Definition of Shigella

Shigella is a class of Gram-negative bacilli, human bacillary dysentery is the most common pathogens, commonly known as dysentery bacilli, cold, can grow in the general medium, the formation of medium-sized, translucent smooth type Colony. A colorless colony was formed on the selective medium of Enterobacteriaceae.

Biochemical reactions of Shigella

Decomposition of glucose, acid-producing gas. VP test negative, not the decomposition of urea, does not form hydrogen sulfide, can not use citrate as a carbon source. Shigella sonnei can slowly ferment lactose (37℃ 3 to 4 days).

Pathogenic immunity

Pathogenic substances:

1. Invasion force: Shigella fimbriae can adhere to the terminal ileum and colonic mucosal epithelial cell surface, and then penetrate into the epithelial cells under the action of the invasion protein, usually in the lamina propria to form a foci of infection. In addition, where K antigen with Shigella, the general pathogenicity is strong.

2. Endotoxin: Shigella dysenteriae have a strong endotoxin. Endotoxin on the intestinal wall, so that increased permeability, and promote endotoxin absorption, causing fever, consciousness disorders, and even toxic shock. Endotoxin can destroy the mucosa, the formation of inflammation, ulceration, there will be a typical pus mucus mucus. Endotoxin also acts on the intestinal wall of the autonomic nervous system, to intestinal disorders, bowel disorders and hydrogen spasm, especially the most obvious sphincter spasm, abdominal pain, tenesmus (frequent it intended) and other symptoms.

3. Exotoxin: Shigella A group Ⅰ and part of the type 2 strains can also produce exotoxin, said Shiga toxin. For the protein, not heat, 75 ~ 80℃ 1 hour is destroyed. The toxin has three biological activities: ① neurotoxicity, the injection of toxins in rabbits or mice, acting on the central nervous system, causing limb paralysis, death; ② cytotoxicity of human liver cells, monkey kidney cells and HeLa cells are Toxicity; ③ enterotoxic, with similar E. coli, Vibrio cholerae enterotoxin activity, can explain the disease early watery diarrhea.

Caused by disease:

Bacterial dysentery is the most common intestinal infectious diseases, summer and autumn patients the most. The main source of infection for patients and carriers, by contaminated Shigella bacteria food, water and other oral infection. Human susceptibility to Shigella, 10 to 200 bacteria can make 10 to 50% of the volunteers pathogenesis. In general, Shigella dysentery caused by the disease heavier; Senebacterium caused by the symptoms of mild; between the two bacteria, but the long row of bacteria, easy to chronic.

1. Acute bacillary dysentery: divided into a typical bacillary dysentery, atypical bacillary dysentery and dysentery type three. Toxic dysentery more common in children, various types of dysentery bacilli can be caused. Acute onset, often in abdominal pain, diarrhea does not appear, showing severe systemic symptoms of poisoning.

2. Chronic bacillary dysentery: acute bacillary dysentery treatment is not complete, or low body resistance, malnutrition, or associated with other chronic diseases, easy to chronic. Course of more than two months or more, delayed healing or when the hair.

Some patients may become carriers, carriers can not engage in catering, cooking and conservation work.

Principles of prevention and control:

Specific prevention of oral live attenuated live vaccine mainly, the trial were Sd strains, Shenshifan 2a variants and so on. These live vaccines, although a certain preventive effect, but weak immunity, maintenance time is short, and taking large, no cross-protection between the cross-immunity. So large-scale application is also subject to certain restrictions.

Treatment can be sulfa drugs, ampicillin, chloramphenicol, berberine and so on. Chinese medicine Coptis, Phellodendron, Pulsatilla, Purslane, etc. are effective.

Immunity:

Immunity is not strong after the disease, can not prevent re-infection. But the same epidemic period less re-infection, that is, with type-specific immunity. Shigella dysenteriae type, no cross-immunity between the various types. The body's immunity to bacillary dysentery depends mainly on the intestinal immune, that is, enhanced intestinal mucosal phagocytosis and SlgA role. SlgA can prevent the adhesion of dysentery bacilli to the surface of intestinal epithelial cells, about three days after the disease appears, but the maintenance time is short, because Shigella does not invade the blood, so serotype antibodies (lgM, lgG) can not play a role.

Way for spreading:

Mainly fecal - oral route of transmission. Shigella dysentery with the patients or carriers of the feces, through the contaminated food, water, hand and other oral transmission.

Diagnosis of Shigella

Specimen: In the feces before taking the pus and blood or mucus part of the specimen can not be mixed with urine. If not timely submission, specimens should be stored in 30% glycerol buffer saline or enrichment culture medium. Toxic bacillary dysentery desirable anal swab examination.

Isolation, Culture and Identification

Inoculation of intestinal bacteria selective medium, 37℃ incubation 18 to 24 hours, pick a colorless translucent suspicious colonies, for biochemical reactions and serological agglutination test to determine the flora and bacteria. In case of atypical strains, the system must be biochemical reactions to determine the genus; if necessary, with the amount of bacteria inoculated on the guinea pig conjunctiva, observed 24 hours, if inflammation, compared with toxic strains.

Rapid diagnostic method

1. Fungal ball method: suitable for the examination of acute bacillary dysentery of stool specimens. The samples were inoculated in a serum-free liquid medium containing fluorescein-labeled Shiga, and cultured at 37°C for 4 to 8 hours. If there is a corresponding type of dysentery bacilli in the specimen, after breeding and fluorescein antibody agglutination into small bacteria ball, low magnification or high power fluorescence microscope easy to detect. The method is simple, rapid and specific.

2. Synergistic agglutination test: Shigella lgG antibody and A protein-rich Staphylococcus aureus as a reagent, the determination of fecal filtrate in patients with Shigella soluble antigens.