What Is a Shigella Infection?

Shigella Castellani is a class of Gram-negative short bacillus. It is the most common pathogen of bacterial dysentery in humans. It is mainly prevalent in developing countries. It is commonly known as dysentery bacillus. It grows for 24 hours and forms a smooth translucent colony with a diameter of 2mm. No spores, no capsules, no flagella, most pili. It is an intestinal pathogen of humans and primates, causing bacterial dysentery.

Shigella is dysentery bacillus. Shigella dysentery is a pathogen that causes typical bacterial dysentery. It can be caused by very few individuals in sensitive populations. Although this bacterium can be transmitted by food, they Unlike the other three Shigella species, it is not considered a pathogen causing food poisoning. Shigella has a weak viability outside the human body, can survive for 20 days in water at 10-37 , can survive for 1-2 weeks in milk, fruits, and vegetables, and can survive for 10 days in stool (15-25 ), under light 30mn can be killed, and it will die after heating at 58-60 for 10-30min. Shigella is cold-resistant and can survive for three months in ice cubes. Among Shigella, the viability of Shigella in Song and Shigella flexneri is relatively strong in vitro, and Shigella food poisoning is mainly caused by these two Shigella ^[1]

Biochemical reaction: Decompose glucose, produce acid but not gas. The VP test is negative, does not decompose urea, does not form hydrogen sulfide, and cannot use citrate as a carbon source. Shigella sonnei can slowly ferment lactose (3 to 4 days at 37 ° C).

With K and O antigens without H antigens. K antigen is a bacterial surface antigen of some strains newly isolated from patients. It is not heat-resistant and is destroyed by heating at 100 ° C for 1 hour. K antigen is not meaningful in serological typing, but it can prevent O antigen from corresponding antisera.

The bacteria's resistance to physical and chemical factors is weaker than other enterobacteria. Sensitive to acids, the resistance in the external environment can be strongest with S. sonnei, followed by F. flandii, and Shigella the weakest. Usually 56 60 will be killed after 10 minutes. Survived in water at 37 ° C for 20 days, and survived in ice cubes for 96 days. The intestine of the fly can survive for 9 to 10 days, is sensitive to chemical disinfectants, and died of 1% carbolic acid for 15 to 30 minutes.

(1) SR type mutation: D. dysenteriae of Songnei is easily R type. When the colony mutates, it is often accompanied by changes in biochemical reactions, antigen structure and pathogenicity.

(2) Variation in drug resistance: Due to the widespread use of antibiotics, the number of resistant strains of Shigella continues to increase, bringing much difficulty to control.

(3) Malnutrition variant: Streptomycin-dependent Shigella strain (Sd. Strain), pioneered by Yugoslav Mel (1963), can prevent Shigella dysentery as an oral vaccine.

The size is 0.5 0.7 × 2 3m, no spores, no capsules, no flagella. Most have pili. Gram-negative bacilli.

Straight bacilli

Dangers of Shigella to humans

Humans and primates are suitable hosts for Shigella, and malnourished young children, the elderly, and immunodeficiency patients are more susceptible. It is reported that there are about 14,000 cases of Shigella each year, but the estimated number of cases is 300,000. According to FDA statistics, there were a total of 8051 cases of foodborne diseases in five states including California in 1997, of which 1263 cases were caused by Shigella. Bacterial dysentery caused by Shigella was mainly transmitted through the digestive tract. Depending on the health and age of the host, only a small number of germs (at least 10 cells) are required to enter the disease. The pathogenic effects of Shigella are mainly toxins from invasive bacteria. Individual strains can produce exotoxin. After Shigella enters the large intestine, due to the action of pilus, it adheres to the epithelial cells of the large intestine mucosa, then enters the epithelial cells and multiplies inward, and spreads to adjacent cells and the subepithelial layer. Due to the action of toxins, epithelial cells die, submucosa becomes inflamed, and capillaries form thrombosis, which cause necrosis, shedding, and ulcer formation. All strains in the genus Shigella have strong endotoxins that act on the intestinal wall and increase permeability, thereby promoting the absorption of toxins, and then acting on the central nervous system and cardiovascular system, causing a series of clinical raspberry blood Symptoms such as fever, psychiatric disorders, and even toxic shock. The toxin destroys the mucous membrane to form inflammation and ulcers, which are typical of dysentery, pus and blood. The drug dysentery acts on the intestinal wall autonomic nerves, causing intestinal dysfunction, ataxia and spasm of intestinal peristalsis, especially the rectal sphincter is most obvious, so symptoms such as abdominal pain and anxiety may occur. Shigella type 1 and some type 2 (Shigella shigella) strains can produce a potent exotoxin, which is a protein and is not heat-resistant and can be destroyed at 75 ~ 80 ° C for 1 hour. Its role is to increase the permeability of the intestinal mucosa and cause damage to vascular endothelial cells. Exotoxin can be detoxified into toxoids by treatment with formaldehyde or ultraviolet light, which can stimulate the body to produce corresponding antitoxins. Diarrhea caused by Shigella with exotoxin is generally considered to be more serious ^[2] .

Shigella preventive measures

Shigellosis is often an outbreak of a foodborne disease or an outbreak of a waterborne disease. Foods related to Shigella include salads (potatoes, tuna, shrimp, macaroni, chicken), raw vegetables, milk and dairy products, poultry fruits, bread products, hamburgers and finned fish. Shigella can spread rapidly in crowded and unhygienic conditions and is often found in places with large numbers of people, such as restaurants and canteens. The most important cause of foodborne Shigella is the contamination of food by people working in the food processing industry with bacteria or carriers, poor personal hygiene of food contact personnel, improper storage of contaminated food, etc. to prevent and control Shiga The best measure for the spread of mycosis is good personal hygiene and health education. Sanitary treatment of water and sewage can also prevent the outbreak of water-borne Shigella. Suspicious foods include foods that have been processed by hand or lightly heated before consumption, animal foods, or foods directly consumed by consumers, and the acidity range is between pH 5.5 and 6.5. In general, when foods contain coliforms, E. coli, and Salmonella, the possibility of Shigella is extremely high. In addition to the "three-early" measures (early diagnosis, early isolation, and early treatment) for acute bacillary dysentery, chronic bacillary dysentery, and various carriers, in order to eliminate the source of infection, a comprehensive approach based on cutting off the route of transmission should be adopted. Sexual measures. Carry out patriotic worker-student movements, do a good job in the management of the food processing and catering service industry, and carry out regular inspections of carriers of food processing personnel.