MICROBIOLOGY 101 INTERNET TEXT

CHAPTER XVIX: FOOD MICROBIOLOGY, FOOD BORNE DISEASES


 


REVISION DATE: 11/2/96 


 


TABLE OF CONTENTS

INTRODUCTION

No one doubts the importance of food in our lives. As you learned earlier, all living organisms must have a constant source of energy. This energy may be supplied by materials a cell or organism has stored internally (e.g. our fat or carbohydrate) or it may come from an external source in the environment. Food supplies two major components of life, ENERGY and NUTRITION. Energy is required for the various enzymatic reactions that require an input of energy for the reactions they direct to occur. For example, the movements of muscles in our legs during a race or in our intestines as we digest our latest meal or to draw air into our lungs for breathing all require energy. Those of you who race or otherwise run for pleasure, know that it is advised that you stock up on carbohydrates the day before a race so that you will have a ready supply of available fuel stored in your liver to supply the ATP your muscles will require. As you learned in Chapter VII the glucose, in the form of glycogen in your liver, is oxidized to provide the energy, as ATP, that your muscles need to keep moving. When you run out of that supply you "hit the wall" and have to begin using other sources of energy.

Food also supplies the structural material required for living organisms to make macromolecules for repair of damaged structures or for new construction, such as the manufacturing of offspring. That is, food supplies living organisms with the raw materials necessary for cell construction, as well as other essential components of life such as vitamins and minerals. A balanced and sufficient diet must contains all the calories (units of energy) required to maintain life and the materials for cell maintenance and construction. In this country most of us have never suffered any sort of serious food shortage, nor do we even know anyone who has. Sadly, however, there are pockets of poverty, ignorance and life-style choices that result in some Americans being malnourished to varying degrees. In contrast to our food affluence, educated people know that much of the world's population goes to bed hungry and suffers from constant nutritional deprivation of one kind or another. This condition ranges from full starvation to perpetual lethargy to permanent brain damage of millions of people, mostly children, yearly. It is further common knowledge that any increase in the world's population requires a commensurate increase in food production or starvation becomes inevitable. There is no way around this uncompromising formula.

Microbes play a crucial role in food resources. Microbes are responsible for the loss of much food directly or indirectly through the destruction of the crops and animals that would be used as food. If you doubt this, just search the back regions (if you dare) of your refrigerator for those ugly remains of last month's forgotten leftovers (that furry pizza piece from the party last month). Conversely, microbes are responsible for manufacturing, via their biochemical activities, much of the favorite food we humans enjoy. Further, the microbes, again through their biochemical activities, preserve foods so that we can enjoy them at a later date. Finally, through their activities, microbes are vital to maintaining the fertility of the soil; so much so that we would soon starve if the soil microbes were to vanish. I will discuss the effect of soil microbes in chapter XXI.

SOCIAL ATTITUDES TOWARDS FOOD

To fully understand the food issues, it is necessary to appreciate how much our ideas about food are the result of social learning. For example, everyone is aware that different social groups have different food preferences. A brief walk through downtown Pullman (is there any other kind?) will take you past several ethic eating establishments, offering a tempting variety of cuisine which most of you have probably visited one time or another. Even within our own country we have regional food preferences such as "Southern Cooking" or "Midwestern Cuisine" etc. However, the different preferences in food across the world are huge, including African tribes that live off of fresh cattle blood and yogurt, Asians that drink urine-flavored brews, to Eskimos who enjoy rotted fish. Many of you like buttermilk and cottage cheese, but the English consider the latter to be "spoiled milk". Conversely, many English and Scots relish a pheasant that has been hung out at room temperature for several days until it is rather "ripe". Our local meat counters offer animal intestine and testicles and some students order their pizza covered with small fish that contain their gut contents. Ethyl alcohol, which is the metabolic waste, or urine equivalent, of yeast, is considered nectar-of-the-Gods by people all over the world. The bottom line in all cases is that whatever we label "FOOD", provides us with energy and nutrients and is acceptable on that basis alone. 

 


Have you ever looked at BLUE CHEESE very closely. What is in it (the crunchy bits)? 

FOOD AND HISTORY

Food has played a critical role in history. Archeological evidence suggests that many, perhaps most, ancient civilizations disappeared as a result of being no longer able to feed themselves. The most common reasons cited for this disaster are climate and ecological changes, combined with over population. Conversely, the simultaneous growth in population and the industrial revolution were fueled by new discoveries in agriculture that made it possible to feed many more people a good diet. In history you have been taught about how the "SPICE TRADE" was the driving force behind the intense burst of exploration that inspired Columbus, among others, to make their long and perilous voyages of discovery. Actually it was the microbes that really provided the impetus for those journeys.

We, in the US, have only had widespread refrigeration available for approximately the last 50 years. When I was a young boy, I remember following the ice-man with my friends as he delivered 50 pound blocks of ice to our "iceboxes" on hot summer days. We would grab ice chips from the rear of his truck and suck on them (remember, there was no TV in those days). A 50 lb. block of ice, when placed in an insulated icebox would keep the meat, milk and butter cool for several days and retard their spoilage. It wasn't until the 1940's that my house had an electric refrigerator. In the middle ages foods like meat, milk etc. spoiled quickly, particularly on warm summer days. However, even spoiled meat was nutritious in spite of its rank odor and bad taste, and it beat starvation by a long stretch. Thus people, even the wealthy, frequently ate meat in various stages of active decay. However, they found that if you added SPICES to this spoiled meat the strong flavors the spices imparted covered up the rotten aroma and minimized gagging during dinner. Therefore, spices became the "had to have item" for every good hostess who like to throw parties and impress her guests. Since spices only came from the far east by camel and leaky boats, those that survived the journeys were able to command top prices for this gourmet item. The large profits involved stimulated an intense interest in finding quicker and safer routes to the source of these valuable spices, hence the exploration explosion of the 1400 to 1600s.

Another role of microbes in the middle ages was that of producing miracles. It seems that the damp, dank churches of the middle ages were perfect incubators for the growth of the bacterium Serratia marcescens in the sacramental wafers. Under these conditions the bacterium produces a bright red pigment that resembles BLOOD, thus the appearance of blood-covered holy bread; clearly a miracle in the eyes of the people at that time. Reference: ASM News May 1994. 


 

FOOD PRESERVATION

As supermarkets were rare during most of human evolution, food was in short supply and fresh food was even more limited. Early man may not have been exactly rocket scientists, but they could tell the difference between rotten and not rotten food. So when someone discovered a way to preserve food while it still had a reasonably decent taste and odor they were likely considered a hero. What follows is a description of some of the old and new food preservation methods.

HEAT STERILIZATION

One of the problems with war is that soldiers insist on being fed regularly. In the early 1800s, Napoleon found that his large army could no longer feed itself by stealing from the local peasants and thus his plans to conquer the world were stalled. His solution was to offer a reward for anyone who could figure out how to preserve food so he could take it along with his army, thus keeping them and him happy (the only unhappy ones being those he conquered). In 1810 a man by the name of APPERT found that if he put food in a bottle, jammed a cork tightly in it and placed it in boiling water for an hr or so the contents didn't spoil. BINGO!!, he won the prize, Napoleon got his war, and learned just how cold a Russian winter could get. This procedure, known as STERILIZATION, eventually developed into the canning process. In the process of sterilization all living organisms are destroyed, including bacterial spores. As you will learn later, the most deadly biological toxin is produced by the spore-forming bacterium, Clostridium botulinum. Cl. botulinum is an obligate anaerobe that can grow in seal containers like cans and jars, therefore the canning process is specifically designed to destroy the Cl. botulinum spore. This is achieved by heating food to a minimum of 123oC or 253.4oF for 15 minutes.

In the home, sterilization is carried out using a PRESSURE COOKER. Many of you probably have seen your grandmother, or perhaps your mother, using this container to sterilize home-canned food. The pressure cooker works as follows:

In the microbiology laboratory and commercial canning companies sterilization is achieved by using large containers that operate exactly the same as the home pressure cooker. The laboratory instrument is called an AUTOCLAVE. In commercial canning processes the sterilization containers may be as large as rooms and the food is often wheeled in on large carts. 

 


Can you explain the difference between PASTEURIZATION and STERILIZATION. If not go "directly to jail and do not pass GO or collect your $200". 


 

COOLING AND FREEZING

As describe above, except for Eskimos and other inhabitants of the far north, cooling has only emerged as a common means of preserving food since the mid 1800s when the ice-making machine was discovered. Prior to that time it was common in northern climes for people to cut large blocks of ice from local lakes and to store them in insulated warehouses for use during the summer months to cool their beer and other food items.

Cooling as a preservative is utilized at two levels, 7 to 4oC and -20oC or lower. The higher temperature is commonly used in home refrigerators. At this temperature, the growth of microbes is slowed down but not stopped. Indeed, some microbes (psychrophiles) grow optimally at these temperatures. The failure to prevent spoilage at this higher temperature is attested to by anyone who has attempted to use milk older than two weeks in a refrigerator or who has left fruits and vegetables in a 'frig for extended periods. At the lower temperature the food is frozen. As microbes are unable to grow in frozen material, freezing is one of the most successful means of preserving food with minimal change in flavor or loss of nutritional value. The major draw back to the use of cooling is that (a) it is expensive and (b) it also preserves any pathogens that happen to be present in the food when it was cooled. As a matter-of-fact the storage of living material at temperatures of -70oC or lower is the best way of maintaining them in a state from which they can be subsequently cultured. Such material as sperm, ova, embryos (human and other forms of life), all types of microbes and tissue cells can be frozen and stored for years with little or no loss of viability providing the procedure is carried out properly.

DRYING

Drying as means of preserving food may very well be the oldest method of preservation known to man. Almost certainly it was an accidental discovery made by our primitive ancestors living on the hot plains of Africa. Most likely, our ancestors frequently came across carrion that had dried in the arid conditions. Being hungry, they ripped off the dried meat and chowed down. It didn't take them long to recognize that it wasn't spoiled , that it was light and that it stayed unspoiled as long as it remained dry. Some budding hairy-Einstein soon realized that fresh meat could be dried by placing it in the hot sun and the human race was off to the races, so to speak.

Drying is employed today as a common means of food preservation by all peoples living in warmer climates. Generally the food, such as fresh meat, is cut into small strips and placed on rocks exposed to the sun, or hung over sticks by a campfire. The pieces must be small enough so that the food dries fast enough to prevent spoilage. In the case of meat, one trick is to hang it high enough so the flies can't get to it and lay their eggs in it. As the water evaporates and the food dries, the OSMOTIC PRESSURE increases to a point where microbes are unable to compete with the water-binding material in the food for the remaining water. Since microbes are unable to grow without free (available) water, the food is safe from spoilage, even though it may retain significant water. In some cases (beef jerky) the food is salted prior to drying. The salt is inhibitory to many microbes and contributes to the high osmotic pressure that prevents microbial growth.

SALTS AND OTHER CHEMICALS

SALT OR SODIUM CHLORIDE: The use of salt as a food preservative is probably as old as drying, if not older. All mammals need salt and they will travel long distances to obtain it. Our pre-human ancestors certainly visited the ocean to collect the salt that had dried on the shore and our early human ancestors surely did the same. Occasionally animals or fish must have fallen into pools of sea water that dried in the sun leaving their carcasses impregnated with salt. Again our hungry ancestors were unlikely to turn down a potential meal and they must have recognized that the salted food was unspoiled and remained unspoiled so long as it was covered with salt. The salted food served multiple duty as a source of nutrition and sodium chloride, and as it dried it was easier to transport.

NITRATE (NO3) AND NITRITE (NO2) (SALTPETER): Nitrate and nitrite are used in many foods today as both a preservative and to prevent meat from browning. The bacterium Clostridium botulinum is an obligate anaerobe in that the presence of even a tiny amount of free oxygen prevents its growth. Yet, Cl botulinum readily grows in prepared meats like sausage; the name "botulus" means sausage in German, which should tell you something about the dangers of indulging in sausage in ancient times. Nitrate and nitrite are similar to oxygen chemically, OXIDIZING AGENTS. As such they inhibit the growth of Cl botulinum in foods. In addition, they prevent certain substances in meat from becoming REDUCED, which causes them to turn the meat brown, suggesting that it may be poor quality. In recent years scientists have discovered a link between nitrate/nitite and the formation of carcinogens. As a consequence of this the FDA has required the removal where possible of these chemicals from foods or the lowering of their concentration to the minimal level. The use of nitrate/nitrite poses a classical cost/benefit conflict. That is, is the cost (cancer) of using these substances in our food supply balanced by the protection against death by botulism poisoning? Each of us should decide that ourselves don't you think?

SULFITE (SO2) and VITAMIN C: Most of you have observed the "BROWNING" of fruits and vegetables; the apple you eat turns brown before your very eyes, even as you chow it down. Generally, people feel that "brown" food items are spoiled or at least of lower quality. The browning result from the actions of enzymes in the fruits and vegetables that rapidly react with oxygen to produce brown substances that protect the damaged food from microbes; i.e., the brown chemical is inhibitory to many microbes. This is where sulfite comes in as it is a powerful "REDUCING" chemical and it is inexpensive and effective in tiny amounts AND IT BLOCKS THE BROWING RESPONSE. Therefore it is common to rinse fruits and vegetables in restaurants in solutions containing SULFITE. This insures that items that were prepared several hours before will remain "fresh-looking" all day long on the customer's plates. At the concentrations used, sulfite is not toxic, but a small percentage of people are highly allergic to sulfite and an exposure to even a tiny quantity of it on lettuce etc. may be sufficient to induce a violate allergy attack. This is the reason that restaurants often have signs telling their customers that they are using this material. Another powerful reducing agent that serves the same purpose is vitamin C. This vitamin also is inexpensive, is effective in small amounts, plus it is beneficial to those who ingest it. However, it is more expensive that sulfite and it tends to decay faster, so it is not universally used.

ORGANIC ACIDS: As you recall, all microbes require an optimum pH or acidity in their environment to grow. If there is too much acid or base, a microbe will not grow. As the by-products of many microbial fermentations include the production of chemicals like ACETIC ACID (vinegar), LACTIC ACID, and PROPIONIC ACID it is not too surprising to find that humans, and other life, can actually use these substances as nutrients. However, when they are added to foods in sufficient quantities to lower the pH below that which will support growth, they can serve as natural food preservatives. Again, our ancestors recognized that "SPOILED" foods such as milk and certain vegetables, retained their nutrition upon becoming acidic and remained eatable (preserved) for long periods. Thus was born choice food items like yogurt, sauerkraut, pickles, cheese and buttermilk. Artificial acids, like benzoic acid, inhibit the growth of certain molds, thus it is added to breads and other bakery products that require long shelve lives. In many foods, like the sauerkraut you made in lab, salt is combined with acids to preserve food.

ANTIBIOTICS: Most common antibiotics are inexpensive, stable, safe and effective in small quantities. With their ability to kill or inhibit many microbes, antibiotics might seems as the perfect food preservative. However, all is not what it seems. Using antibiotics for food preservation is like using 100 dollar bills for toilet paper; it gets the job done but it is not the best use for that item. As you've learned in Chapter X, we are in grave danger from infections produced by antibiotic-resistant microbes. The use of antibiotics in preserving food and in animal feeds has been demonstrated to increase the spread of antibiotic resistance between pathogens. Although some action has been taken to limit the use of antibiotics for these purposes, it is still done in many places.

RADIATION:

Atomic radiation is becoming widely used in the preservation of food. Many of the prepared meals available on the supermarket shelves at room temperature have been sterilized that way. Atomic radiation is lethal to all life when used in high doses. To sterilize food by this technique, the food is placed in a protected room and exposed to a high dose, usually of gamma radiation, from radioactive wastes refined from atomic power plants. A dosage that had been determined to be lethal to all microbes, including bacterial spores, is used.

FAQ:

1. Does exposure to radiation make the food radioactive?

ANSWER: No. There is no residual radiation contaminating food exposed to high doses of the radiation used.

  1. Does the treatment produce dangerous chemicals in the radiated food?
ANSWER: Although there is still some debate over this, the majority of the available scientific evidence does not support this contention. There is no doubt that the high radiation does induce some chemical changes in the food, but there is no proof that any of these materials are harmful.
  1. Would you eat radiation treated foods?
ANSWER: Yes. However, I consider every new technology suspect until long use proves otherwise, so I try to keep myself informed on this and other technological matters; I would advise that you do the same.

Remember that the microwave oven uses a form of radiation to cook the food placed in it and we have accepted its almost universal use without much concern.

SALTING/PICKLING/SUGAR:

I have discussed salting above, but mention it here as salt is often used in combination with organic acids to preserve foods. As you learned in lab, when making sauerkraut, the addition of salt changes the environment so that different microbes can grow and change the flavor of the food in a preferred way. Sugar is also used in jams and jellies as a preservative. It acts the same way that salt does in that both bind up the available FREE-WATER chemically so tightly that it is not available to most microbes. However, as you've probably all observed when you've opened that jam-jar stored in the 'frig since last Xmas and found a mass of hairy mold attempting to ooze out of the jar, there are microbes that can grow at high sugar concentrations; they are called saccharophiles (sugar-loving). You learned previously that there are HALOPHILES that can grow on salted fish and in saturated salt-water.

SMOKING:

Smoking is another ancient means of preserving food. Smoking was probably a serendipitous side effect of the discovery of drying food. Our ancestors must have frequently stumbled on the partly cooked remains of animals killed in fires and they certainly tore off the smoked and dried pieces of flesh and ate them. They may have realized then, or more likely, after they had tamed fire, that chunks of food, left in the smoke of the fire while they were off hunting or otherwise entertaining themselves, dried out and remained eatable for long periods. Plus the food absorbed pleasing flavors. When foods are smoked they absorb various chemicals from the smoke including aldehydes and acids. The former is lethal to many microbes and the latter, lowers the pH of the meat. There is danger lurking in this process. Aldehydes are carcinogenic and people who eat a heavy diet of smoked foods suffer disproportionately from cancer of the mouth, stomach and esophagus. Perhaps this is another case of the "dangers of secondhand smoke".

 

FOOD BORNE DISEASE

Since the nutrients in the foods we ingest are the very same nutrients that microbes thrive on, it is logical that the microbes are among our greatest competitors for the available organic food. Food borne diseases, or FBD, have always plagued man, and for that matter every other living animal on the planet, for several reasons. First, for most of our evolution humans have existed in filth and squalor the extent of which most of my gentle readers can not begin to imagine. Not only were we usually covered in dirt and various forms of gore and muck, but our food, often taken from the partly rotted carcasses of long-dead creatures, was covered with even worse. No matter, since our ancestors were hungry, probably near to starving a goodly portion of the time, the niceties of sanitation were rarely observed. Rather, our ancestors bolted down any food that fell into their fouled hands regardless of its condition. If they were really lucky they didn't get sick, if they were mildly unlucky they got a few cramps and a brief, but messy case of the runs and recovered. However, if they really had bad fortune they became violently ill and frequently died writhing in agony in their own vomit and excrement. Secondly, many pathogens have evolved to take advantage of the gusto with which humans ingest unsanitary meals to gain entry into our nutrient-rich bodies by hitching a ride in our food for their own nefarious ends. If you think I'm overstating this case just watch an unsupervised small child eat, but don't blame me if you get nauseous.

Food Borne Diseases exist in two major categories; INTOXICATIONS and INFECTIONS. The former is the result of ingesting toxins produced by microbes that have grown on the food prior to it being eaten. The latter is the result of the food serving as a fomite that carries an infectious pathogen deep into the juicy recesses of a body where it is able to gain a foothold. Once established the pathogen grows and produces a disease as previously described. What follows is a brief description, by no means inclusive, of the major FBD including the names of the perpetrators, the disease mechanism, when known, of how they produce a disease state, their prognosis and treatment.

The CDC has available an excellent description of FBD in the Internet which I would advise all of my readers to view before (or after) reading my material below. 

BOTULISM

Botulism is an intoxication that is caused by the ingestion of a virulent nerve toxin produced by the growth of the gram positive, obligate anaerobe, spore-former Clostridium botulinum. This bacterium appears to be a normal inhabitant of the soil, hence its ready contamination of most foods. It is able to grow in absence of oxygen in a wide variety of foods and in so doing produces a protein neural toxin, two to three grams of which would be sufficient to kill every human on earth. However, the organism will not grow in the presence of oxygen or nitrate salts and it does not produce the toxin at pH below 4.7. Only one strain is able to produce the toxin at refrigerator temperature; that which is found associated with marine organisms. Being a protein, the toxin is destroyed by boiling it at 100oC for 10 to 15 min. However, the spore requires a temperature of 121oC for 15 min to kill it.

The toxin acts by binding to nerve junctions and destroying the nerve. The symptoms, which occur usually within 12 to 36 hours, but which can take up to 8 days to appear, classically consist of double vision, dizziness, inability to speak, breath or swallow. Death often occurs due to the inability to breath. The only treatment is the injection of antitoxin to the several varieties of the toxin. This treatment is only effective against any free toxin, once the toxin has bound to the nerves the damage is irreversible. The entire canning process is built around insuring that all spores of this bacterium contaminating any canned food are destroyed in the sterilization process. Industry has a sterling record in that deaths from commercial-botulism are very rare. This is influenced by the fact that once a product is known to contain botulism toxin none of that product is ever again purchased by a customer. The majority of botulism poisonings occur in HOME-CANNED FOODS prepared by grandma or your favorite aunt. A rule of thumb is "READ THE BLOODY CANNING DIRECTIONS" and if you think a food might contain the botulism toxin never taste even the smallest drop of it!

Some interesting additional information about this disease is:

Q FEVER

This FBD is the result of infection by the gram negative, obligate intracellular bacterium Coxiella burnetti. This organism is associated with farm animals, with man usually considered to be an accidental victim; in fact it was first called the "wool cutters' disease" because Australian wool clippers frequently came down with it because of their close contact with sheep. It is still a common disease among those that work with farm animals where it is spread in the dust and through direct contact with animal carriers. It produces a flu-like disease that varies from being mild to very debilitating. Although the majority of people who contact this disease recover, some strains of the bacterium are able to infect the heart, producing a fatal disease. Because it is highly infectious, the onset rapid and the disease debilitating, it has been studied as a biological warfare weapon. The microbe produces forms which are spore-like in their resistance to heat and drying. Because of the frequency of milk contamination by C. burnetti is considered a FBD and because of the heat-resistant nature of this bacterium, the temperature of the pasteurization process was increased a few years ago to 72oC for 15 seconds to eliminate it from milk. Click here to see an EM picture of this bacterium. It so happens that the chairman of our department is one of the world's leading research investigators of C. burnettii and his laboratory has been responsible for developing a vastly improved diagnostic test for it.

STAPHYLOCOCCUS AUREUS FOOD POISONING

As you learned in lab exercise ??, the gram positive coccal-bacterium Staphylococcus aureus is a common inhabitant of the human body, being found on our skin and in our nose and is considered part of our natural flora. This bacterium interacts with humans in many ways. It is a common cause of nosocomial infections that frequently causes death in the patients it infects, it is a prevalent cause of severe skin infections like boils and impetigo, it is the etiological agent of TOXIC-SHOCK SYNDROME and it is one of the major causes of FBD in the world because of its intimate association with humans. This bacterium has a number of characteristics that contribute to its many roles. Although it is not a spore-former, it does tolerate high temperatures better than most non-spore-former. It is able to grow in high salt and sugar environments which allows it to survive and flourish on the human skin and in rich, sweet foods. It produces a wide variety of toxins, depending on the strain and it tends to carry a large number of antibiotic resistant plasmids. It is, in short, a formidable adversary.

It generally produces FBD in "rich foods", such as cakes, pies, potato salad and custards. The usual scenario involves food that was prepared in advance and improperly stored for a long time before being eaten. During this storage period the contaminating S. aureus (from the nose and hands of the individual who prepared the food) grow rapidly, often in such perfusion that their yellow colonies can be observed upon close examination. During growth the bacteria produce a number of potent toxins, one of which, called a SUPERANTIGEN, mimics a protein involved in our immune response. This superantigen acts by over stimulating the T-cells to produce prodigious quantities of interleukin 2 which, in turn, induces fever, malaise, nausea, vomiting, diarrhea and shock, which are the classical symptoms of staph food poisoning. This was discovered serendipitously by a physician who was treating cancer patients with interleukin 2 at different dosages and he noticed that at high doses they developed the classical food poisoning symptoms. There is a classical article in the Scientific American Apr. 1992 chronicling this fascinating story.

Staph food poisoning symptoms usually appear within 1 to 6 hours after ingestion and produces the symptoms described above. The disease is usually over within 24 hours and death is rare, usually limited to the very young or the old and infirmed. The best way to avoid this disease will be summarized below. Click here for a n EM picture of S. aureus.

SALMONELLA GASTROENTERITIS

Infections of humans by a variety of salmonella species is quite common, particularly in third world countries. The Salmonella are a genus of gram negative, small rod-shaped, non-spore-forming bacteria that are usually associated with animals, both wild and domestic. The problem occurs because many of the animal strains of Salmonella, including ones that live in snakes, turtles and lizards, as well as chickens, horses, and turkeys, can infect humans and cause a severe gastroenteritis. This bacterium is released in the feces of the infected animal, thus when humans contract this disease it usually means that they have ingested fecal material due to unsanitary behavior. Probably the most common sources of human infection occurs in the kitchen, both commercial and domestic. Unless the HIGHEST STANDARDS OF SANITATION are applied by knowledgeable individuals during the slaughter and preparation of food for human consumption, fecal material can contaminate the food. Such contamination can easily be spread to other foods via kitchen utensils, cutting boards, by contaminated hands or contact with contaminated work surfaces. The Salmonella are hardy microbes that are able to survive outside their hosts in water, on moist surfaces etc. for days to months, so cursory measures will not protect you from these dangerous pests.

The most common sources of Salmonella infection are fecal-contaminated animal meats such as turkey, chicken, beef etc. and eggs . Victims ingest the bacteria which invades the intestinal mucosa setting up an infection that produces inflammation of the intestine resulting in diarrhea, fever, cramps, nausea, abdominal pain, and vomiting (GASTROENTERITIS). The disease onset occurs within 8 to 48 hours and the disease lasts 2 to 5 days to as long as several weeks. Treatment involves fluid/electrolyte replacement; antibiotics are only used to counter secondary infections. A serious, new form of Salmonella has appeared in the US in the past 10 years. This is a disease caused by Salmonella enteritidis. This bacterium has developed the ability to grow in the ovary or egg-producing organ, of chickens where it is deposited within the egg as it is being formed. Other egg-related Salmonella are found on the exterior of the egg where they can be killed by washing with bleach or hot soapy water, however this new strain can only be killed by thoroughly cooking all parts of the egg. That is, the bacterium is NOT ELIMINATED from soft-boiled eggs or "over easy" eggs. The disease produced by S. enteritidis has caused a number of deaths and is a threat to anyone who fails to cook their eggs properly, however it is not considered a major health problem. In our household we always cook anything with egg in it thoroughly. The disease can only be prevented by testing of egg-producing flocks and the elimination of all the infected chickens. One common problem is the way in which eggs are stored prior to placement on the store shelves. In a recent investigation it was found that while the FDA rules specify that eggs should be stored at temperatures low enough to prevent the growth of S. enteritidis in them, many handlers do not adhere to these rules and examples of eggs being stored at room temperature for several days were found. Perhaps you should inquire of you supermarket manager how their eggs are stored prior to be placed out for sale.

CLOSTRIDIUM PERFRINGENS

Clostridium perfringens is a gram positive, obligate anaerobic, spore-former that is found in the gut of many animals, including humans. Besides producing a FBD, it is responsible for producing gas gangrene. As with Salmonella, C. perfringens contamination occurs via the fecal-oral route during slaughtering and food preparation. However, this disease is an INTOXICATION and not an infection. As with Staphylococcus food poisoning, this FBD is usually the result of improper storage of food prepared in advance. A typical scenario goes something like this. A holiday turkey is prepared, however during preparation the stuffing gets contaminated with C. perfringens spores left on the turkey during their slaughter. The stuffing is subsequently packed tightly inside the turkey which is cooked. Because stuffing is a excellent insulator, it may not get hot enough to kill the heat-resistant spores. At the first serving of the turkey no disease occurs, however once the stuffing, containing the live spores reaches room temperature the spores germinate and begin to grow rapidly while producing toxins. As the stuffing sits out for several hours before being stored in the refrigerator in a large bowel, bacterial growth continues and since the large mass of stuffing may take several hours to cool down in the refrigerator, growth continues for several more hours. When the "leftovers" are eventually served they contain toxic quantities of bacterial products and the eaters become ill. The illness strikes within 8 to 16 hours and produces profuse diarrhea. Most victims recover in 1 to 4 days and no treatment is usually necessary except for the very young or the elderly.

ESCHERICHIA COLI 0157:H7

This is the new kid on the block in that the disease produced by this bacterial strain was first recognized in 1982 during an outbreak of a FBD here in the State of Washington. E. coli is a normal inhabitant of the human and animal gut and is the most studied bacterium on the planet. It is a gram negative, motile, plump, non-spore-forming rod. The numbers 0157 and H7 refer respectively to the antigenic characteristics of LPS and a flagellar protein. Although this strain had been first reported in 1975 it was not recognized as a FBD organism until the 1982 epidemic. It is likely that there had been many previous outbreaks of food poisoning involving this bacterium, but the etiological agent had not been recognized and the FBD had been blamed or other organisms. This bacterium enter its victims via the fecal-oral route and produces and infection in the victim's intestine. 0157:H7 contains a plasmid that carries the gene for a virulent toxin. Once the infection is established, the toxin is released and causes HEMMORRHAGIC COLITIS and HEMOLYTIC UREMIC SYNDROME. The former results in damage of the intestine accompanied by bleeding and in sever cases destruction of the intestine that can only be stopped by surgical removal of the infected tissue. In the latter syndrome, the kidney is severely damaged and often completely destroyed. Death results from general organ failure due to a combination of the toxin effects and the failure of crucial organs.

The bacteria resides in food that is contaminated with fecal material, usually from cattle, although other sources may exist, including humans. The bacterium is easily killed by heat, but if products like hamburgers are not heated so that all parts of the patty reach a lethal temperature, the organism can be survive to cause the disease. This bacterium has been cultured from raw milk, cheese, turkey roll sandwiches, chicken, pork, and raw vegetables; and recently in unpasteurized fruit juice. It has been spread between children at nursery schools due to unsanitary conditions. The onset of the disease occurs 24 to 72 hours after ingestion. It varies from a mild gastroenteritis to the severe, often deadly course described above. Antibiotics seems to have little effect probably because once tissue damage sets in the blood supply is interrupted which prevents the drugs from reaching the infected sites. Surgical removal of the infected tissue is useful but very traumatic and it may not remove all the infection. It appears to be more severe in small children, possibly because they have not developed general low level immunity to E. coli.

The extent and seriousness of this disease was painfully illustrated by events that took place in Japan during the summer of 1996. Almost 6,000 people became ill with 0157:H7 and to this day the source of the infection is unknown.

TRAVELER'S DIARRHEA and OTHER E. coli INFECTIONS

The bacterium E. coli is the etiological agent of a whole range of water and food borne diseases. One of the more common is a disease known as TRAVELER'S DIARRHEA. As its name implies this disease usually hits a traveler 1 to 3 days after he/she has arrived in a foreign country and consists of everything from a mild case of loose stools to a full blown case of painful diarrhea where one is confined to staying within 10 feet of a toilet until it passes. The symptoms usually disappear within 1 to 3 days and it is treated with anti-diarrhea drugs. A traveler may suffer subsequent attacks as they visit other countries or they may never suffer an attack. The disease is thought to be a result of the strain specific nature of local E. coli. That is, because of a variety of environmental factors E. coli in different populations accumulate a unique series of genetic characteristics to which the infected population is adapted. However, a visitor who eats the local fecal-contaminated food and/or water picks up this unique regional-strain quickly. As it reproduces in the visitor's intestine it produces slightly different set of toxins to which the new host reacts unfavorably, as evidenced by their developing a case of the trots (or as it is called locally, the Palouse Two Step).

A number of other pathogenic E. coli strains have been identified each of which produces its characteristic intestinal disease. Some of these strains are virulent, and can produce a fatal disease while other produce relatively mild diseases. Each strain has been identified by a variety of characteristics including their antigenic "fingerprint", the plasmids they contain and now their DNA fingerprints. The E. coli induced diarrhea is a major, if not the major cause of death around the world of young babies. Usually the babies catch these organisms through drinking contaminated water, often used to make their formula. One of the unintended consequences of introducing baby formulas into underdeveloped countries is an increase in infant death from diarrhea as the mother switch to formula made with contaminated water from breast feeding.

THE PREVENTION OF FBD or MOMMIE WAS RIGHT

The prevention of FBD is theoretically easy but practically difficult due, as in the case of STD, the nature of humankind. Basically their elimination requires the rigorous application of basic rules of hygiene and sanitation that everyone learns in kindergarten but frequently fails to apply in everyday life. Your MOMMIE told you all the following and she was right on:
  1. Wash your hands after pooping, especially if you're going to be handling food for yourself or anyone else (like me).
  2. Wash your hands after playing with the dog, cat, ferret or alien, especially if you're going to be handling food for yourself or anyone else (like me).
  3. Wash your hands after playing in the dirt, especially if you're going to be handling food for yourself or anyone else (like me).
  4. Don't eat dirty or spoiled food (DUH!).
  5. Don't eat off of dirty dishes or utensils (double DUH!).
  6. Develop good KITCHEN HABITS, which include the following
All of these suggestions add up to one thing: AVOID EATING FECES (or if you're going to eat it make sure it is well cooked!).

MODERN PROBLEMS OF FOOD SAFETY

Modern issues of safe food revolve around two things, FAST FOODS and PREPARED FOOD. Many of the readers have, as I have, worked in the Fast Food business. Typically these businesses hire young, untrained, and often uneducated people. Such individuals are ignorant of routine sanitary measures or don't understand their significance. Further, there is a large turnover in these jobs, so trained individuals are frequently being replaced with new, untrained personnel. These businesses emphasize speed and service efficacy and they usually use bulk food supplied from a central source over which they have no control. All of this makes the balance between profit, speed and hygiene difficult to maintain. Although the food services are highly regulated by state, federal and local health organizations there rarely are enough trained inspectors to insure that all these facilities maintain sanitary conditions at all times. Since the public responds harshly to the report of unsafe food being supplied by a business by boycotting that business, or suing it to extinction, it is ultimately in the interest of the business owners and employees to maintain high standards of health and safety. The long distance shipping of prepared food is another area of concern. The vehicles that food is transported in may be used for the transporting of toxic materials between moving food and cleaning between jobs may not be performed properly. Further, since most food should be refrigerated, it is important that the proper temperatures be maintained during its transportation and this doesn't always occur.

The ubiquity of the MICROWAVE in our kitchens also has added a set of new problems and concerns about the microbial safety of our food supplies. The supply of prepared, sterilized foods stored at room temperature on the supermarket shelves presents a potential source of microbial contamination. Frozen foods for microwave preparation have been available for a number of years and there have been some problems. The nature of the microwave means that the food is heated from the INSIDE OUT in contrast to the traditional way of cooking. A number of food poisoning cases involving frozen microwave foods have been traced to this difference. In several cases the food was cooked properly on the inside, but the interior heat had not reached the contaminated skin or surface of the food and the contaminating microbes there were not killed. Microwave instructions inform the user that it is necessary to allow "STAND TIME" so the heat from the interior can reach the outer skin of the food, but the rushed nature of our busy lives makes it difficult to follow these instructions. However, it is better to take the time compared with losing 5 feet of your small intestine and half your kidney function to E. coli 0157:H7 isn't it?

OTHER FOOD BORNE DISEASES

There are a number of other FBD that I have chosen not to discuss. These include Campylobacteriosis, Listeriosis, Yersinosis and Vibrio parahaemolyticus. All are serious diseases.