| Enterohemorrhagic E.coli(EHEC)belongs to Shiga toxin-producing E.coli family and is a food-borne zoonotic pathogen that is widely distributed in nature and causes harm to humans and animals.The major pathogenic strain of enterohemorrhagic E.coli is the O157:H7 serotype,which can cause a series of complications such as mild infection,watery diarrhea,hemorrhagic enteritis,and hemolytic uremic syndrome(HUS).In severe cases can cause the death of the body.The uses of rabbits mainly include:use as experimental animals,as special animal breeding,as a food source,and as a companion pet.During the rabbit’s growth,it is often threatened by EHEC infection,which usually results in diarrhea or even rapid death.In this study,two bacterial strains,TS and MY,were isolated from the intestine of naturally infected rabbits with naturally occurring acute diarrhea.After selective culture,the suspected colonies were stained by microscopy and molecular biology methods determined that both belonged to E.coli.The classical virulence genes of EHEC were further amplified by gene cloning and RT-PCR.The main virulence factors of EHEC in infection can promote its ability to adhere to intestinal epithelial cells,causing intestinal damage and Shiga toxin production.In order to elucidate the pathogenic mechanism and host innate immune response of EHEC in rabbits,the above-mentioned isolated TS and MY strains were used in this study.Systemically describes the bacterial content,clinical signs,histopathological changes,and innate immune responses in various tissues infected with EHEC rabbits.The results showed that rabbits infected with the MY and TS strains of bacteria exhibited typical clinical symptoms.The infected rabbits showed mental depression,loss of appetite,and diarrhea.They also showed typical pathological changes such as fibrinous pericarditis,endocardial hemorrhage,and liver and spleen were swollen and had white cellulose exudates.Although in the stable period of bacterial growth,the maximum number of TS strains was6.46×10~9CFU/mL,which was higher than that of MY strains 2.29×10~9CFU/mL.However,the incidence and mortality of diarrhea in rabbits infected with MY strains were higher than those in infected TS strains.And in the typical symptoms observed in two groups of bacterially infected rabbits,the histopathologic changes in the heart,liver,and spleen of rabbits infected with the MY strain were more severe than those infected with the TS strain.To study the innate immune mechanism of rabbits infected with EHEC and to investigate the inflammation and anti-bacterial responses of the body,the present study further examined the expression of major inflammatory cytokines and defensins in the liver and spleen of rabbits.In both liver and spleen,both MY and TS strains can induce up-regulation of pro-inflammatory cytokines IL-1β,IL-6,IL-8,IFN-γ,and TNF-α;and after 3 dpi,the expression levels ofα-defensin andβ-defensins were significantly upregulated.The MY-strain induced expression ofα-defensin andβ-defensins in the spleen was higher than that induced by the TS strain.It was concluded that MY-strain induced expression ofα-defensin andβ-defensins in the spleen was higher than that of the TS strain.However,the TS strain induced higher expression ofα-defensin andβ-defensins in the liver than the MY strain.The most probable cause is that the proliferation processes of MY and TS strains in liver and spleen are different,thereby inducing different immune responses.In this study,the clinical symptoms,histopathological changes,bacterial content major inflammatory cytokines and defensins was measured in rabbit after infected with EHEC TS strain and MY strain.The role of lethality and innate immunity in the infection process offers new perspectives.In conclusion,the results of this study provide new perspectives for the occurrence and development of diseases mediated by EHEC TS strain and MY strain,and provide some useful reference information for diagnosing the infection caused by this strain in clinical practice. |
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