Staphylococcus aureus in the food industry
Bacteria commonly found in the environment, present in food industries on floors, tools and surfaces and in water and air…, they can live in humans and animals. They are one of the most resistant non-spore-forming pathogens and can survive for long periods of time in low humidity environments. They grow between 7ºC up to 47.8ºC, but the optimum development occurs at 35ºC. Regarding pH, the growth range is between 4.5 and 9.3, optimum between 7.0 and 7.5. Gram positive, immobile, catalase positive, they are impossible to eradicate from the environment.
Their ability to produce heat-resistant enterotoxins in a few hours makes them a type of bacteria that causes a large number of food poisonings. These toxins can produce nausea, diarrhoea, intense vomiting, but the duration of the symptoms is short, from several hours to a day. The toxin acts quickly, and its symptoms appear within a few hours of consuming the contaminated food.
As a general idea, their presence in food indicates lack of hygiene during the food production process, poor hygienic practices by the handlers, inadequate design of cleaning and disinfection processes or inadequate products used during these processes. On the other hand, their presence is taken for granted in the daily production processes, either by handlers, raw materials, environments…, but its easy elimination when it is in planktonic conditions with the daily C&D processes, due to its high sensitivity to adverse conditions, such as temperature, pH, chemicals, does not allow the time necessary for Staphylococcus bacteria to generate toxins.
Enterotoxins generated by Staphylococcus are simple protein chains with a molecular weight of 26,000 to 29,000 daltons. They are resistant to proteolytic enzymes, such as trypsin and pepsin, which enables them to access the human digestive tract intact. The infective dose is less than 1 microgram, produced when the concentration of the bacteria in the food exceeds 100,000 organisms per gram of food analysed. This level is an indication of poor sanitary conditions during the food preparation processes. In susceptible population, the ingestion of between 100-200 nanograms of enterotoxin can cause the first symptoms of the disease.
Stressing the aspects related to hygiene in the facilities, it is worth noting the importance of the correct planning of all the processes that will affect the overall result of the food business, both at a productive level and with regards to product quality, since failure to observe the importance in the selection of professional suppliers in each of the areas we are dealing with, may cause important losses of costs, image… often unrecoverable.
Revisiting this matter. Why is the knowledge of hygiene processes by specialists important? Why should the use of chlorinated alkali as a general disinfectant be discussed? What effects does sublethal concentrations of biocidal active substances have? How is it possible that with no positive results of Staphylococcus aureus on surfaces, tests on enterotoxins produced by them continue yielding positive results? How, where and why are Staphylococcus biofilms formed and what do we do to ensure their removal? How do biocides act on the structure of these bacteria and at what dose are they destroyed?…
All these questions must be answered when considering the development of a C&D programme in a food industry in case of a specific problem, considering that the general hygiene programme established with its operating procedures must be compatible and adaptable to sporadic appearances of results not in line with established analytical standards. Generally, the main objective of the facilities and machinery design in the food industry is food production, in many cases investing too late in hygiene.
Production processes, incoming and outgoing auxiliary materials, raw materials, air currents, flows of personnel, machinery…, are necessarily detrimental to the facilities’ “sterility”. Food industries are living ecosystems, the internal survival struggles of all living beings that conform the industry biocenosis, adaptations, mutations, resistances, biofilms, quorum sensing, self-inductors… appear on a daily basis. For this reason, it is important to be aware that the absolute zero is impossible and it would also be counterproductive. Microorganisms in general, and bacteria in particular, have been on Earth for millions of years, have adapted and have been able to resist incredible evolutionary processes. Therefore, if we bring these two factors together, we must know the importance of doing very well the little we can do. By making a metagenomic analysis of food processing plants, overcoming the need to isolate and cultivate the individual species in the laboratory, we will discover the great variety of microorganisms’ communities in their natural environments present in any industry where work is undertaken.
The staphylococcus toxin in food, in a company that adequately fulfils its cleaning and disinfection procedures according to its hygiene service provider, is a clear indicator of poor service. Either the products are not suitable (it can happen when the recommendation is “one single pass”, usually with chlorinated alkaline), or there are signs of biofilm with Staphylococcus not detected (dispersion of the biofilm in damp environments with aerosols), or the thermal processes that destroy bacteria, not toxins, do not work properly.
Considering a biofilm as a biologically active matrix formed by cells of one or several species and extracellular substances in association with a solid surface, we must bear in mind that under suitable conditions, it will release fragments that may appear sporadically in the food. The existing synergies within the biofilm’s community are the factor that enables bacteria to withstand adverse conditions and survive.
The matrix of these biofilms protects the microorganisms against antimicrobial agents, prevents access to biocides, metal sequestrants, toxins, prevents dehydration, reinforcing the resistance of the biofilm to environmental stress, allowing microorganisms to capture nutrients. The requirements for the biofilm’s development are the presence of microorganisms and substrate. If any of these is not available, the biofilm will not be formed.
Nutrients, limiting water, equipment design and temperature control are important aspects in biofilm control, but these variables are difficult to change, so the biofilm’s control is reduced to the effectiveness of cleaning and disinfection on areas and process equipment. Cleaning is done using chemicals and a combination of physical and chemical effects. Chemical cleaning agents suspend and dissolve food residues by reducing surface tension, fat emulsification and proteins peptization, as well as dissolving the biofilms matrix, following the visualization with specific stains (catalase/false negative tests are not recommended).
In most food processing plants, food contact surfaces are cleaned and disinfected on a daily basis. Nevertheless, many other surfaces such as storage deposits and the outside of the pumps, an effective cleaning plan is not followed on walls and ceilings. These generates an opportunity for biofilms to develop thanks to moisture. On the other hand, the formation of aerosols is one of the main sources of microorganisms’ dispersion. They occur while washing surfaces and drains, or when biofilms dry and release particulate material. It was demonstrated that pathogens such as S. aureus remain viable on steel surfaces, even when dry, after performing C&D processes. The idea of quickly drying stainless steel surfaces after the cleaning and disinfection process could reduce the proliferation of bacteria, since water is a factor that enhances microbial growth and biofilms formation. Several studies undertaken in this regard, and legislation in some non-EU countries, stress the convenience of drying the surfaces, but with a prior analysis of the air that will be used in the drying process (in one of the tests performed, environmental Listeria spp. appeared on the surfaces to be dried).
