Bacteria are a member of a large group of unicellular microorganisms – some of which can cause human disease. Although most bacteria are harmless or often beneficial, some bacteria are pathogenic, or those that can pose a threat to human health or cause illness.
Bacteria and viruses are responsible for most foodborne illnesses and are the biggest threat to food safety.
Bacteria grow more favorably in foods that are warm, moist, protein-rich, and low in acid. Under the right conditions, bacteria can double every 10 to 30 minutes. A single bacterium can become billions in 10 to 12 hours. Bacteria grow fastest in the temperature range between 40°F and 140°F, which is known as the Temperature Danger Zone.
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Most Common Types of Pathogenic Food Bacteria
Bacteria are a category of food hazards called biological food hazards – or infectious microorganisms that are capable of causing human disease – including bacteria, viruses, and parasites.
More than 90 percent of the cases of food illness are caused by a few types of pathogenic bacteria:
- Bacillus cereus – A toxin-producing bacteria that is one of the most common causes of food illness. However, the vast majority of cases go unreported, because the symptoms are generally mild and short-lived (up to 24 hours) and subside on their own. The bacteria are present in foods (particularly pasta, rice, as well as sauces and soups) and can multiply quickly at room temperature. If cooked food is allowed to cool, slowly the spores can germinate and reheating or lightly cooking the food will not destroy this toxin.
- Campylobacter – A bacteria causing food illness associated with eating raw or undercooked poultry or from other foods contaminated by raw poultry. Symptoms include diarrhea (often bloody), fever, and abdominal cramps accompanied with nausea and vomiting. Causes an estimated 1.3 million illnesses each year.
- Clostridium perfringens – A spore-forming bacterium found naturally in many environmental sources, in the intestines of humans and animals, and on beef, poultry, gravies, and dried or precooked foods. Illness commonly occurs when cooked food contaminated with the bacteria is left out at incorrect temperatures, which allows rapid multiplication and results in toxin production. Symptoms are mild and include diarrhea and abdominal cramps (not fever or vomiting).
- Escherichia coli – Commonly referred to as E. coli, they are bacteria commonly found in the digestive tracts of animals and humans, where they assist with normal digestive processes. While some strains produce toxins that are responsible for gastroenteritis, others are responsible for urinary tract infections and respiratory illness. Symptoms include abdominal cramps and diarrhea, which may be bloody. Fever and vomiting may also occur.
- Listeria monocytogenes – Also referred to as Listeria, this bacterium bacteria is found in the soil and water and in some animals, including poultry and cattle. It can also be present in unpasteurized (raw) milk and dairy products. Pasteurization, cooking, and most disinfecting agents kill L. monocytogenes. Symptoms include fever and chills, headache, upset stomach and vomiting. Treatment is with antibiotics. Unlike most bacteria, L. monocytogenes can grow and multiply at low temperatures, making the bacteria a potential problem even in properly refrigerated food. Compared to other foodborne illnesses, listeriosis is rare but very serious. Even with adequate antibiotic treatment, the disease has a high mortality rate of 20 to 30 percent. Over 90 percent of people with listeriosis are hospitalized.
- Salmonella – Bacteria that are commonly found in the digestive tracts of animals and humans and are shed through feces. Salmonella infection is usually caused by eating raw or undercooked meat, poultry, eggs or egg products. Symptoms are generally typical of gastroenteritis (diarrhea, vomiting, abdominal pain) along with fever, chills, and headache.
- Shigella – Genetically closely related to E. coli, Shigella causes disease in humans and primates, but not in other mammals. Infection is cause by consuming water or food supplies that been contaminated with feces from humans or animals. Also, from touching the mouth after caring for an infected person or changing the diaper of an infected child. Gastroenteritis – diarrhea, fever, and stomach cramps start a day or two after they are exposed to the bacteria.
- Staphylococcus aureus – Also referred to as “Staph”, this type of bacteria is commonly found on the skin and hair as well as in the noses and throats of humans and animals. People who carry Staph can contaminate food if they don’t wash their hands before touching it. A staph infection in food usually doesn’t cause a fever. Signs and symptoms you can expect with this type of Staph infection include nausea and vomiting, diarrhea, and dehydration. Although most Staph infections from food are not serious, the bacteria can cause serious infections when entering the bloodstream.
- Vibrio parahaemolyticus – Commonly called Vibrio, are bacteria that occur naturally in warm coastal areas, such as the Gulf of Mexico. These bacteria are found in higher concentrations in the summer months when water gets warmer and and most commonly causes gastroenteritis. A Vibrio infection can be acquired by eating raw or undercooked shellfish or drinking contaminated water. Eating raw oysters is the most common way the infection is spread as the organism naturally lives in the warm tidal waters where oysters grow. Eating raw or undercooked fish and crustaceans, such as crabs and lobsters, has also been associated with foodborne outbreaks of this infection. Symptoms are generally typical of gastroenteritis (diarrhea, vomiting, abdominal pain) along with fever and headache.
- Yersinia enterocolitica – A bacterial infection caused most often by eating contaminated food, especially raw or inadequately cooked pork products. Drinking contaminated unpasteurized milk or untreated water can also transmit the infection. The bacteria causes a condition called enterocolitis, which is an inflammation of the small intestine and colon that occurs, but also symptoms such as diarrhea and a fever, mostly in young children.
- FoodSafety.gov – Bacteria and Viruses
- The National Institute of Diabetes and Digestive and Kidney Diseases Health Information Center
- CDC – Food Safety
- U.S. FDA – Foodborne Illnesses
- U.S. FDA – Foodborne Pathogens
- U.S. National Library of Medicine – Medline Plus – Bacterial Infections