Staphylococcal food poisoning

Introduction to staphylococcal food poisoning Staphylococcal food poisoning is caused by eating food contaminated with enterotoxin produced by staphylococci. The clinical features are acute onset, severe vomiting, abdominal pain, diarrhea and other gastrointestinal symptoms. In severe cases, water loss and collapse can occur. Most patients disappeared after 1 to 2 days and recovered faster. basic knowledge The proportion of illness: 0.32% Susceptible people: no special people Mode of infection: non-infectious Complications: Dehydration Muscle spasm

Staphylococcal food poisoning etiology

(1) Causes of the disease

Staphylococcus aureus, spherical or elliptical, Gram-positive bacteria, 0.5-1.2 m in diameter, typically arranged in a grape-like arrangement, without flagellum, without spores, after incubation for 24 to 48 hours on solid agar medium. The surface of the colony is smooth, moist, opaque, initially white, and then golden yellow. The food poisoning is limited to the strain of Staphylococcus aureus which produces enterotoxin. The enterotoxin is a group of single-stranded peptides with a molecular weight of 27,500. ~30000, the toxin is heat stable. It can only kill Staphylococcus aureus at 100 °C for 30 minutes, but can not destroy enterotoxin, and is resistant to various digestive enzymes. However, at pH 2, it can be destroyed by pepsin. There are eight serotypes, namely A, B, C1, C2, C3, D, E and F. The same strain can produce two or more enterotoxins, but often one type of toxin, type A and type E. There is cross-immunization between type B and type C. Each type of enterotoxin can cause food poisoning, but food poisoning is most common with type A and type D enterotoxin, followed by type B and type C, enterotoxin. The poisoning dose to humans is generally considered to be 20 ~ 25 g, when staphylococci contaminate food, under the condition of insufficient oxygen, the temperature is 20-30 °C, and after 4~5h reproduction, a large amount of enterotoxin is produced. If people eat staphylococcal food contaminated with enterotoxin, Food poisoning can occur.

(two) pathogenesis

The course of the disease is short-lived, and the change of gastrointestinal function is the direct effect of enterotoxin on the gastrointestinal mucosa. It has nothing to do with staphylococcal itself. It has been shown from animal experiments that intravenous injection of very small doses of enterotoxin can cause vomiting, diarrhea and fever in animals. , low blood pressure, rapid heart rate, pulmonary edema and other syndromes, after oral enterotoxin 2h, acute gastrointestinal symptoms appear, 4 to 6h peak, the mechanism is that enterotoxin is caused by the vagus nerve and spinal cord to the vomiting center However, most believe that the main enterotoxin acts on the intestinal epithelial cells and binds to its receptor, which activates the adenylate cyclase on the intestinal epithelial cell membrane, which removes the adenosine triphosphate (ATP) from the cytoplasm. Phosphoric acid, converted to cyclic adenosine monophosphate (cAMP), increased cAMP content, promotes cytoplasmic protein phosphorylation, causing a series of enzymatic reactions, inhibiting the absorption of sodium and water by intestinal epithelial cells, and promoting intestinal and chloride secretion. , causing a large amount of fluid accumulation in the digestive tract, causing spitting and diarrhea symptoms, due to the death of the disease, severe autopsy and animal observations can be seen in the stomach and small intestine mucosa congestion, edema, Film erosion, hemorrhage, necrosis, filled with gas and liquids, in some cases still see colonic inflammation and bleeding in the intestine; liver, kidney, lungs and other internal organs congestion toxic lesions.

Staphylococcal food poisoning prevention

Strengthen diet management, isolate patients with mastitis, cooks with skin suppuration or those engaged in catering should temporarily transfer their work.

Staphylococcal food poisoning complications Complications Dehydration muscle spasm

Severe cases can cause dehydration, collapse and muscle spasm due to severe vomiting and diarrhea.

Staphylococcal food poisoning symptoms common symptoms gastrointestinal symptoms diarrhea nausea dehydration watery stool loose stools

The incubation period is 2 to 5 hours, rarely more than 6 hours. The onset is rapid, there is nausea, vomiting, middle and upper abdominal pain, followed by diarrhea, vomiting is most prominent, vomit can carry bile, mucus and bloodshot, diarrhea is watery or Lean stools, ranging from several times to dozens of times a day, severe cases can cause dehydration due to severe vomiting and diarrhea, collapse and muscle spasm, body temperature is mostly normal or slightly higher, most patients recover quickly within a few hours or within 1 to 2 hours.

Examination of staphylococcal food poisoning

1. Direct microscopic examination will detect suspicious food, vomit, feces as smear, Gram stain, under the microscope, according to the morphology, arrangement and staining characteristics of Staphylococcus, generally required to exceed 25% of other bacteria, per gram of food The bacteria should reach several hundred million, and the diagnosis can be established.

2. Bacterial culture of suspected food, vomit or feces by high-salt blood agar medium or with lithium chloride salt yolk. If no staphylococci are detected, the diagnosis cannot be denied because the bacteria are killed when the food is heated. However, enterotoxin is resistant to high temperatures and cannot be destroyed, and it can still cause disease.

3. Toxin Determination Serological Tests Serological tests are used to directly detect enterotoxin from food extracts, cultures or filtrates.

1 reverse indirect hemagglutination method: red blood cells treated with various types of enterotoxin immunoglobulin-sensitized tannic acid, and then added to the specimen containing enterotoxin, after one or two hours of blood cell agglutination positive, can be used for rapid diagnosis .

2 Immunofluorescence: The fluorescein-labeled antitoxin serum was mixed with a staphylococcal culture or a food filtrate, and the enterotoxin was examined under a fluorescence microscope.

3 Radioimmunoassay: Enterotoxin was examined by radioimmunoassay with 125I-labeled enterotoxin.

In the animal experiment, suspicious food or vomit was inoculated into the broth culture medium. After the incubation, the filtrate was injected into the abdominal cavity of the cat. The symptoms of food poisoning occurred 4 hours, suggesting that there may be enterotoxin.

Diagnosis and identification of staphylococcal food poisoning

diagnosis

According to the eating of suspicious foods, the same food has a history of onset, combined with short incubation period, short duration of gastrointestinal symptoms, no fever, rapid recovery and other characteristics can make a preliminary diagnosis, such as a large amount of drug production from the patient's vomit or feces Can be confirmed by staphylococci or food specimens that contain a large amount of staphylococci that produce enterotoxin.

Differential diagnosis

The disease needs to be differentiated from diseases such as cholera and paracholera, acute bacterial dysentery, viral gastroenteritis, and non-bacterial food poisoning.

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