Bacterial Food Intoxications

Food intoxication or poisoning occurs when a food is consumed that contains a toxin produced by microorganisms. Bacteria that may cause food intoxication include Staphylococcus aureus, Clostridium perfringens, Clostridium botulinum, and Bacillus cereus.

Staphylococcus aureus

A major cause of foodborne illness, Staphylococcus aureus is ubiquitous. Up to half of all healthy humans carry it, and it is a common cause of sinus infections and infected pimples and boils. It lives in the throat and nasal passages and in small cuts, so it is easily transmitted to foods through sneezing, coughing, and hand contact.

Staphylococcus aureus causes a violent flu-like illness, but without fever or fatality. Symptoms appear anywhere from 30 minutes to 8 hours after ingestion of the toxin and last one or two days.

Foods that are particularly susceptible to Staphylococcus contamination are protein-carbohydrate combination foods left at room temperature long enough for the bacteria to grow and produce their toxin. Cream fillings and custards serve as a fine growth medium for Staphylococcus aureus if contaminated after cooking and stored at inadequate temperatures. Mayonnaise-based salads, especially those containing eggs or homemade mayonnaise, are susceptible to contamination when held at room temperature for extended periods.

Clostridium perfringens

This pathogen is an anaerobic bacteria, most often found in meats or meat dishes. Contamination usually occurs when such dishes are left out at room temperature, precooked and inadequately reheated, cooled too slowly after cooking, or kept on a steam table below 140°F (60°C). Symptoms of infection include abdominal cramps and diarrhea, which appear 8 to 24 hours after ingestion and usually last about 12 hours.

Clostridium botulinum

The Clostridium botulinum toxin causes botulism, one of the deadliest, but fortunately rarest, forms of foodborne illness. Less than a half cup of botulinum toxin is enough to poison every person on earth. Medical advances, including the development of an antitoxin, have contributed to reducing the death rate from botulism to less than 2 percent.

There are two major types of botulism: conventional and infant. In conventional botulism, the toxin paralyzes the nervous system, which prevents breathing and causes suffocation. Symptoms include blurred or double vision; difficulty swallowing, speaking, and breathing; and respiratory paralysis. Nausea, diarrhea, and vomiting may also be present. Ingesting even the smallest bit of toxin can cause symptoms to occur within 12 to 36 hours. The antitoxin has helped prevent deaths, but the resultant nerve damage may be permanent.

C. botulinum is common in the soil. Because it is an anaerobic organism, it grows well in sealed cans. It does not grow in high-acid foods (pH < 4.5) such as tomatoes, so low-acid canned foods are usually responsible for poisoning. Cans that are dented, have leaky seals, or bulge (indicating the presence of the gas produced by the bacteria) should be discarded. A foul odor or milky liquid in any can is also a sign of contamination. Food prepared at home, especially improperly home-canned food, is responsible for most of the conventional botulism outbreaks. Infant botulism can be caused by the ingestion of honey which may contain C. botulinum spores. Children under one year of age, unlike adults, are not able to digest the spores, which can germinate in the child's intestine where they release the toxin. It then causes constipation, followed by a lack of appetite, lethargy weakness, muscle paralysis, and possible death, though fatalities are not as common as in conventional adult botulism. Typically, the affected infant is unable to cry or suckle normally and has difficulty keeping its head up. The latter symptom has led to this kind of poisoning being designated the "limp baby disease". Because of the risks, honey should never be fed to infants.

Bacillus cereus

The FDA believes that there has recently been an increase in foodborne illnesses caused by Bacillus cereus, a facultative bacterium that lives in both vegetative and spore states in dried foods. A wide variety of foods are susceptible to B. cereus contamination, but starchy ones such as cooked rice, macaroni, and potato left at room temperature are particularly at risk. Also vulnerable are food mixtures such as casseroles, soups, pastries, salads, sauces, and puddings. Intoxication can assume one of two types: diarrheal or emetic (vomiting). The diarrheal type occurs within 6 to 15 hours of ingesting the contaminated food, while the emetic type comes on within 30 minutes to 6 hours. Both types last less than 24 hours.