemia and meningitis.
In 2016, 2,536 confirmed human cases of listeriosis were reported, showing an increase since 2012 (1,720 confirmed human cases). Despite only five reported outbreaks due to this pathogen in 2016, it has been linked with the highest proportion (8.0%) of deaths among illness in that year. In a similar way, four listeriosis outbreaks, spanning from 2014 through 2016, have been linked to L. monocytogenes strains.
Salmonella enterica causes gastroenteritis or septicemia. It can generate nausea, vomiting, fever, diarrhoea and abdominal pain as main symptoms. In the case of systemic infections, fatalities can reach up to 20% of the affected patients during an outbreak, especially children and immunocompromised individuals.
Poultry meat is a common reservoir for these bacteria in processed food. Its importance as a food pathogen is demonstrated by the fact that S. enterica biofilm formation on food surfaces was the first reported of these complex, multicellular structures. S. enterica is able to grow on stainless steel surfaces, resulting in a 3D structure with several layers of cells, which may present different morphologies depending on the available nutrients. Of particular importance is that under dry conditions S. enterica can survive in a biofilm on stainless steel for over a year. From there, it is possible for this bacterium to contaminate thousands of food batches.
Salmonella enterica is capable of attaching to meat and other food matrixes easily, eventually leading to cross-contamination between food batches in a manufacturing plant or supermarket, a fact that further underscores the serious health concern this bacterium poses with respect to outbreaks risk.
The main source of contamination by this bacterium is biofilm formation in infrastructures used during pre-cooked foods manufacturing (such as pre-cooked chicken).
In 2016, S. enterica was identified as the second most frequently agent (just after Campylobacter) of food-borne and water-borne outbreaks in the EU, with 94,625 cases. This bacteria accounted that year for 12,353 hospitalizations and 126 deaths (50% of all deaths associated to outbreaks). These numbers show a reduction with respect to previous decade, mainly due to more strict control and detection measures at production factories and distribution chains.
Staphylococcus aureus is able to multiply on the mucous membranes and skin of food handlers, a major issue for food factories.
Food products with high sugar or salt content are great as a food source for this bacterium.
Staphylococcus aureus is a human opportunistic pathogen which produces enterotoxins at temperatures between 10 and 46°C. These enterotoxins lead to acute toxic shock with diarrhoea and vomiting. Moreover, the emergence of methicillin-resistant S. aureus (MRSA) in farm animals has caused great concern because this bacterium is able to form biofilms on many different kinds of animal surfaces.
Staphylococcus aureuscan form biofilms on both living and non-living surfaces along the food production chain. The removal treatment is different depending on what material the surface is made of. Some options are; glycoside hydrolases (such as Dispersin B, produced by Aggregatibacter actinomycetemcomitans) and proteases (such as proteinase K, a serine protease from the fungus Engyodontium album). The growth of S. aureusbiofilms is enhanced by various processing methods encountered in the food industry, such as suboptimal temperatures, improper disinfection or a combination of salt and glucose.
In 2015, 434 outbreaks were caused by this bacterium in the EU. In 2016, in the United States, 241,994 cases of this type of food poisoning were reported, with 1,067 hospitalisations and 6 deaths.
Further reading on health aspects of biofilms in food factories
Galié Serena, García-Gutiérrez Coral, Miguélez Elisa M., Villar Claudio J., Lombó Felipe. Biofilms in the Food Industry: Health Aspects and Control Methods. Frontiers in Microbiology, Vol 9, 2018, pp898. https://doi.org/10.3389/fmicb.2018.00898
This page is still under development. Can you help us to complete this page? Please contact us.