Microbiology and Immunology

Salmonella food poisoning WORLD OF MICROBIOLOGY AND IMMUNOLOGY

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Products containing animal tissues may also be contaminated

with Salmonella.

While anyone may contract Salmonellafood poisoning

from contaminated foods, the disease proves most threatening

in infants, the elderly, and individuals with weakened immune

systems. People who have had part or all of their stomach or

spleen removed, as well as individuals with sickle cell anemia,

cirrhosis of the liver, leukemia, lymphoma, malaria, louse-

borne relapsing fever, or acquired immunodeficiency syn-

drome (AIDS) are particularly susceptible to Salmonellafood

poisoning. In the United States, about 15% of all cases of food

poisoning are caused by Salmonella.

Salmonella food poisoning occurs most commonly

when people eat undercooked chicken or eggs, sauces, salad

dressings, or desserts containing raw eggs. The bacteria can

also be spread if raw chicken, for example, contaminates a cut-

ting board or a cook’s hands, and is then spread to some other

uncooked food. Cases of Salmonellainfections in children

have been traced to the children handling a pet (such as a tur-

tle or an iguana) and then eating without first washing their

hands. An individual who has had Salmonellafood poisoning

will continue to pass the bacteria into their feces for several

weeks after the initial illness. Poor handwashing can allow

others to become infected.

Symptoms of Salmonellafood poisoning generally

occur about 12–72 hours after ingestion of the bacteria. Half

of all patients experience fever; other symptoms include nau-

sea, vomiting, diarrhea, and abdominal cramping and pain.

The stools are usually liquid, but rarely contain mucus or

blood. Diarrhea usually lasts about four days. The entire ill-

ness usually resolves itself within about a week.

While serious complications of Salmonellafood poi-

soning are rare, individuals with other medical illnesses are at

higher risk. Complications occur when the Salmonellabacte-

ria make their way into the bloodstream. Once in the blood-

stream, the bacteria can invade any organ system, causing

disease. Infections which can be caused by Salmonella

include: bone infections (osteomyelitis), infections of the sac

containing the heart (pericarditis), infections of the tissues

which cover the brain and spinal cord (meningitis), and liver

and lung infections.

Salmonellafood poisoning is diagnosed by examining a

stool sample. Under appropriate laboratory conditions, the

bacteria in the stool can be encouraged to grow, and then

processed and viewed under a microscopefor identification.

Simple cases of Salmonellafood poisoning are usually

treated by encouraging good fluid intake, to avoid dehydra-

tion. Although the illness is caused by a bacteria, studies have

shown that using antibioticsmay not shorten the course of the

illness. Instead, antibiotics may have the adverse effect of

lengthening the amount of time the bacteria appear in the

feces, thus potentially increasing others’ risk of exposure to

Salmonella.Additionally, some strains of Salmonellaare

developing resistance to several antibiotics.

Efforts to prevent Salmonellafood poisoning have been

greatly improved now that it is understood that eggs can be

contaminated during their development inside the hen. Flocks

are carefully tested, and eggs from infected chickens can be

pasteurized to kill the bacteria. Efforts have been made to

carefully educate the public about safe handling and cooking

practices for both poultry and eggs. People who own pets that

can carry Salmonellaare also being more educated about more

careful handwashing practices. It is unlikely that a human

immunizationwill be developed, because there are so many

different types of Salmonellaenteritidis. However, researchers

in 1997 produced an oral vaccinefor poultry from genetically

altered live Salmonellabacteria, currently undergoing testing,

that may show the prevention of Salmonellabacteria from

infecting meat or eggs. In 2001, two teams of researchers in

England sequenced the genomes of both Salmonella

Typhimurium (a common cause of food poisoning) and

Salmonella Typhithe cause of typhoid fever). Data gathered

from the project will improve diagnosis of Salmonellainfec-

tions, and may eventually lead to a method of blocking its

transmission in humans.

See alsoAntibiotic resistance, tests for; Bacteria and bacterial

infection; Bacterial adaptation; Food safety

SSalmonella food poisoningALMONELLA FOOD POISONING

Salmonellafood poisoning, consistent with all food poisoning,

results from the growth of the bacterium in food. This is in

contrast to food intoxication, were illness results from the

presence of toxin in the food. While food intoxication does not

require the growth of the contaminating bacteriato reasonably

high numbers, food poisoning does.

Salmonellais a Gram negative, rod-shaped bacterium.

The gastrointestinal tracts of man and animals are common

sources of the bacterium. Often the bacterium is spread to food

by handling the food with improperly washed hands. Thus,

proper hygieneis one of the keys to preventing Salmonella

food poisoning.

The food poisoning caused by Salmonellais one of

about ten bacterial causes of food poisoning. Other involved

bacteria are Staphylococcus aureus, Clostridium perfringens,

Vibrio parahaemolyticus, and certain types of Escherichia

coli. Between 24 and 81 million cases of food borne diarrhea

due to Salmonellaand other bacteria occur in the United States

each year. The economic cost of the illnesses is between 5 and

17 billion dollars.

Poultry, eggs, red meat, diary products, processed

meats, cream-based desserts, and salad-type sandwich filling

(such as tuna salad or chicken salad) are prime targets for col-

onization by species of Salmonella. The high protein content

of the foodstuffs seems to be one of the reasons for their sus-

ceptibility. Contaminationis especially facilitated if improp-

erly cooked or raw food is held at an improper storage

temperature, for example at room temperature. Proper cooking

and storage temperatures will prevent contamination, as

Salmonellais destroyed at cooking temperatures above 150° F

(65.5 °C) and will not grow at refrigeration temperatures (less

than 40°F, or 4.4°C). Also, contamination can result if the food

is brought into contact with contaminated surfaces or utensils.

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