Thousands of different types of bacteria exist naturally in our environment. Some are necessary and quite healthy, like probiotics that support digestive health. Others, however, like the ones you’ll read about below, can cause serious disease.

The number of bacteria that can cause illness in humans is only a small fraction of those that exist. So while it’s not necessary, or even possible, to avoid all bacteria, you should be aware of these toxic varieties, and how to keep yourself and your family safe.

Raw shellfish like oysters can contain Vibrio, bacteria that can cause diarrhea, abdominal cramping and headache.

1. Staphylococcus Aureus

Staphylococcus aureus bacteria are present in the nasal passages, throats, hair and skin of 50 percent of healthy people, according to the U.S. Food and Drug Administration (FDA). If concentrated in large quantities in foods, however, it can cause food poisoning that results in nausea, vomiting and abdominal cramping.

Foods that are at risk of contamination by Staphylococcus aureus include dairy, meats, creamy salads (egg salad, chicken salad, etc.), cream-filled pastries and sandwich fillings. Food handlers are the main cause of contamination. Although food poisoning can be serious, staphylococcal food poisoning usually resolves in two days.

The Staphylococcus aureus bacteria can also cause a much more serious problem, generically known as staph infections. Staph infections occur when the bacteria enter the skin via a puncture or cut. It can also be passed on contaminated surfaces, through the air and from person to person.

Staph bacteria can cause a number of infections, including folliculitis, boils, scalded skin syndrome, impetigo, toxic shock syndrome, and cellulites.

Now, a drug-resistant form of the bacteria, Methicillin-resistant Staphylococcus aureus (MRSA), is showing up in increasing numbers in the nation’s hospitals and intensive care units. Worse still, a particularly virulent strain, known as the community strain, is now able to infect otherwise healthy people.

“Unlike traditional MRSA the community strain is very fit — it causes infection in healthy people,” said Centers for Disease Control and Prevention (CDC) epidemiologist Dr. Monina Klevens. “When it is introduced into a hospital, where ill patients are more vulnerable to infection, it has the potential to cause significant morbidity and mortality.”

What can you do? Wash your hands frequently (including under your nails), bathe daily and keep any cuts clean and well covered. Also, keep foods hot or refrigerated until serving.

2. Vibrio

Eating food infected with Vibrio causes diarrhea, abdominal cramping, nausea and headache. In people with weakened immune systems, certain varieties of Vibrio can infect the bloodstream and be life-threatening.

“Humans become infected when they eat raw or undercooked shellfish. Each year in the United States, Vibrio cause an estimated 8,000 infections and 50 deaths,” said Dr. Nicholas A. Daniels of the University of California, San Francisco. “Shellfish, particularly oysters since they are filter-feeders, concentrate the bacteria in their tissues.”

What can you do? Only eat shellfish, such as oysters, that has been thoroughly cooked, particularly in the warm-weather months, when related infections are more common. The bacteria also exist in seawater and can infect an open wound while you’re swimming.

3. Listeria monocytogenes

Eating food contaminated with listeria bacteria can cause an infection called listeriosis, along with meningitis, encephalitis and intrauterine infections. According to the CDC, an estimated 2,500 persons become seriously ill with listeriosis each year and, of these, 500 die.

While healthy people may not experience any symptoms from ingesting listeria, pregnant women, newborns and those with weakened immune systems can become seriously ill. In pregnant women, the infection may cause a flu-like illness, however can lead to miscarriage, stillbirth, premature delivery or infection of the newborn.

Listeria is found in soil and water, and therefore can contaminate raw foods of all kinds, including fruits, vegetables, meats, seafood and dairy products. It can also contaminate soft cheeses and cooked meats like hot dogs and deli meats during packaging.

What can you do? Avoid eating raw or undercooked meats and dairy and wash all fruits and vegetables thoroughly before eating. Also wash your hands, cutting boards and counter surfaces thoroughly after handling uncooked foods. Pregnant women and others at high risk may also want to avoid:

  • Hot dogs and deli meats, unless they’re reheated until steaming hot.
  • Getting fluid from hot dog and lunchmeat packages on other foods, utensils, etc.
  • Soft cheeses such as feta, Brie, Camembert, blue-veined cheeses, Mexican-style cheeses and Panela (unless the label states they are made from pasteurized milk; though pasteurization can kill nutritional value, its benefit is the elimination of bacteria such as this)
  • Refrigerated pâtés, meat spreads and smoked seafood (unless it is part of a cooked dish).

4. Clostridium botulinum

Clostridium botulinum bacteria is a nerve toxin that can cause botulism, a serious paralytic illness. In the United States, about 110 cases of botulism are reported each year, according to the CDC. Of these, approximately 25 percent are food-borne, 72 percent are infant botulism, and the rest are wound botulism.

Food-borne botulism is caused by eating foods that are contaminated with the botulism toxin. Wound botulism occurs when a wound is infected with the Clostridium bacteria and infant botulism is caused by consuming spores of the bacteria, which then grow in the intestines and release toxins.

Botulism symptoms include double or blurred vision, drooping eyelids, slurred speech, difficulty swallowing, dry mouth, and muscle weakness. In infants, symptoms may include lethargy, constipation, a weak cry and poor muscle tone. If left untreated, the symptoms will lead to paralysis of the arms, legs, trunk and respiratory muscles.

Because hot dogs can become contaminated with listeria — bacteria that can cause miscarriage and stillbirth — during packaging, pregnant women should avoid them unless they’re heated until steaming hot.

What can you do? Home-canned foods, particularly those with low acid content such as asparagus, green beans, beets and corn, are often sources of botulism. If you can foods at home, be sure to strictly follow the proper hygiene procedures.

Other outbreaks have been found in processed foods including chopped garlic in oil, fermented fish and baked potatoes wrapped in aluminum foil. If you have herbs in oil, keep them refrigerated, and keep potatoes baked in aluminum foil hot until eaten or refrigerated.

Honey can contain spores of the Clostridium bacteria, so avoid giving honey to children less than 1 year old. Wound botulism can be prevented by seeking medical attention for infected wounds and not using illegal drugs that are injected with a needle.

5. Escherichia coli (E. coli)

There are hundreds of strains of E. coli bacteria, most of which exist harmlessly in humans’ intestines. However, certain strains are toxic and produce a serious infection that causes bloody diarrhea and sometimes kidney failure.

The CDC estimates that 73,000 cases of infection and 61 deaths occur from E. coli infection in the United States each year. Most infections are related to eating undercooked ground beef.

What can you do? You can become infected with E. coli by eating contaminated food, swimming in or drinking water that’s contaminated by sewage or by picking it up from personal contact, such as in families and day care centers. To reduce your risk of E. coli:

  • Only eat ground beef that has been thoroughly cooked
  • Wash fruits and vegetables thoroughly before eating
  • Avoid drinking unpasteurized milk if you can’t confirm the cows from which it came are healthy
  • Wash your hands frequently
  • If your child is in a day care center, be sure that the employees wash their hands after changing diapers, and that children wash their hands after using the bathroom

6. Legionella pneumophila

This bacteria leads to an infection called legionellosis. There are two forms of legionellosis:

  • Legionnaires’ disease: the severe form of the infection, which includes pneumonia. Between 8,000 and 18,000 people are hospitalized with Legionnaires’ disease in the United States each year, according to the CDC.
  • Pontiac fever: a milder illness. Symptoms, which include fever, headaches and muscle aches, go away without treatment.

Legionella bacteria are found in water, particularly warm water such as is found in hot tubs, cooling towers, hot water tanks, large plumbing systems and parts of air-conditioning systems in large buildings.

What can you do? You can become infected with Legionnaires’ disease by breathing in mist from water that is contaminated. More common sources include whirlpool spas that are not properly cleaned, and contaminated water used for drinking or bathing on cruise ships or in hotels.

Sources

Science Daily: Drug-resistant Bacteria Patterns in Intensive Care Units Changing Nationally

Journal of the American Medical Association, 2000 Sep 27;284(12):1541-5

CDC: Division of Bacterial and Mycotic Diseases