Listeriosis

cheese-1278812_1920Food spoilage is really nothing more than a natural deterioration of organic matter. Everything in nature has to be broken down so that it can once again become part of the composition of soil. All of the various natural processes that participate in the spoilage of organic material are ultimately directed toward this aim.

Odor. Bad odor is a symptom of food spoilage. Foods that have a bad odor should be thrown out. We have already gone into the causes of foul refrigerator odor with regards the spilage of food. Yet there is another factor that we should take into consideration when talking about foul odors of food and that is that the odors can be soaked up by foods which have not spoiled and make them disagreeable to eat. In saying that, this problem does not only pertain to food which has spoiled. Nobody would like to eat a piece of cake that has adopted the odor and taste of smoked salmon, for instance. This is a major problem in the home kitchen. Luckily there are now products available that help to reduce the severity of refrigerator odor and foul taste transfer between foods. Now you can buy a refrigerator purifier that will prove invaluable in the prevention of refrigerator odor. This product is a real food saver. Small air filters for fridges are also available.

When we define food spoilage we can say that spoilage of food pertains any disagreeable change in the nature of food from the normal condition that we expect. These changes may compromise food hygiene. We are able to distinguish these changes through use of our senses. For instance, food may change visually, it may change in smell, to the touch or in taste. In saying that, we use some forms of what technically amounts to food spoilage, in a controlled way, to achieve a desired effect, as in Camembert cheese for instance. We crave the runiness of the cheese that is produced by specially selected bacteria and mould to produce an effect which many of us find pleasing to eat. Other examples of controlled food deterioration include Danish blue, Gorgonzola, Stilton and many other forms of cheese. We also tenderize meat such as game by jugging it or purposely speed up the deterioration process of meat when we inject lactbacillus bacteria into steak to mimic the ageing process. In short and in technical terms, food spoilage works for us easily as much as it works against us.

Nevertheless, food does spoil because once the fruit of vegetable has been picked or the animal has been slaughtered, the natural processes and defences of the organism are compromised and exposure to the outside environment causes a number of inevitable changes to occur.

The factors which bring about these changes include, air and oxygen, light, moisture, microbial growth factors and ambient temperature. Some of these changes indicate poor food hygiene and cross contamination and others point to chemical reactions and changes due to physical phenomina. Let’s go through the various causes.

Air and oxygen: Air comprises of about eighty percent nitrogen and about twenty percent oxygen. The level of oxygen in the air is too great for most organisms and therefore organisms have developed strategies to counter the harmful effects of oxygen. Our lungs are lined with a substance called surfactant. Surfactant provides a necessary barrier between the tissue of the lung and the oxygen in the air to counteract the caustic effect of the oxygen upon the lung tissue. Our bodies and the bodies of other organisms produce anti oxidants to counter other undesirable reactions of oxygen with substances called free radicals. By binding to free radicals, anti oxidants prevent reactions which are harmful to our bodies. When an organisms no longer has the support of it’s various physiological support systems, the chemical make up of the organism will start to react with the oxygen in the air.

Micro organisms which require the presence of oxygen in order to metabolize organic tissue, such as aerobic bacteria and moulds, are able to colonize those areas of the flesh which are exposed to the air. The will form colonies upon the food and start to metabolize the flesh of the organism and divide at a rate of one division every twenty minutes per bacterial cell. In some cases as few as one thousand bacteria can be enough to contitute a food hygiene risk.

Enzymes, particularly oxidizing enzymes, which react with oxygen also aid the process of food spoilage. In vegetables enzymes such as catase and peroxidase cause the familiar browning of the flesh of foods such as apples and potatoes. Enzymes are substances which speed up chemical reactions and enzymatic reaction with oxygen in organic matter causes the degeneration of the matter to hasten considerably. In cooking a rapid heat treatment known as blanching is used to cancel these enzymatic reactions. Enzymatic changes do not usually render food inedible but if combined with microbial infestation such as mould or certain bacteria the ingestion of such spoiled food would constitute a food hygiene risk.

Water: water is the most abundant substance in nature. All organisms are made up of at least seventy percent water. The water within an organism when it is alive is termed as bound water because it is chemically connected to other substances within the body. All living organisms maintain a certain level of chemical concentration. This is said to mimic the concentration of sea water from which all living organisms originate. Concentrated fluids flow around the cells and each cell contains within it a carefully controlled liquid environment. The balance between the concentration of the fluids which flow around the cell and the fluid which exists within the cell is carefully regulated by the central control system of the organism, whether it be plant or animal. In higher organisms this process is called homeostasis.

Once a plant or an animal has been cut into smaller parts, the tissues whose fluid environment was once carefully controlled are now exposed to the environment. When the organism’s flesh comes into contact with moisture a physical phenomenon occurs. All substances in nature try to match their concentration levels to other substances around them, This is called diffusion. The flesh of an organism, when exposed to water will soak up the water in an attempt to dilute the concentration levels within the flesh of the organism to the concentration levels around it. This may cause the cells of the organism to explode by being too full of water. This form of tissue deterioration is a major cause of food spoilage. This intake of moisture into the tissue of the food source is the perfect vector for micro organisms to infest it. This is a very good example of how food spoilage occurs and food hygiene breakdowns happen.

In addition, excess “free” water within or around the cell gives bacteria the perfect medium in which to operate. In bacterial terms this is like a super highway in which bacteria are able to spread throughout the flesh of an organism. Water within an organism can be controlled by a) dehydration, b) freezing or c by the addition of food preservatives.

Light: Spoilage of food which is caused by light is called photo degeneration. All food is exposed to light at some time or another. Light can be either natural light or artificial light. Light, like all other forms of energy is made up of different wave lenghts. At the outer ends of the light spectrum we have infra red and ultra violet light which can vary in intensity in different parts of the world. These forms of light radiation are known to be harmful and can cause dead and live tissue to react in negative ways.

Exposure to light sources can cause foods to change in nature. Pigments may change, as may vitamin levels, fats and proteins. In solid foods the density of the material such as in meat may block deep penetration of light and therefore the effects of light may only cause changes to happen on the surface of the product. In liquids light penetration can be much deeper and therefore the effects of photo degeneration can be much more substantial.

Microbial growth. Micro organisms play a vital role in the balance of nature. Bacteria and other types of microbes haves each evolved to fill a specific niche. Some bacteria have developed a symbiotic relationship relationship with living organisms and some have developed a parasitical relationship. Healthy organisms manage to keep parasitical bacteria at bay through their immune systems and homeostasis. However, parasitical bacteria are constantly on the look out for signs of weakness and it is their job to bring about the rapid demise of sick organisms and to ensure that they are re cycled back into the environment through the process of tissue deterioration and degeneration. In prehistoric times man did not store much food. He ate from hand to mouth and so food did not have much time to go off. Modern man, because of his lifestyle, needs to store food and to do this he needs to effect a different kind of environmental control in comparison to prehistoric man.

In a previous chapter I mentioned that psicrophilic bacteria can cause food spoilage at low temperatures. In cold climates landscapes freeze for many months and animals find it difficult to survive. Weaker animals die during the winter months and remain frozen until the beginning of the thaw in spring. Although thawed a carcass may remain too cold for many types of bacteria to develop and it is for this reason that certain bacteria adapted to this niche so that the detioration of the carcass could begin. This process helps to ensure that the period of time during which more pathogenic bacteria infest the carcass and hence spread into the environment is considerably lessened. This is the function and importance of psicrophilic bacteria in nature. We can control the undesirable effects of psicrophilic bacteria in our cold stores through the implementation of a good hygiene regime.

In general, sources of food contamination come from the environment particularly from, animal wastes, soil, water and air. Here the “Four stages of food hygiene” come into play. Great care must be taken to make sure that food comes from safe sources, that food does not come into contact with other bacterial sources, that bacteria does not have conditions for growth and that tools and work surfaces are kept free from bacteria. food hygiene regime and temperature is all critical here. Don’t make mistakes or cut corners and bacteria will not develop.

Temperature. Temperature is probably the single most important environment which we can control to prevent the spoilage of food. Temperature regulates several changes in the nature of organic matter. Firstly it slows down chemical reactions within the food. Secondly it can prevent the ggrowth development of bacteria or destroy bacteria through cooking, Temperature regulation can control the destruction of vitamins and prevent dehydration and ripening of food.

However, temperature need to be professionally controlled. Over freezing can cause surfaces to crack of the development of ice crystals at microscopic levels can puncture cells causing the flesh to become soft and pulpy. Pigment can be lost and chemicals within the food may react and loose much of their nutritious value. This process is commonly called freezer burning.

In cold stores vegetables and fruit are best held at temperatures of around 10 degrees Celsius. meats should be chilled to four degrees Celsius and frozen food should be stored at -18 degrees Celsius for a period not exceeding six months in most cases. Aaways make sure that you follow manufacturers storage instructions. If in doubt don’t be afraid to contact the manufacturer or importer to get their advise.

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What is listeriosis?
Listeriosis is a bacterial infection caused by the bacterium Listeria monocytogenes. Until several years ago it was thought that this bacteria only infected animals but it is now accepted that humans are also at risk from this disease. While many bacteria are generally seen to infect specific locations within the human body, Listeria may infect many different locations, such as the brain or the spinal cord membranes or the bloodstream.

Classification:
L. monocytogenes is a gram positive, non-spore forming, motile, facultatively anaerobic, rod shaped bacterium. It is catalase positive, oxidase negative, and expresses a Beta hemolysin which causes destruction of red blood cells. This bacterium exhibits characteristic tumbling motility when viewed with light microscopy. [6] Although L. monocytogenes is actively motile by means of peritrichous flagella at room temperature (20-25C), the organism does not synthesize flagella at body temperatures (37C). [7]

Who gets listeriosis?
Anyone can get this disease, but those at highest risk for serious illness from this bacterium are newborns, the elderly, people with weakened immune systems, and pregnant women. Healthy adults and children occasionally get infected with Listeria, but they rarely become seriously ill. Listeria Monocytogenes is classified as an intracellular paracite. This means that it invades and lives within cells of the body thereby managing to evade the body’s immune system. Infection by as few as 1000 individual bacteria is considered enough for the disease to take hold. When listeric meningitis occurs, the overall mortality may reach 70%; from septicemia 50%, from perinatal/neonatal infections greater than 80%. In infections during pregnancy, the mother usually survives.

When do Listeria infections occur?
Infections occur throughout the year. Although most cases occur sporadically, food-borne outbreaks of this disease do frequently occur. Poor food hygiene and poor personal hygiene conditions are responsible for many of the recently recorded outbrakes.

How is listeriosis spread?
Listeria bacteria are widely distributed in nature and can be found both in water and soil. Infected animals may also serve as sources of contamination. Unlike other organisms, Listeria can be spread through several different methods. Ingestion or food-borne transmission of the organism, such as through the ingestion of unpasteurized milk or by the eating of contaminated vegetables, is often a source of many cases. In newborn infections, the organism can be transmitted from mother to fetus in utero, or directly to the fetus at the time of birth through the contact of the fetus’ blood supply with that of the mothers. Direct contact with the organism can cause lesions on the skin.

What are the symptoms of listeriosis?
Because listeriosis can affect many different parts of the body, the symptoms vary. For meningoencephalitis, the onset can be sudden with fever, intense headache, nausea, vomiting and signs of meningeal irritation. In other body locations, various types of lesions at the site of infection are the primary symptom. In most cases, Listeria infection causes fever and influenza-like symptoms resembling a host of other illnesses.

How soon after exposure do symptoms of listeriosis appear?
Listeriosis has an extremely variable incubation period. It can range from 3 to seventy days, but symptoms usually will typically appear within a month of infection.

How is listeriosis diagnosed?
Specific laboratory tests are the only way to effectively identify this disease. Since many cases may be mild, the disease may be much more common than is realized.

Are there any unusual features of listeriosis?
Listeria infections are a significant risk for pregnant women, who may not experience obvious symptoms. Infection of the fetus can occur before delivery and can cause abortion as early as the second month of pregnancy, but more often in the fifth and six months. An infection later in pregnancy may cause exposure during birth, sometimes resulting in infection of the newborn child which may be fatal.

Does past infection with Listeria make a person immune?
Past infection does not appear to produce immunity.

What is the treatment for Listeria infection?
Several antibiotics are effective against this organism. Ampicillin, either on it’s own or in combination with other types of antibiotics, is frequently used.

What can be done to prevent the spread of Listeriosis?
Since the organism is widly distributed throughout nature, basic sanitary measures such as only using pasteurized dairy products, by only eating cooked meats and washing hands thoroughly prior to the preparation of foods offer the best protection against infection by this disease.

In addition, the following recommendations are for persons who are categorized to be at high risk of infection, such as pregnant women, the elderly and persons with compromised immune systems:

Do not eat hot dogs, luncheon meats, or deli meats, unless they are reheated until they are steaming hot.
Avoid getting the liquid from hot dog packages onto other foods sources, utensils, and food preparation surfaces, and remember to wash hands after handling hot dogs, luncheon meats, and deli meats.
Do not eat soft cheese products such as feta, Brie, and Camembert, blue-veined cheeses, or Mexican-style cheeses such as queso blanco, queso fresco, and Panela, unless they clearly state they are made from pasteurized milk written on the labelling of the product.
Do not eat chilled pâtés or meat spreads. Canned or shelf-stable pâtés and meat spreads can be eaten.
Do not eat refrigerated smoked seafood, unless it is contained in a cooked dish, such as a casserole. Refrigerated smoked seafood, such as salmon, trout, whitefish, cod, tuna or mackerel, is most often labeled as “nova-style,” “lox,” “kippered,” “smoked,” or “jerky.” The fish is found in the refrigerator section or sold over deli counters of grocery stores and delicatessens and supermarkets. Canned or shelf-stable smoked seafood may be eaten.

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