MICROBIOLOGY Manual - 2012

CHAPTER 13. PATHOGENIC MICROORGANISMS

13.4. FOOD POISONING

Food poisoning occurs after the consumption of foods in which certain microorganisms have multiplied or toxins have accumulated. Regardless of the causative agent, food poisoning shares A number of common clinical and epidemiological features: the disease is characterized by outbreaks among individuals who consumed the same food; it has a short incubation period (ranging from 2–4 hours to 48 hours); and it has an acute onset accompanied by nausea, vomiting, diarrhea, and weakness. Occasionally, Water-electrolyte balance as well as the Functions of the cardiovascular and nervous systems are disrupted. Food poisoning of microbial origin is conventionally divided into toxicoinfections and toxicosis (intoxications).

Toxicoinfections are acute intestinal diseases that arise from the consumption of foods in which massive accumulation of pathogenic microbes has occurred. In toxicoinfections, a large dose of Bacteria enters the human gastrointestinal tract, and their destruction in the Small Intestine leads to the release of a significant amount of endotoxins, which cause pathological Changes in the intestinal wall and exert a toxic effect on the Central Nervous system.

The causative agents of toxicoinfections include bacteria of the genera Salmonella, Proteus, Enterococcus, as well as the species Escherichia coli, Bacillus cereus, and Clostridium perfringens.

Genus Salmonella. The most frequent food toxicoinfections (in 96% of cases) are salmonelloses, caused by bacteria of the genus Salmonella, which belongs to the family Enterobacteriaceae. Most often, the causative agents of food toxicoinfections are S. himurium, S. enterica, and S. cholerasuis.

Salmonellae are small rods with rounded ends, up to 2 µm in length, motile (peritrichous), Gram-negative, and do not form spores or capsules. They are facultative anaerobes with an optimal growth Temperature of 37 °С. Salmonellae possess a relatively high resistance to various environmental factors. They tolerate drying and freezing well, remaining viable for several months and even 2–3 years. However, salmonellae are rapidly destroyed by high temperatures: at 70 °С in 5–10 minutes, and instantaneously upon boiling. The death of salmonellae also occurs rapidly when exposed to disinfectants.

The reservoir and source of salmonellae are infected animals (cows, sheep, pigs, horses, dogs, mice, rats, etc.). Goose and duck eggs are frequently contaminated with salmonellae. These eggs are not approved for sale and are prohibited from being consumed without thermal Processing. In the food industry, employees suffering from salmonellosis or bacterial carriers present a particular hazard. It has been established that chronic salmonella carriage is observed in 2–5% of individuals who have recovered from the disease.

Salmonellae can persist in various food products for a long time. In butter, they remain viable for 4 months at room temperature and for 9–10 months under refrigeration. In frozen egg melange at a temperature of —20 °С, salmonellae remained viable for 13 months. In salted and smoked products, these bacteria can persist for several months. In meat, fish, and dairy products, salmonellae multiply readily without altering their organoleptic properties.

The primary cause of salmonellosis is the consumption of meat and meat products, which account for up to 70–80% of all cases. Meat can be infected both during the animal's life and post-mortem. About 70% of salmonella toxicoinfection cases are caused by meat products from emergency-slaughtered animals. Infection of meat and meat products can occur through contact with dirty hands, rodents, or flies. The intensity of contamination increases sharply when meat is ground (minced meat preparation). Aspic dishes (studen) pose a certain hazard, as their preparation technology promotes salmonella contamination. Liver sausages, Blood sausages, headcheese, and navy-style pasta can also be the cause of salmonellosis outbreaks.

Milk and dairy products (cheese, sour cream, ice cream) rank second as a vehicle for transmitting the salmonellosis agent (about 10% of cases). Approximately 8–10% of salmonellosis cases are associated with the consumption of eggs, egg melange, and mayonnaise. Up to 3% of poisonings are attributed to fish products, and isolated outbreaks may be caused by the consumption of salads, vinaigrettes, and cream-filled pastries.

Genus Escherichia was first isolated from human feces in 1885 by the German scientist T. Escherich.

E. coli are small Gram-negative rods, motile, non-spore-forming, and facultative anaerobes. Escherichias are undemanding regarding nutrients and grow well on simple nutrient media. The optimal growth temperature is 37 ± 2 °С, the growth range is from 5 to 45 °С, and the optimal pH of the medium is 7.2 ± 2. Strains of E. coli inhabiting warm-blooded animals can multiply at a temperature of 42–43 °С.

Escherichia coli lacks resistance to unfavorable environmental factors and is destroyed by heating to 60 °С for 15–20 minutes, at 75 °С for 4–5 minutes, and upon exposure to a 1% phenol solution for 5–15 minutes.

E. coli is frequently detected in meat and dairy products, but it rarely causes food poisoning. This is because Escherichia coli, as a rule, does not accumulate in a product in numbers sufficient to cause poisoning. Food poisoning occurs when the concentration of E. coli Cells in a product reaches 10⁶–10⁷ per 1 g or 1 cm³ of the product.

Genus Proteus. For the first time, Proteus vulgaris was isolated from rotting meat in 1885. Currently, The Role of Proteus as a CAUSATIVE AGENT OF food toxicoinfections is recognized by the majority of researchers. Species found in food products include P. vulgaris, P. mirabilis, P. rettgeri, and P. morgana.

Proteus species are small, Gram-negative, highly motile rods that do not form spores or capsules. On solid media, they exhibit creeping growth, known as the "swarming" phenomenon. The optimal growth temperature is 25–37 °С, with a growth range of 5–43 °С. Among Proteus rods, toxigenic strains can be found that produce thermostable endotoxins, which are glucido-lipid-polypeptide complexes. Food poisoning may also be caused by the accumulation of toxic amines formed As a result of protein breakdown under the action of active proteases produced by Proteus bacteria.

The causes of food poisoning are most frequently meat and fish products (aspic dishes, cutlets, pates), as well as vinaigrettes, salads, and other culinary dishes.

Genus Enterococcus. Among enterococci, which are normal inhabitants of the human intestine, there are potentially pathogenic strains that produce enterotoxins. These include Enterococcus faecalis and E. faecium.

Enterococci are Gram-positive cocci with a diameter of 0.5–1.0 µm, arranged in pairs or chains. Strains possessing motility and synthesizing a capsule are occasionally found among enterococci. They are facultative anaerobes and grow on solid media as small, transparent, bluish colonies. On blood Agar, they may exhibit α- or β-hemolysis. The optimal growth temperature is 37 ± 2 °С, with a temperature growth range of 10–45 °С. Unlike lactic acid lactococci belonging to serological group N, enterococci belong to serological group D.

Enterococci are quite resistant to drying and chilling, and they withstand heating at 60–65 °С for 30 minutes. Consequently, they generally survive in milk pasteurized at 80–85 °С with brief holding times.

The cause of enterococcal food toxicoinfections is ready-to-eat dishes and products that have not undergone thermal processing after preparation: cutlets, meatballs, sausages (liver and blood sausages), frankfurters, boiled fish, aspic dishes, salads, vinaigrettes, milk, dairy products, creams, puddings, etc.

Bacillus cereus is a large Gram-positive rod, forms endospores, and is motile. Individual strains of this species may form a capsule. The optimal growth temperature is 30 ± 2 °С. B. cereus is an aerobic bacterium that grows on simple nutrient media and forms white colonies with jagged edges on meat-peptone agar. This species of bacteria produces an enterotoxin, exhibits hemolytic properties, produces the enzyme lecithinase, liquefies gelatin, and curdles and peptonizes milk. B. cereus spores are characterized by high thermal stability—they withstand heating at 105–125 °С for 10 minutes and can remain viable during the sterilization of milk and certain canned foods. The microbe can multiply at a sodium chloride concentration in the medium of up to 10–15% and sugar concentration of up to 30–60%.

B. cereus is a soil microbe and is therefore also found in air and water, from which it enters food products.

Foodborne toxic Infections caused by this microbe typically occur when consuming animal and plant-derived products in which the bacilli actively multiply without causing noticeable organoleptic changes. Poisoning often arises from salads, side dishes, canned plant products, and sauces where bacterial spores are introduced via flour, starch, or spices. Outbreaks have also been documented following the consumption of meat products (such as cutlets, boiled chicken, and roasted pork), broths, side dishes, confectionery, ice cream, and puddings.

Clostridium perfringens. The name of the pathogen relates to its ability to produce a large volume of gas that disrupts dense media (from Latin perfringens — breaking through, shattering).

C. perfringens is a large, Gram-positive, non-motile rod. It forms spores slowly, which are located centrally within The Cell. In the bodies of humans and animals, it forms a capsule. Although an obligate anaerobe, it can tolerate and grow in the presence of small amounts of oxygen.

The pathogen ferments almost all sugars with gas production. When grown in milk, it forms a characteristic spongy clot alongside abundant foaming. The optimal growth temperature ranges from 37–43 °C, with an optimal pH of 7.2–7.4. In food products, it multiplies at temperatures no lower than 15–20 °C. Bacteria of this species produce an enterotoxin, which is the underlying cause of toxic infections.

Spores of C. perfringens can withstand boiling for 15–90 minutes. Vegetative cells are most effectively targeted by hydrogen peroxide, standard concentrations of phenol solutions, and numerous Antibiotics effective against Gram-positive bacteria.

As a natural constituent of the normal microflora in humans and warm-blooded animals, Clostridium perfringens can contaminate Food Products and survive standard culinary processing. Poisoning is most frequently associated with dishes prepared from meat (such as cutlets or boiled meat stored at room temperature), cold meat appetizers, and meat- or offal-filled pastries. High levels of contamination by these microorganisms are frequently noted in various spices, flour, groats, and greens.

Toxicosis occurs through the consumption of food products in which microbial byproducts—toxins—have accumulated during the proliferation of microbes. According to the "Classification of Food Poisoning," this group of conditions includes bacterial toxicosis and mycotoxicosis. Bacterial toxicosis encompasses poisonings caused by the exotoxins of Staphylococcus aureus and Clostridium botulinum.

Genus Staphylococcus. Among the microorganisms responsible for foodborne toxicosis, staphylococci occupy a leading position. Staphylococci were first isolated by L. Pasteur in 1880 from human furuncle pus.

Staphylococci belong to the family Micrococcaceae and the genus Staphylococcus. These spherical cells measure 0.8–1.0 µm in diameter and arrange themselves in irregular clusters reminiscent of bunches of grapes (from Greek staphyle — grape bunch). They are non-motile, Gram-positive, and do not form spores. Strains of Staphylococcus aureus are capable of forming a delicate capsule.

They are facultative anaerobes, though they thrive better under aerobic conditions. On meat-peptone agar, staphylococci form circular colonies with smooth edges that are typically smooth, though occasionally rough. In the presence of oxygen and diffuse light, staphylococci produce pigments of varying colors: golden-yellow in S. aureus, white in S. epidermidis, and lemon-yellow in S. saprophyticus.

Staphylococci proliferate effectively on standard nutrient media at a pH of 7.2–7.4, with an optimal growth temperature of 30–37 °C and a broader growth range of 10–45 °C. They are inactivated at 70–80 °C within 20–30 minutes, and instantaneously upon boiling. The enterotoxin produced by staphylococci remains stable at 100 °C for 30 minutes. Their growth is inhibited by high concentrations of sodium chloride (> 12%) and sugar (> 60%), as well as low active acidity (pH < 4.5). Exposure to disinfectants (such as a 3% phenol solution or a 1% chloramine solution) destroys them within 15–20 minutes.

While the majority of staphylococci are saprophytic, certain species are pathogenic to humans. Staphylococcus aureus is recognized as the most pathogenic, responsible for tonsillitis, purulent-inflammatory conditions such as mastitis, Phlegmon, felon, and wound suppuration. Pathogenic staphylococci produce an array of toxins and Enzymes targeting various host cells and substrates: hemolysin (which lyses red Blood Cells), leukocidin (which destroys white blood cells), enterotoxin (which triggers food poisoning), necrotoxin (which causes tissue necrosis), coagulase (which promotes Blood Plasma clotting), fibrinolysin (which dissolves blood clots), and phosphatase, among others.

The primary source of staphylococcal infection consists of individuals with purulent Skin lesions or those harboring toxigenic staphylococci within their Upper Respiratory Tract.

Frequent causes of staphylococcal toxicosis include the consumption of milk from cows with mastitis, dairy products manufactured from pooled milk contaminated with mastitic milk (such as cottage cheese, sour cream, and cheese), and other foods where exotoxin accumulation has occurred due to the proliferation of Staphylococcus aureus. Enterotoxin accumulation peaks between 28–37 °C in dairy and meat products, side dishes, cream-filled pastries, canned fish in oil, and ready-to-eat fish and meat dishes.

Clostridium botulinum. Botulism is a severe and frequently fatal form of food poisoning resulting from the ingestion of foods containing the exotoxin of C. botulinum.

The first documented description of botulism was provided in 1817 by the German physician Kerner. The illness followed the consumption of sausage, prompting the researcher to name the affliction after "sausage poison" (derived from the Latin botulus — sausage). In Western Europe, botulism was traditionally linked to sausage consumption, in America to canned vegetables, and in Russia to red fish.

C. botulinum appears as large spore-forming rods with rounded ends, measuring (0.6–1.0) × (3–9) µm. They are Gram-positive, motile via peritrichous flagella, and non-encapsulated. Oval spores are situated subterminally, giving the microbe the distinct appearance of a tennis racket.

Spores of C. botulinum exhibit high thermoresistance, withstanding temperatures of 100 °C for 3–5 hours and 120 °C for approximately 25 minutes.

It is an obligate anaerobe. On solid media, it grows as small, transparent colonies with smooth or jagged margins. On Zeissler's sugar-blood agar, zones of hemolysis develop around the colonies of the botulinum bacillus. The optimal growth temperature is 30–40 °C, with an optimal pH of 7.2–7.4.

The botulism pathogen produces two primary types of toxins: a neurotoxin and a hemolysin. The neurotoxin is considered one of the most potent biological poisons known worldwide, with a lethal human dose of approximately 0.3 µg. Clinical manifestations of botulism include dizziness, headaches, occasional vomiting, visual impairments, mydriasis (pupillary dilation), diplopia (double Vision), paralysis of the swallowing Muscles, and Hearing loss. The mortality rate is approximately 40–60%.

The botulinum toxin is a simple protein composed exclusively of Amino Acids. It is relatively thermostable, requiring heating to 80 °C for 30 minutes or 100 °C for 15 minutes to be inactivated within a food product.

C. botulinum is widely distributed in nature and frequently isolated from soil, manure, ROOT vegetables, and the intestinal tracts of warm-blooded animals and fish.

Foods contaminated with C. botulinum may exhibit the odor of rancid butter, a stinging taste, or a loose consistency. However, these signs are inconsistent, and foods containing high concentrations of exotoxin may remain organoleptic indistinguishable from safe, wholesome products. Furthermore, because the toxin within contaminated food is sometimes distributed in localized pockets, poisoning does not necessarily affect every individual who shares the same meal.

Potential sources of poisoning include canned meats, vegetables, and fish, dry-cured and salted hams, salted fish, canned mushrooms, and the meat of chickens and ducks, among others.

To prevent botulism outbreaks in food processing facilities, strict adherence to Sanitary and hygienic regulations is mandatory. Proper technological Organization of food processing—especially concerning canning Procedures—plays a vital role in Prevention, with sterilization regime control being paramount. Salting of fish must be conducted in a strong brine solution (pickle) with a sodium chloride concentration of at least 10%. Because the botulinum pathogen is sensitive to acidic environments, The addition of acids during marinating or their natural accumulation during Fermentation effectively suppresses its proliferation.

Food poisoning can also be caused by bacteria of the species Aeromonas hydrophila, Vibrio parahaemolyticus, and certain members of the genera Citrobacter, Edwardsiella, and Pseudomonas.

Mycotoxicoses. Certain species of Molds are capable of producing toxic substances known as mycotoxins. Mycotoxins (from the Greek myces meaning fungus and toxicon meaning poison) are low-molecular-weight secondary metabolites produced by mold Fungi. They serve as natural contaminants of cereal grains, legumes, sunflower seeds, as well as fruits and vegetables. Mycotoxins can form in A wide variety of food products under the action of molds growing upon them. In addition to high toxicity, many mycotoxins exhibit mutagenic, teratogenic (fetus-damaging), hepatotoxic, and carcinogenic properties. Over 250 species of fungi are known to produce mycotoxins. Table 8 lists the most thoroughly studied mycotoxins and their producers.

Class="center">Table 8. Key mycotoxins produced by molds

Aflatoxins belong to the group of the most hazardous mycotoxins. While quite a few naturally occurring aflatoxins exist, six of them have been studied most extensively: B₁, B₂, G₁, G₂, M₁, and M₂. Acute aflatoxicosis primarily affects the liver, followed by nervous system dysfunctions accompanied by convulsions, paralysis, and ataxia. Chronic aflatoxicosis is characterized by liver damage, including The formation of adenocarcinomas in The Liver and Stomach—sometimes with Metastases in the Lungs and Kidneys—as well as fibrosarcomas. The Toxic Effect of aflatoxins stems from their interaction with DNA, RNA, and Proteins.

Patulin is the second most common mycotoxin. It is produced by the molds Penicillium patulum and Penicillium expansum. Patulin is frequently found in moldy apples, sea buckthorn, other fruits, berries, and vegetables. It exhibits strong mutagenic and carcinogenic properties and inhibits the synthesis of proteins, DNA, RNA, and enzymes that contain an SH group in their active center.

Trichothecenes. The most widespread mycotoxins in this group are produced by fungi of the genera Trichothecium, Stachybotrys, Trichoderma, and Fusarium (Fusarium sporotrichiella, Fusarium solani, Fusarium graminearum). The trichothecene group comprises over 80 mycotoxins, which are subdivided into four types: A, B, C, and D. A representative type A mycotoxin is T-2 toxin; type B is deoxynivalenol (DON); type C is roridin; and type D is crotocin.

T-2 toxin is one of the most toxic trichothecene mycotoxins. Trichothecenes inhibit Protein Synthesis in Eukaryotic cells, thereby exerting adverse effects on animals and humans that manifest as anemia, immunosuppression, hemorrhages, vomiting, mucosal necrosis, and dermatitis. They target the Hematopoietic Organs and the central nervous system, and can induce leukopenia and hemorrhagic syndrome.

Zearalenone and its derivatives. This group encompasses 15 mycotoxins. The primary producer of zearalenone is the fungus Fusarium graminearum. It is frequently detected in corn, and occasionally in wheat, barley, oats, and sorghum, as well as in oil and starch derived from zearalenone-contaminated corn.

Consumption of foods contaminated with zearalenone leads to severe Reproductive System disorders and generalized systemic poisoning.

Ochratoxin. The discovery of toxicity in the fungus Aspergillus ochraceus led to the isolation of three chemically related toxic metabolites: ochratoxins A, B, and C. Ochratoxin A is a coumarin derivative produced predominantly by A. ochraceus as well as by molds of the genus Penicillium: P. viridicatum, P. variabile, and P. cyclopium. Ochratoxins inhibit PROTEIN SYNTHESIS AND disrupt Glycogen METABOLISM.

Fumonisins. This group of mycotoxins is produced by the molds Fusarium moniliform and Fusarium proliferatum. These mycotoxins exhibit carcinogenic activity and cause liver cirrhosis. Fumonisin interferes with the synthesis of Sphingolipids, thereby disrupting lipid Metabolism in the Body.

The levels of mycotoxins—such as aflatoxin B, DON, zearalenone, T-2 toxin, patulin, and fumonisin—are regulated in food raw Materials and plant-derived food products, whereas aflatoxin M is regulated in milk and dairy products. The maximum allowable limits in food products are 0.005 mg/kg for aflatoxin B; 0.05 mg/kg for patulin; 0.1 mg/kg for T-2 toxin; 0.5 and 1.0 mg/kg for DON; 1.0 mg/kg for zearalenone; and 0.2 mg/kg for fumonisin.

Diseases caused by mycotoxins include ergotism, aflatoxicoses, and fusariotoxicoses.

Ergotism. The toxicity of moldy food products has been known for quite some time. In the early 20th century, an outbreak of disease occurred as a result of consuming bread made from flour contaminated with ergot (Claviceps purpurea). The cause of this ailment remained unknown for a long time, and it was commonly referred to as "St. Anthony's fire" or violent spasms. It is now understood that ergot mycotoxins can adversely affect the Human and Animal body.

The toxic agent for humans is the resting stage of the fungus, appearing as purplish-brown "ergot sclerotia" (horns). These sclerotia contain lysergic acid Alkaloids and clavine derivatives. These toxic compounds are heat-stable and retain their toxicity even after bread is baked. Long-term grain storage does not inactivate ergot toxins. Among these alkaloids, ergotinine is the most potent. It induces convulsions, prolonged smooth Muscle spasms, central nervous system damage, and acute gastroenteritis. In severe cases, hallucinations, mental disorders, and epileptic seizures (hence the historical term "violent spasms") are observed. Large doses of ergotinine are fatal. During recovery, patients may experience paresis (local paralysis) and muscle atrophy.

In 1938, Albert Hofmann chemically synthesized the drug LSD from the lysergic acid derivatives found in ergot, and in 1943 he discovered its hallucinogenic effects on humans.

Aflatoxicoses are alimentary diseases in birds, fish, animals, and humans associated with the ingestion of aflatoxin-contaminated feed or food products.

The first scientific investigation of mycotoxins was conducted in 1961 to determine the cause of the mass mortality of 100,000 turkey poults in Great Britain. The outbreak was caused by a mold toxin produced by Aspergillus flavus, which had entered the feed via moldy peanut meal. The isolated toxin was named aflatoxin.

Aflatoxins may be present in moldy plant-derived products (such as corn, rice, soybeans, peanuts, and sunflower seeds). In milk and meat, aflatoxins are detected when animals are fed contaminated feed. It is important to emphasize that milk pasteurization and drying do not affect the concentration of aflatoxin M₁. During cheesemaking from contaminated milk, 50% of the aflatoxin is recovered in the curd. In butter production, 10% of the aflatoxin remains in the cream and 75% in the skim milk. Cheeses and dry-cured sausages can become moldy during ripening, leading to the accumulation of mycotoxins in the product.

Aflatoxicosis can present in acute and chronic forms. The acute form is characterized by gastrointestinal tract damage, acute diarrhea, hepatic necrosis and fatty infiltration, and Kidney damage. Symptoms of poisoning also include convulsions, loss of coordination, and paresis. Aflatoxins act as hepatotoxic poisons, and chronic poisoning can lead to liver cirrhosis or primary liver Cancer.

Acute aflatoxicoses in humans are rare, as they are associated with high concentrations of aflatoxins in food (ranging from 0.2 to 2–3 mg/kg).

Fusariotoxicoses. Notable poisonings within this category include alimentary toxic aleukia and "drunken bread" poisoning.

Alimentary toxic aleukia (ATA) is a disease resulting from the consumption of food products made from grain infested with the mold fungus Fusarium sporotrichiella. This fungus proliferates on grain that has wintered in the field or been harvested late due to adverse weather conditions, as well as on grain stored under high-humidity conditions.

The illness presents similarly to a severe sore throat, accompanied by fever, hemorrhages of various localizations, and tachycardia. Pathological complications can persist for a long time (such as hepatitis, gastroenteritis, and central nervous system disorders).

"Drunken bread" poisoning. This type of fusariotoxicosis is associated with the consumption of bread made from grain infected by the fungus Fusarium graminearum. As the F. graminearum fungus multiplies on the grain, it accumulates mycotoxins, specifically glucosides and alkaloids.

This poisoning was first described in 1882 in the Russian Far East by N. A. Palchevsky under the names "drunken bread" and "poisonous barley." A similar condition occurred in 1883 in Sweden, Finland, Germany, and North America as a result of using contaminated grain imported from America.

Symptoms of poisoning include weakness, heaviness in the limbs, followed by severe headaches, dizziness, vomiting, abdominal pain, and diarrhea. In severe cases, loss of consciousness is observed. A day later, the affected individual develops a state resembling severe alcohol intoxication.