Human Gastrointestinal Disorders
CausesFrom consumption of food and water containing viable pathogenic microorganisms or their preformed toxins.From ingestion of pathogenic algae or parasites and their preformed toxins .From Other reasons Which include:Ingestion of toxins naturally present in many foods such as certain mushrooms, some sea foods.Toxins formed in some foods e.g. biological amines (histamine) in fish, cheeses, fermented meat products
The presence of toxic chemicals in contaminated food and water (heavy metals and pesticides).Allergy to some normal components of a food(allergy to gluten in cereal).Genetic inability to metabolize normal food components9lactase enzyme deficiency).Nutritional disorders(rickets due Ca deficiency).Indigestion from overeating.**The incidence of foodborne diseases of microbial origin is higher than that for all other causes combined.
Types of Microbial Foodborne Diseases
Foodborne diseases in humans result from the consumption of either food and water contaminated with viable pathogenic bacterial cells(or spores in case of infant botulism) or food containing toxins produced by toxigenic bacteria and molds. On the basis of mode of illness, these are divided intothree groups:Intoxication or poisoningInfectionToxicoinfection
IntoxicationIllness occurs as a consequence of ingesting a preformed bacterial or mold toxin, a toxin has to be present in the contaminated food.Staphyloccocusaureusfood poisoning is an example of this type.InfectionIllness occurs as a result of the consumption of food and water contaminated withenteropathogenicbacteria or viruses. Viable Microorganisms have the potential to establish and multiply in the digestive tract to cause the illness. Salmonellosis and hepatitis A areexamlpes.ToxicoinfectionIllness occurs after ingesting large number of viable pathogenic bacteria, the bacterial cells eithersporulateor die and release toxins.Clostridiumperfringensgastroenteritis is an example.
Predominant Bacterial and Viral pathogens Associated with Foodborne Diseases
StaphylococcusaureusClostridium botulinumSalmonellsSpp.ShigellaSpp.Escherichia coliCampylobacter Spp.ClostridiumperfringensBacillus cereusHepatitis A virusNorwalk-like virus
Predominant Food Types Associated with Foodborne Diseases of Bacterial and Viral Origin
*Meat Products*Fish Products*egg Products*Dairy Products*Salads*Baked Food*Fruits and vegetables*Mushrooms*Ethnic Food*Multiple Foods*Unknown Foods
Predominant Contributing Factors Associated with Foodborne Disease Outbreaks
Improper Holding Temperature (temperature abuse)Poor Personal hygieneInadequate CookingContaminated EquipmentFood From Unsafe SourcesOthers
Human Factors In foodborne Disease Symptoms
When a group of people consumes food contaminated with live cells of pathogens or their toxins, all the members might not develop disease symptoms.Not all infected people show the same symptoms or severity of a symptom. This is probably due to the difference in resistance among individuals.Infants and old, sick, andimmunodeficientpeople are more susceptible than healthy ones.The chance of developing disease symptoms is directly related to the amount of a contaminated food consumed, number of viable cells, amount of toxin and virulence.Consumption of 10 viable cells ofE. coli0157:H7 can cause disease, while one million cells ofYersiniaenterocoliticaare needed to cause disease.
Foodborne intoxication or food poisoning of microbial origin occurs by ingesting a food containing a preformed toxin.General characteristics of food poisoningThe toxin is produced by a pathogen while growing in a food.A toxin can be heat labile or heat stable.Ingestion of a food containing active toxin is necessary for poisoning(except for infant botulism, in which viable spores need to be ingested).Symptoms generally occur quickly(in about 30 min).Symptoms differ with type of toxin(enterotoxins produce gastric symptoms and neurotoxins produce neurological symptoms).
S.aureusalong with many other staphylococci, are naturally present in nose, throat, skin, and hair(feathers) of healthy humans, animals, and birds.S.aureuscan be present in infections, such as cuts in skin and abscesses in humans, animals and birds, and cuts in hands and facial-erupted acne in humans.Food contamination generally occurs from these sources.
Toxins and toxin Production
Enterotoxigenicstrains ofS.aureusproduce seven different enterotoxins; A, B, C1, C2, C3, D, EThey are serologically distinct heat stable proteins of molecular weight 26-30kDa and differ in toxicity.Normal temperature and time used to process or cook foods do not destroy the potency of the toxins.Under optimum conditions of growth, toxins can be detected when a population has reached over a few million per gram or milliliter of food and within four hours.
Disease and Symptoms
A healthy adult has to consume 30 g or ml of a food containing 100-200 ng toxins produced by 1-2 million cells/g or ml; infants and old and sick individuals need lesser amounts.The symptoms occur within 2-4 hours and are directly related to the potency and amounts of toxin ingested and an individual resistance.The disease lasts for 1-2 days and is rarely fatal.The primary symptoms , from stimulation of the autonomic nervous system by the toxins, are salivation, nausea, vomiting, abdominal cramps and diarrhea.Secondary symptoms are sweating, chills, headache and dehydration.
Food types involved in Staphylococcal food poisoning:PorkBakery productsTurkeyChickenEggsFishDairy productsFruitsEthnic foods
Food or vomit samples are analyzed for the presence ofenterotoxigenicS.aureuscells and enterotoxins.Biological testing for enterotoxinAnimals(cat, monkeys, dogs) are given the enterotoxin preparation orally or it is injectedintraperitoneallyor intravenously. Vomiting symptoms by the test animals is a positive indication of the presence of staphylococcal enterotoxin.Serological MethodsThe enterotoxin are purified and examined by one of the several immunological methodse.gELISA.
Botulism results following consumption of food containing the potent toxin botulin of the anaerobic bacteriaClostridium botulinum.It is a neurotoxin and produces neurological symptoms along with some gastric symptoms.Unless prompt treatment is administered, it is quit fatal.Infant botulism occurs when an infant ingestsC.botulinumspores, which germinate, grow and produce toxins in the GIT and cause specific symptoms.
Spores ofC. botulinumare widely distributed in soil, sediments of lakes, plants, intestinal contents of animals and fishes.Fruits and vegetables can be contaminated with spores from soil, fishes from water and sediments.The toxins are neurotoxic proteins, only small amount of toxin is required to produce the symptoms and cause death.The toxin is absorbed from intestine and spread via blood to the peripheral nerves.The toxin blocks signal transfers, irreversibly causing paralysis of all involuntary muscles
Disease and Symptoms
Botulism is caused by ingestion of the neurotoxin botulin formed in food.Neurological symptoms develop within a short time, especially if the amount of botulin consumed is high.A very small amount(1ng/kg body weight) is necessary for severe symptoms and even death.Neurological symptoms include blurred or double vision, difficulty in swallowing, breathing and speaking, dryness of the mouth and paralysis of different involuntary muscles. Death usually results from respiratory failure.The toxins are antigenic; thus antitoxins are available.Soon after symptoms antitoxin should be administered, it should not be delayed.
Food types involved in botulism outbreaksBeef stewChickenDairy productsFish Fruits and vegetablesMushroomsPorkTurkey
Prevention of Botulism
Use of proper temperature and time in home canning of low acid products.Strict regulations for commercial canning.Some foods (e.gfish) should be properly and uniformly cooked at high temperatures.Suspected foods should be properly heated before consumption, but it is better not to eat them.The presence of toxin in food is tested by injecting a food extractintraperitoneallyinto mice, development of neurological symptoms and death in 92 hours suggest the presence of toxin.
Many strains of molds, while growing in a suitable environment(including foods), produce metabolites that are toxic to humans, animals and birds, and are grouped asmycotoxins.Consumption of foods containingmycotoxinscausesmycotoxicosis.They are secondary metabolites and not proteins or enteric toxins.Many are carcinogens.Recently, thousands of turkeys died from liver necrosis in England following feeding peanut meal in whichAspergillusflavusgrew and produced the toxinaflatoxin.
Toxigenic species and strains of molds from many genera are known to producemycotoxins.Aspergillusflavus……………..aflatoxinAspergillusnodulans……………sterigmatocystinPenicilliumviridicatum……….ochratoxinPenicilliumpatulum………….patulinPenicelliumroquefortii………..roquefortinClavicepspurpurea…………………….ergotoxinMolds grow best in humid ,warm environment, they are aerobic, they can grow at low temperature and lowpH.Spores are present in soil, dust and the environment.
The growth of toxigenic mold strains and the presence of specificmycotoxinshave been detected in many foods:Corn, Wheat, rice, beans, peanuts, bread, cheeses, spices, cotton seeds and spaghetti.Prevention of humanmycotoxicosisis by reduction of food contamination by molds.Anaerobic packaging, reducing Aw, freezing and the use of specific preservatives.Mycotoxinscan be detected by solvent extraction of foods then applying thin layer chromatography for the extract. Mass spectral methods are also used to identify specificmycotoxin.