动物模型,大肠杆菌 z-bo 2020-08-12 543

　　The typical strain of Enterohemorrhagic E.coli (EHEC) is EHEC O157:H7. Infection with this bacteria can cause diarrhea, hemorrhagic colitis (HC), and hemolytic uremia. Syndrome (haemolytic uraemic syndrome, HuS) and thrombotic thrombocytopenic purpura (TTP) and other serious complications. Enterohemorrhagic Escherichia coli EHEC O157 was first isolated in the 1970s and was subsequently identified as a serious pathogen. In recent years, outbreaks of EHEC O157:H7 have occurred frequently all over the world and have aroused widespread concern. Because O157 bacteria can stay in the intestines of cattle, sheep, pigs, chickens and other livestock and poultry for a long time, it is easy to contaminate the meat, milk and egg products, water sources and crops of livestock and poultry, causing human O157 food-borne or water-borne infections. At present, the established EHEC animal models include mice, suckling rabbits, monkeys, suckling pigs, and chickens, but most experimental animals are not susceptible to EHEC O157: H7, so the EHEC O157: H7 models prepared are not ideal.

　　1 Mouse enterohemorrhagic Escherichia coli model

　　(1) Reproduction method BALB/c mice aged 5 to 7 weeks were given 5g/L streptomycin solution for 3 days, and then all water was cut off and fasted for 1 day, then 0.3ml of viable bacteria was orally fed 10 times with a concentration of about 1.5×10 Recipe CFU/ml of bacterial solution, challenge the bacteria for 2 consecutive times, with an interval of 6 hours, after gavage challenge, give 0.5g/L streptomycin solution for drinking. Some mice have loose stools 2 to 3 days after being fed, but no obvious symptoms of diarrhea. Most mice died within 2 to 5 days of infection. The positive rate of intestinal bacteria culture in dead and non-dead mice was 100%, and the excretion time of non-dead mice could reach more than 22 days.

　　(2) Characteristics of the model This model added streptomycin to the drinking water before the mice were inoculated with bacteria to suppress the normal flora in the intestines. The main pathological changes and some clinical features of human infection O157 were replicated in the mice. symptom. This model can be used to study the pathogenic mechanism of enterohemorrhagic Escherichia coli O157:H7 and vaccine evaluation.

　　(3) Comparative medicine. Enterohemorrhagic Escherichia coli produces Shiga-like toxin (Stx). Stx is a cytotoxin. After human infection O157:H7, Stx causes intestinal mucosal congestion, necrosis, edema and intestinal mucosa in the cecum, appendix and ascending colon. Bleeding can lead to diarrhea, hemorrhagic colitis (HC), hemolytic uremic syndrome (HuS) and thrombotic thrombocytopenic purpura (TTP) and other serious complications, and even death. Since most animals are not susceptible to EHEC O157: H7, none of the replicated models can show all the symptoms of human infection with the disease. Mice are currently the most widely used model. Although mice treated with antibiotics were fed with O157:H7 and caused animal death, the typical pathological changes included in HuS such as glomerular endothelial cell edema, platelet and fibrin deposition can also be found in small rats. It replicates in mice, but mice rarely show diarrhea. Intestinal hemorrhage and lamina propria lesions caused by O157:H7 are milder in mice, and the lesions in the lungs of infected mice are the most obvious, which may be similar to mice. There are more Stx receptors in the lungs.

　　2 Suckling rabbit enterohemorrhagic E. coli model

　　(1) Copy method About 3 days old SPF Japanese big-eared rabbits are fed 2×1000 CFU/ml O157 Escherichia coli culture medium 0.5ml through the animal mouth with a hose. Bacteria can cause diarrhea in suckling rabbits within 3 days. 77.3% of suckling rabbits have severe diarrhea on the 7th day, but no bloody diarrhea. The bacterial culture of the gastrointestinal mixture can reach 10000000～1000000000CFU/ml after 7 days of infection.

　　(2) Model characteristics The main advantage of the suckling rabbit model is that suckling rabbits are more sensitive to O157 infection and Stx, and are prone to cause diarrhea. It only needs less O157: H7 E. coli (1×1000CFU/ml) to be successfully infected without antibiotics. It destroys the normal flora of the intestine, similar to human natural infection, and can be used for model research of etiology and pathogenic mechanism.

　　(3) Comparative Medicine O157: H7 E. coli can cause severe diarrhea in suckling rabbits, but it has not replicated hemorrhagic diarrhea. Microscopic histopathological observations showed that the characteristics of vacuolar degeneration and necrosis of small intestinal epithelial cells, cecal epithelial shedding, colonic epithelial cell shedding and necrosis in suckling rabbits are similar to those of human infection with O157:H7 E. coli. In addition, it has been reported that in the outbreak of hemorrhagic diarrhea and sudden death in a group of Dutch rabbits (Duteh belted rabbits), the pathological manifestations of infected rabbits are very similar to those of humans after EHEC infection: the infected rabbits appear corrosive and Necrotizing enteroconjunctivitis, diffuse glomerulonephritis, renal tubular necrosis, and fibrinous thrombi in small blood vessels and capillaries suggest that rabbits can be used as an ideal animal model for studying human infection with enterohemorrhagic E. coli. In addition to mouse and suckling rabbit EHEC models, some researchers have infected monkeys with the O157:H7(84-01) strain. As a result, the monkeys may have watery diarrhea and may cause death. Pathological examination revealed that a large amount of O157 colonized the surface of epithelial cells in the colon. Most experimental monkeys had vacuolization of intestinal mucosal epithelial cells. The kidney, lung, spleen and liver also had obvious pathological changes. The monkey O157 infection model can also successfully replicate diarrhea, cecum and colon damage.