The Relationship of Microorganisms to
Sanitation
Knowledge of the role of microorganisms in food spoilage and foodborne illness is needed to understand the principles of food sanitation. Microorganisms (also called microbes and microbial flora) are found throughout the natural environment. Effec-tive sanitation practices are needed to com-bat their proliferation and activity.
HOW MICROORGANISMS RELATE TO FOOD SANITATION
Microbiologyis the science of microscopic forms of life known as microorganisms. Knowledge of microorganisms is important to the sanitation specialist because their con-trol is part of a sanitation program.
Microorganisms Common to Food
A major challenge for the sanitarian is to protect the production area and other involved locations against microbes that can reduce the wholesomeness of food. Microor-ganisms can contaminate and affect food, with dangerous consequences to consumers. The microorganisms most common to food are bacteria and fungi. The fungi, which are less common than bacteria, consist of two major microorganisms: molds (which are multicellular) and yeasts (which are usually unicellular). Bacteria, which usually grow at the expense of fungi, are unicellular. Viruses, although transmitted more from person to person than via food, should also be men-tioned because they may contaminate food as a consequence of poor employee hygiene.
Molds
Molds have been considered beneficial and troublesome, ubiquitous microorgan-isms. They often work in combination with yeasts and bacteria to produce numerous indigenous fermented foods and are involved in industrial processes to produce organic acids and enzymes. Molds are a major con-tributor to food product recalls. Most do not cause health hazards, but some produce mycotoxins that are toxic, carcinogenic, mutagenic, or teratogenic to humans and animals.
Molds spread because they may be air-borne. These fungi cause various degrees of visible deterioration and decomposition of foods. Their growth is identifiable through rot spots, scabs, slime, cottony mycelium, or colored sporulating mold. Molds may pro-duce abnormal flavors and odors due to fermentative, lipolytic, and proteolytic changes caused by enzymatic reactions with carbohydrates, fats, and proteins in foods.
Molds have an absolute requirement for oxygen and are inhibited by high levels of carbon dioxide (5% to 8%). Their diversity is evident through the ability to function as oxygen scavengers and to grow at very low levels of oxygen and even in vacuum pack-ages. Some halophilic molds can tolerate a salt concentration of over 20%.
Yeasts
Yeasts are generally unicellular. They differ from bacteria in their larger cell sizes and morphology, and because they produce buds during the process of reproduction by fission. The generation time of yeasts is slower than that of bacteria, with a typical time of 2 to 3 hours in foods, leading from an original contamination of one yeast/g of food to spoilage in approximately 40 to 60 hours. Like molds, yeasts can be spread through the air or by other means and can alight on the surface of foodstuffs. Yeast colonies are generally moist or slimy in appearance and creamy white. Yeasts prefer an Aw of 0.90 to 0.94, but can grow below 0.90. In fact, some osmiophilic yeasts can grow at an As low as 0.60. These microorganisms grow best in the intermediate acid range, a pH of from 4.0 to 4.5. Yeasts are more likely to grow on foods with lower pH and on those that are vacuum packaged. Food that is highly contaminated with yeasts will frequently have a slightly fruity odor.
Bacteria
Bacteria are unicellular microorganisms (prokaryotic cells) that are approximately 1 m in diameter, with morphology variation from short and elongated rods (bacilli) to spherical or ovoid forms. Cocci (meaning “berry”) are spherically shaped bacteria. Individual bacteria closely combine in various forms, according to genera. Some sphere-shaped bacteria occur in clusters similar to a bunch of grapes (e.g., staphylococci). Other bacteria (rod-shaped or sphere-shaped) are linked together to form chains (e.g., Streptococci). Also, certain genera of sphere-shaped bacteria are formed together in pairs (diploid formation), such as pneumococci. Microorganisms, such as Sarcinia spp., form as a group of four (tetrad formation). Other genera appear as an individual bacterium. Some bacteria possess flagella and are motile.Bacteria produce pigments ranging from variations of yellow to dark shades, such as brown or black. Certain bacteria have pig-mentation of intermediate colors—red, pink, orange, blue, green, or purple. These bacteria cause food discoloration, especially among foods with unstable color pigments, such as meat. Some bacteria also cause dis-coloration by slime formation.Some species of bacteria produce spores, which may be resistant to heat, chemicals, and other environmental conditions. Some of these spore-forming bacteria are ther-mophilic microorganisms that produce a toxin that can cause foodborne illness.
Viruses
Viruses are infective microorganisms with dimensions that range from 20 to 300 nm, or about 1/100 to 1/10 the size of a bacterium. Most viruses can be seen only with an elec-tron microscope. A virus particle consists of a single molecule of DNA or RNA, sur-rounded by a coat made from protein. Viruses cannot reproduce outside of another organism and are obligate parasites of all liv-ing organisms, such as bacteria, fungi, algae, protozoa, higher plants, and invertebrate and vertebrate animals. When a protein cell becomes attached to the surface of the appropriate host cell, either the host cell engulfs the virus particle or the nucleic acid is injected from the virus particle into the host cell, as with bacteriophages active against bacteria.
In animals, some infected host cells die, but others survive infection with the virus and resume their normal function. It is not necessary for the host cells to die for the host organism—in the case of humans—to become ill (Shapton and Shapton, 1991).
Employees may serve as carriers and trans-mit viruses to food. An infected food handler can excrete the organism through the feces and respiratory tract infection. Transmission occurs through coughing, sneezing, touching a runny nose, and from not washing the hands after using the toilet. The inability of host cells to perform their normal function causes illness. After the normal function is reestablished, recovery from illness occurs. The inability of viruses to reproduce them-selves outside the host and their small size complicates their isolation from foods suspected of being the cause of illness in humans. Foodborne viruses cause diseases through viral gastroenteritis or viral hepatitis. A virus that has caused a major increase in out-breaks in restaurants during the past 10 years is hepatitis A. Intravenous drug use is one factor that accounts for some of this rise. Infectious hepatitis A can be transmit-ted through food that has not been handled in a sanitary manner. The onset is 1 to 7 weeks with an average length of 30 days.
Symptoms include nausea, cramps, vomit-ing, diarrhea, and, sometimes, jaundice, which can last from a week to several months. A major source of hepatitis is raw shellfish from polluted waters. The most likely foods to transmit viral illnesses are those handled frequently and those that receive no heating after handling, such as sandwiches, salads, and desserts. Because this disease is highly contagious, it is mandatory that employees handling food practice thorough hand washing after using the toilet, before handling food and eating utensils, and after diapering, nursing, or feeding infants. Viruses also cause diseases
such as influenza and the common cold.
EFFECTS OF MICROORGANISMS ON FOODBORNE ILLNESS
Foodborne Disease
A foodborne disease is considered to be any illness associated with or in which the
causative agent is obtained by the ingestion of food. A foodborne disease outbreak is
defined as “two or more persons experiencing a similar illness, usually gastrointestinal,
after eating a common food, if analysis identifies the food as the source of illness.”
Approximately 66% of all foodborne illness outbreaks are caused by bacterial
pathogens.
Of the 200 foodborne outbreaks reported each year, approximately 60% are of unde-
termined etiology. Unidentified causes may be from the Salmonella and
Campylobacter species, Staphylococcus aureus, Clostridium perfringens, Clostridium
botulinum, Listeria monocytogenes, Escherichia coli O157, Shigella, Vibrio, and
Yersinia enterocolitica, which are transmitted through foods. A wide variety of home-
cooked and commercially prepared foods have been implicated in out-breaks, but they
are most frequently related to foods of animal origin, such as poultry, eggs, red meat,
seafood, and dairy products.
FOODBORNE ILLNESSES
Food poisoning is considered to be an ill-ness caused by the consumption of food
containing microbial toxins or chemical poisons. Food poisoning caused by bacterial
toxins is called food intoxication; whereas, that caused by chemicals that have gotten
into food is referred to as chemical poisoning.
Illnesses caused by microorganisms exceed those of chemical origin. Illnesses that
are not caused by bacterial by-products, such as toxins, but through ingestion of
infectious microorgan-isms, such as bacteria, rickettsia, viruses, or parasites, are
referred to as food infections.
Foodborne illnesses caused from a combination of food intoxication and food
infection are called food toxico infections. In this food-borne disease, pathogenic
bacteria grow in the food. Large numbers are then ingested with the food by the host
and, when in the gut, pathogen proliferation continues, with resultant toxin production,
which causes ill-ness symptoms.
Aeromonas hydrophila Foodborne Illness
Evisceration and cold storage of chickens at 3ºC may permit an increase in A.
hydrophila. Chill waters and the evisceration process itself appear to be probable
sources of contamination in the typical broiler processing operation and may contribute
to the high efficiency of occurrence of this microorganism at the retail level. The
temperature range for growth is 4ºC to 43ºC with an optimum of 28ºC. The pH range
is 4.5 to 9.0 and the maximum concentration of salt for growth is 4.0%. A. hydrophila
can cause gas-troenteritis in humans and infections in patients immunocompromised
by treatment for cancer.
Bacillus cereus Foodborne Illness
Bacillus cereus is a gram-positive, rod-shaped, spore-forming obligate aerobe that
is widely distributed. Although some strains of this microbe are psychrotrophic and
able to grow at 4 to 6ºC, most proliferate at 15 to 55ºC with an optimal temperature of
30ºC. The normal habitat for B. cereus is dust, water, and soil. It is found in many foods
and food ingredients. Because this microorganism is a spore-former, it is heat resistant.
Most of the spores have moderate resistance, but some have high heat resistance. The
pH range for the proliferation of this bacterium is 5.0 to 8.8 with a minimum Aw of
0.93.
In the emetic form of B. cereus illness, the symptom is primarily vomiting (which
occurs within 1 to 6 hours after infection and endures for 24 or less hours), although
diarrhea may occur also. The B. cereus emetic toxin is performed in the food and, like
Streptococcus faecalis, it is heat stable. The emetic form, which is more severe than
the diarrhetic type, is caused by the production of an enterotoxin within the gut.
Outbreaks have occurred as a result of consuming rice or fried rice served in restau-
rants or from warmed-over mashed pota-toes. Other foods associated with this food-
borne illness include cereal dishes, vegetables, minced meat, meat loaf, milk products,
soups, and puddings. The number of cells required for an outbreak is 5 to 8 log colony-
forming units (CFU) per gram of food. This illness is best controlled by proper
sanitation in restaurants and by holding starchy cooked foods above 50ºC or
refrigerating at below 4ºC within 2 hours after cooking to prevent growth and toxin
production.
Botulism
Botulism is a foodborne illness that results from the ingestion of a toxin produced by
C. botulinum during its growth in food. This microbe is an anaerobic, gram-positive,
rod-shaped, spore-forming, gas-forming bacterium that is found primarily in the soil.
The optimal growth temperature is 30 to 40ºC. Temperature growth ranges are
normally 10 to 50ºC except for type E, which thrives at 3.3 to 45Cº. Infants can be
affected by this disease through the ingestion of as few as 10 to 100 spores that
germinate in the intestinal tract and produce toxin. Death occurs in approximately 60%
of the cases from respiratory failure.
Because C. botulinum may occur in the soil, it is also present in water. Therefore,
seafoods are a more viable source of botulism than are other muscle foods. However,
the largest potential sources of botulism are home-canned vegetables and fruits with a
ow to medium acid content. Because this bacterium is anaerobic, canned and vacuum-
packaged foods are also viable sources for botulism. Canned foods with a swell should
not be eaten because the swelling results from the gas produced by the organism.
Smoked fish should be heated to at least 83ºC for 30 minutes during processing to
provide additional protection.
To prevent botulism, effective sanitation, proper refrigeration, and thorough cooking
are essential. This toxin is relatively heat-labile, but the bacterial spores are very heat-
resistant, and severe heat treatment is required to destroy them. Thermal process-ing at
85ºC for 15 minutes inactivates the toxin. The combinations of temperatures and times
given in Table 3–2 are required to destroy the spores completely.
Campylobacteriosis
Campylobacter has become a major concern because it is transmitted by food, especially inadequately cooked foods and through cross-contamination. The tempera-ture for growth ranges from 30 to 45.5ºC with an optimum of 37 to 42Cº. It survives to a maximum sodium chloride level of 3.5% and is inhibited by 2.0%. Campylobacter is commonly found as commensals of the gastrointestinal tract of wild and domesticated animals. This fastidious, facultative (microaerophilic-requiring 5% O2 and 10% CO2),
gram-negative, non-spore-forming, spiral curve-shaped rod, which is motile by means of flagella, It has been identified as the causative agent of veterinary diseases in poultry, cattle, and sheep, and is quite common on raw poultry. As detection and isolation of this microorganism have been improved, it has been incriminated in foodborne disease out-breaks. This microbe is now recognized as one of the most frequent causes of bacterial diarrhea and other illnesses, and there is a mounting body of evidence that it causes ulcers.Campylobacter is found in the intestinal tract of cattle, sheep, swine, chickens, ducks, and turkeys. Because this microorganism is found in fecal material, muscle foods cancontaminated during the harvesting process if sanitary precautions are not observed. Campylobacter jejuni has also been detected in milk, eggs, and water that have been in con-tact with animal feces.
Campylobacter outbreaks have occurred most frequently in children over 10 years old and in young adults, although all age groups have been affected. This infection causes both the large and small intestines to pro-duce a diarrheal illness. Although symptoms may occur between 1 and 7 days after eating contaminated food, illness usually develops 3 to 5 days after ingestion of this microbe.Clostridium perfringens Foodborne Illness-Cl. perfringens is an anaerobic, gram-positive, rod-shaped, spore-former that produces a variety of toxins as well as gas during growth. This microbe will proliferate at a temperature range of 15 to 50ºC with an optimal temperature of 43 to 46ºC. The optimal pH range is 6.0 to 7.0, but growth can occur from pH 5.0 to 9.0. The minimum Aw for growth is 0.95 to 0.97. This microorganism-ism has a sodium chloride maximum of 7.0 to 8.0% and is inhibited by 5.0%. C. perfringens and their spores have been isolated in many foods—especially among red meats, poultry, and seafood. The spores from various strains of this microorganism have differing resistances to heat. Some spores are killed in a few minutes at 100ºC, whereas others require from 1 to 4 hours at this temperature for complete destruction. C. perfringens can be controlled most effectively by rapid cooling of cooked and heat processed foods. Frozen storage at –15ºC for 35 days provides greater than 99.9% kill of this microorganism. An out-break of
foodborne illness from C. perfrin-gens can usually be prevented through proper
sanitation as well as appropriate holding (≥60ºC) and storage (≤2ºC) temper-atures of foods at all times, especially of left-overs. Leftover foods should be reheated to 65ºC to destroy vegetative microorganisms.
Escherichia coli O157:H7 Foodborne Illness
Outbreaks of hemorrhagic colitis and hemolytic uremic syndrome caused by E. coliO157:H7, a facultative anaerobic, gram-negative, rod-shaped bacterium, have elevated this pathogen to a high echelon of concern. It is uncertain how this microorganism mutated from E. coli, but some scientists speculate that it picked up genes from Shigella, which causes similar symptoms.
This microorganism is shed in the feces of cattle and can contaminate meat during pro-cessing. It is important to establish interven-tion procedures during harvesting and meat processing operations to control the prolifer-ation of this pathogen. Until approval of an absolute critical control point, such as irradiation, beef should be cooked to 70ºC to ensure sufficient heat treatment to destroy this pathogen. A rigid sanitation program is essential to reduce foodborne illness out-breaks from this microorganism.
E. coli O157:H7, which is designated by its somatic (O) and flagellar (H) antigens, was discovered as a human pathogen following two hemorrhagic colitis outbreaks in 1982.
The initial symptoms of hemorrhagic coli-tis generally occur 12 to 60 hours after eating contaminated food, although periods of 3 to 5 days have been reported. This bacterium attaches itself to the walls of the intestine, producing a toxin that attacks the intestinal lining. Symptoms start with mild, non-bloody diarrhea that may be followed by abdominal pain and short-lived fever. During the next 24 to 48 hours, the diarrhea increases in intensity to a 4 to 10-day phase of overtly bloody diarrhea, severe abdomi-nal pain, and moderate dehydration.The destruction of E. coli O157:H7 can be accomplished by cooking ground beef to 72ºC or higher, or incorporating a procedure that kills this pathogen in the manufacture of fermented sausages or the pasteurization of apple cider.
Listeriosis Listeria monocytogenes is an especially dangerous pathogen because it can survive at refrigerated temperatures. Listeriosis causes an esti-mated 2,500 serious illnesses and 500 deaths annually). Individuals in certain high-risk groups are more likely to acquire listeriosis. Pregnant women are approximately 20 times more susceptible than other
healthy adults L. monocytogenes is an opportunistic pathogen, as it is not expected to cause severe disease in healthy individuals with strong immune systems This microorganism is a facultative gram-positive, rod-shaped, non-spore-forming microaerophilic (5 to 10% CO2) bacterium. L. monocytogenes, a ubiquitous pathogen,occurs in human carriers (ca. 10% of the population) and is found in the intestinal tracts of over 50 domestic and wild species of birds and animals, including sheep, cattle, chickens, and swine, as well as in soil and decaying vegetation. Other potential sources of this microorganism are stream water, sewage, mud, trout, crustaceans, houseflies, ticks, and the intestinal tracts of symptomatic human carriers. This pathogen has been found in most foods, from chocolate and garlic bread to diary products and meat and poultry. Elimination of Listeria is impractical and may be impossible. The critical issue is how to control its survival.The optimal temperature range for the proliferation of this microbe is 30 to 37ºC; however, growth can occur at a temperature range of 0 to 45ºC. This microorganism is considered to be a psychrotrophic pathogen, which grows well in damp environments.
L. monocytogenes is very tolerant of environ-mental stresses compared to other vegetative cells and has a high vegetative cell heat resist-ance. It grows in over 10% salt and survives in saturated salt solutions. L. monocytogenes can adhere to food con-tact surfaces by producing attachment fib-rils, with the subsequent formation of a biofilm, which impedes removal during cleaning. The attachment of Listeria to solid surfaces involves two phases. They are pri-mary attraction of the cells to the surface and firm attachment following an incubation period.
Salmonellosis
Salmonellosis is considered a food infection because it results from the ingestion of any one of numerous strains of living Salmonella organisms. These microbes grow in a 5 to 47ºC (37ºC optimal temperature) environment and produce an endotoxin (a toxin retained within the bacterial cell) that causes the illness. The usual symptoms of salmonellosis are nausea, vomiting, and diarrhea, which appear to result from the irritation of the intestinal wall by the endotoxins. Salmonellae are facultative anaerobic, gram-negative non-spore-forming, ova-shaped bacteria that primarily originate from the intestinal tract. This pathogen gen-erally grows at an optimum Aw of 0.86 in a pH range of 3.6 to 9.5 with an optimum range of 6.5 to 7.5. A salt concentration of over 2% will retard growth, but this microbe is very tolerant of freezing and drying. These bacteria may be present in the intestinal tract and other tissues of poultry and red meat animals without producing any apparent symptoms of infection in the animal. This microorganism has been an enduring prob-lem for fresh poultry and has been found on up to 70% broiler carcasses. Although Salmonella organisms can be present in skeletal tissues, the major source of the infection results from the contamination of food by the handlers during processing, through recontamination or cross-contami-nation. Salmonellae transferred by the finger-tips are capable of surviving for several hours and still contaminating food. Thermal pro-cessing conditions for the destruction of S. aureus will destroy most species of Salmo-nella. Because of the origin of these bacteria and their sensitivity to cold temperature, salmonellosis can usually be blamed on poor sanitation and temperature abuse.
Shigellosis
Shigella gastroenteritis (called shigellosis or bacillary dysentery) is an infection with an onset time of 1 to 7 days that endures 5 to 6 days. Primary symptoms vary with severe cases that may result in bloody diarrhea, mucus secretion, dehydration, fever, and chills. Death may occur among immunocompromised individuals, but the mortality rate is usually low among others. Foods most associated with shigellosis are those subjected to a large amount of handling or those contaminated with waterborne Shigella. Foods most likely to be infected with this microorganism are potato, chicken, shrimp and tuna salads, and seafood/shellfish. Most of the outbreaks have occurred in foodservice establishments such as hospital cafeterias and restaurants and are frequently attributable to ineffective hand washing after defecation.Shigella are gram-negative, non-spore-forming rods that are weakly motile and lac-tose negative with low heat resistance. Shigella are generally not hearty and lackr resistanceto environmental stresses. These facultative anaerobes grow from 6 to 48ºC with an optimum temperature of 37ºC. This microorganism is primarily of human origin and is spread to food by carriers and contaminated water. The pH range for Shigella is 4.9 to 9.3. Shigella spp. elaborate a toxin that has enterotoxic, neurotoxic, and psychotoxic activities responsible for inflammatory intestinal responses.
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