Food Poisoning: Definition, Causative Agents

Foodborne illness, also known as “foodborne disease,” “foodborne infection,” or “food poisoning, is an important public health burden worldwide. There are an estimated 250 pathogens that can cause foodborne-related illnesses. Centre for Disease Control (CDC), USA, has reported 31 known foodborne illness agents; the rest are called “unspecified agents.”

Foodborne illness is two or more cases of similar illnesses resulting from ingesting a common food. It can result from consuming foods contaminated with various pathogens. Usually, bacteria are the primary pathogen, followed by viruses, then parasites. However, organisms’ natural or manufactured chemicals and toxins can also cause foodborne illnesses.

When the performed toxins are responsible for good poisoning, symptoms appear within 1 to 6 hours of ingestion. Symptoms of food poisoning include stomach upset, abdominal cramps, nausea and vomiting, diarrhea, fever, and dehydration. Symptoms may range from mild illness to severe disease.

Food Poisoning
Food Poisoning

Foodborne Intoxications vs. Foodborne Infections

The ingestion of toxins causes foodborne intoxications, natural or preformed, bacterial or chemical, and the incubation period ranges from minutes to hours.  Bacillus Cereus, Clostridium botulinum, Staphylococcus aureus are the common causes of foodborne intoxication.

Live bacteria, viruses, or parasites are responsible for foodborne infections. They invade and multiply in the lining of the intestine and the incubation period varies from hours to days. Campylobacter jejuni, Listeria monocytogenes, and Escherichia coli 0157:H7 are the major causes of foodborne infections.

MNEMONICS: “Eating Contaminated Stuff Causes Very Big Smelly Vomit”

MnemonicsOrganismsSource
EatingE. coli O157-H7undercooked meat, esp. hamburgers
ContaminatedClostridium botulinumImproperly canned vegetables and smoked fish
StuffSalmonella spppoultry, meat, eggs
CausesClostridium perfringensreheated meat
VeryVibrio parahaemolyticusseafood
Big/BadBacillus cereusreheated rice
SmellyStaphylococcus aureusmeats, mayo, custard
VomitVibrio vulnificusSeafood

Common pathogens causing food-borne illness are:

Bacillus cereus

Ingestion of food contaminated with Bacillus cereus or toxins produced by this organism is responsible for foodborne illness. The spore of Bacillus cereus is relatively heat resistant and survives the steaming and rapid frying of rice. The spores germinate when rice is kept warm for many hours (e.g., reheated fried rice).

Bacillus cereus produces enterotoxins. It causes food poisoning of two types: diarrheal type, characterized by a long incubation period (18 hours), abdominal pain and watery diarrhea, and emetic type, with a short incubation period of 4 hours, and manifested as profuse vomiting. Emetic type resembles staphylococcal food poisoning, whereas diarrheal type resembles clostridial gastroenteritis.

Campylobacter jejuni

Campylobacter jejuni is the world’s most common bacterial cause of human gastroenteritis. People acquire this infection after consuming food and water contaminated with animal feces. As this organism is commonly found in domestic animals such as cattle and chickens, consuming unpasteurized milk or raw or improperly poultry or meat predisposes this infection. Dogs are also the reservoir of Campylobacter, so contact or playing with puppies with diarrhea is a common source of infection for children.

Proper cooking and following food hygiene while preparing food help to prevent Campylobacter infections. Proper cooking of food kills Campylobacter, so it is the best method of eliminating campylobacter from contaminated foods.

Clostridium perfringens

Clostridium perfringens, the etiological agents of gas gangrene (myonecrosis), also causes food poisoning if people acquire this organism via ingestion.  Spores of this organism are found abundantly in soil and are extremely heat resistant, which can even survive cooking.  

Consumption of improperly cooked food especially heated meat dishes, predispose to food poisoning. Certain strains of Clostridium perfringens produce an enterotoxin that causes watery diarrhea. This enterotoxin acts as a superantigen similar to the enterotoxin of S. aureus.

Clostridium botulinum

Exotoxin produced by Clostridium botulinum in the contaminated canned food causes botulism. Clostridium botulinum spores are widespread in soil and can contaminate meat and vegetables.  

The highest risk foods are smoked fish and alkaline vegetables such as green beans, peppers, and mushrooms. Spores survive and germinate in the anaerobic environment when these foods are canned or vacuum-packed without adequate sterilization. Clostridium botulinum produces toxins in this canned food, and people may inadvertently ingest toxins while consuming such foods.  

Simple precautions such as inspection of canned foods can prevent you from eating contaminated foods. Do not buy or use swollen cans. Swollen cans result from proteolytic degradation of foods by Clostridium, which causes gas formation. Proper sterilization of all canned and vacuum-packed foods and sufficient cooking of foods can prevent food poisoning caused by Clostridium botulinum. The botulinum toxin is relatively heat-labile and is inactivated by boiling for several minutes.

E.coli O157:H7

Enterohemorrhagic E. coli O157: H7 cause food-borne outbreaks associated with eating undercooked meat, especially hamburgers, in fast-food restaurants.

Cattle are the main reservoir of E. coli O157:H7 strain. Bacteria in cattle feces are ingested in undercooked hamburgers.  E. coli O157:H7 strain produces an exotoxin called Shiga toxin and causes bloody diarrhea. It can cause hemorrhagic colitis and hemolytic uremic syndrome (HUS).

Listeria monocytogenes

Listeria monocytogenes causes listeriosis, a food-borne illness that can have severe consequences for children, the elderly, and pregnant women. Outbreaks of listeria infections are associated with eating unpasteurized cheese and delicatessen meats and are the major cause of concern for food industries. Contaminated dairy products, undercooked meats such as chicken, and hot dogs can also cause, cause outbreaks. 

Salmonella Typhimurium and S. Enteritidis

Salmonella is one of the US’s most common causes of bacterial enterocolitis. Nontyphoidal species of Salmonella are mainly responsible for causing diarrhea, while typhoidal species (S. typhi and S. paratyphi) cause enteric fever.

People acquire this infection by ingesting food and water contaminated with the feces of humans and animals. The most frequent source of infection is poultry and eggs. Inadequately cooked meat products such as hot dogs and improper handling of foods by chronic carriers also cause significant outbreaks.

Shigella spp

Shigellosis is also known as bacillary dysentery. Most cases are caused by Shigella sonnei. However, S. dysenteriae, S. flexneri, and S. boydii can also cause foodborne illnesses.

Staphylococcus aureus

Staphylococcus aureus is one of the leading causes of food poisoning, characterized by prominent vomiting and watery diarrhea. Heat-resistant preformed enterotoxin of S. aureus in food is responsible for food poisoning, and symptoms usually appear within 1 to 6 hours after ingesting contaminated foods.

This enterotoxin is resistant to stomach acid and enzymes in the stomach and jejunum. There are six immunologic types of enterotoxin, types A-F. Enterotoxin of S. aureus acts as a superantigen within the gastrointestinal tract. 

Vibrio cholerae

The cholera toxin produced by Vibrio cholerae is an enterotoxin responsible for profuse watery diarrhea (rice watery stools).

Yersinia enterocolitica

Yersinia enterocolitica causes enterocolitis. People acquire infection with this organism by consuming food or water contaminated with excreta of domestic animals such as cattle, dogs, and cats.

Parasites

  1. Toxoplasma gondii: Toxoplasmosis is caused by an intracellular protozoan, Toxoplasma gondii, which can infect all species of mammals, including humans
  2. Cryptosporidium
  3. Cyclospora

Virus

  1. Adenovirus
  2. Rotavirus
  3. Calciviruses (Better known as Norwalk virus)
  4. Norwalk-like virus (or Norovirus)

Acharya Tankeshwar

Hello, thank you for visiting my blog. I am Tankeshwar Acharya. Blogging is my passion. As an asst. professor, I am teaching microbiology and immunology to medical and nursing students at PAHS, Nepal. I have been working as a microbiologist at Patan hospital for more than 10 years.

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