Microbial Foodborne Diseases

Human Gastrointestinal DisordersCauses • From 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 into three 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. Staphyloccocus aureus food poisoning is an

example of this type .InfectionIllness occurs as a result of the consumption of food and water contaminated with enteropathogenic bacteria or viruses. Viable Microorganisms have the potential to establish and multiply in the digestive tract to cause the illness. Salmonellosis and hepatitis A are examlpes.

ToxicoinfectionIllness occurs after ingesting large number of viable pathogenic bacteria, the bacterial cells either sporulate or die and release

toxins. Clostridium perfringens gastroenteritis is an example .

Predominant Bacterial and Viral pathogens Associated with Foodborne Diseases

•Staphylococcus aureusClostridium botulinumSalmonells Spp.Shigella Spp.

Escherichia coliCampylobacter Spp.

Clostridium perfringensBacillus cereus

Hepatitis 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 hygiene• Inadequate Cooking • Contaminated Equipment• Food From Unsafe Sources • Others

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, and immunodeficient people 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 of E. coli 0157:H7 can cause disease, while one million cells of Yersinia enterocolitica are needed to cause

disease .

Foodborne IntoxicationFoodborne intoxication or food poisoning of microbial origin occurs by ingesting a food containing a preformed toxin.

General characteristics of food poisoning The 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).

Staphylococcal IntoxicationS. aureus along with many other staphylococci, are naturally present in nose, throat, skin, and hair(feathers) of healthy humans, animals, and

birds .S. aureus can 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 ProductionEnterotoxigenic strains of S.aureus produce seven different enterotoxins; A, B, C1, C2, C3, D, E

They 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 SymptomsA 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 AssociationFood types involved in Staphylococcal food poisoning :

Pork Bakery productsTurkeyChickenEggsFishDairy productsFruits

Ethnic foods

Identification MethodsFood or vomit samples are analyzed for the presence of

enterotoxigenic S. aureus cells and enterotoxins .Biological testing for enterotoxin

Animals(cat, monkeys, dogs) are given the enterotoxin preparation orally or it is injected intraperitoneally or 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 methods e.g ELISA .

BotulismBotulism results following consumption of food containing the potent toxin botulin of the anaerobic bacteria Clostridium 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 ingests C.botulinum spores, which germinate, grow and produce toxins in the GIT and cause specific symptoms.

ToxinSpores of C. botulinum are 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 SymptomsBotulism 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 AssociationFood types involved in botulism outbreaks

Beef stewChickenDairy productsFish Fruits and vegetablesMushroomsPorkTurkey

Prevention of BotulismUse of proper temperature and time in home canning of low acid products.Strict regulations for commercial canning .

Some foods (e.g fish) 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 extract intraperitoneally into mice, development of neurological symptoms and death in 92 hours suggest the presence of toxin.

MycotoxicosisMany strains of molds, while growing in a suitable environment(including foods), produce metabolites that are toxic to humans, animals and birds, and are grouped

as mycotoxins .Consumption of foods containing mycotoxins causes mycotoxicosis.

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 which Aspergillus flavus grew and produced the toxin aflatoxin.

OrganismsToxigenic species and strains of molds from many genera

are known to produce mycotoxins.Aspergillus flavus……………..aflatoxinAspergillus nodulans……………sterigmatocystinPenicillium viridicatum……….ochratoxinPenicillium patulum………….patulinPenicellium roquefortii………..roquefortinClaviceps purpurea…………………….ergotoxinMolds grow best in humid ,warm environment, they are aerobic, they can grow at low temperature and low pH.Spores are present in soil, dust and the environment.

Food AssociationThe growth of toxigenic mold strains and the presence of specific mycotoxins have been detected in many foods:Corn, Wheat, rice, beans, peanuts, bread, cheeses, spices, cotton seeds and spaghetti.Prevention of human mycotoxicosis is by reduction of food contamination by molds.Anaerobic packaging, reducing Aw, freezing and the use of specific preservatives.Mycotoxins can be detected by solvent extraction of foods then applying thin layer chromatography for the extract. Mass spectral methods are also used to identify specific mycotoxin.