Isolation And Characterization Of Streptococcus Agalactiae In Rabbit And Pathology And In Situ PCR After Experimental Infection

A pathogenic bacterium (P110323) was isolated from the liver, lung, cerebrum and heart blood of the diseased rabbit. In artificial infection studies, rabbits with P110323, proved it was the pathogen of the disease, disease signs and a mortality rate of60%were noted after postinoculation with106CFU/mL bacterium; The clinical symptoms of infected rabbits included incoordination, lateral prostration, paddling and convulsions with acute respiratory distress syndrome. Necropsy revealed degeneration and necrotic changes in many organs, especially, serious lesions occurred in the liver and kidney. Hemorrhage and swelling of the lung and spleen were considerable; The surfece of gyri was swollen and flattened with the shallow cerebullar sulci, hyperemia of meninges was obviously. The isolated bacterium was a Gram-positive cocci which possessed P-hemolytic activity on agar media with5%sterile sheep’s blood and had moistening and gray colonies in BHI. To the detection of antimicrobial susceptibility, the strains were highly sensitive ampicillin, gentamycin, norfloxacin, ofloxacin, fortum, florfenicol and resistance to penicillin, streptomycin, amoxicillin, amikacin and tobramycin. Arginine, hippuric acid and v-p test were positive; Esculin, Sorbitol and Mannitol were negative. Phylogenetic analysis show that it was hardly differentiated between S. difficilis and S. agalactiae on the basis of16S rRNA, however, the phylogenetic tree constructed by comparing gyrB sequences of the separated strain show that P110323belonged to S.agalactiae. According to the morphological, biochemical characteristics and phylogenetic analysis, the isolated strain was identified as S. agalactiae. Multiplex PCR method for the direct identification of the capsular type indicated P110323was S. agalactiae la.We used rabbits to simulation the nature disease each by intragastric administration challenge. After challenge, we recorded the pathological clinical of each group. Rabbits were euthanized at0h,6h,12h,18h,24h,48h,72h,96h.......10d and samples of cerebrum, heart, liver, spleen, kidney, lung were aseptically collected in par formaldehyde(4%) for research through pathology, cell pathology and in situ PCR. The results showed that the positive signal was detected firstly in stomach at6h after injection with hyperemia and epithelial necrosis. The positive signals appeared in spleen at12h after injection with the reduction of lymphocytes, inflammatory cell infiltration and diffusive hemorrhage and necrosis. Positve signals was detected in lung at12h and pathologic changes included hemorrhage, hyaline membranes, abscission of pulmonary epithelial cell and macrophages infiltrates. Positive signals appeared in kidney and liver at24h, and the patholoy results showed that Disseminated intravascular coagulation (DIC) and many blood vessels were congested in the renal interstitium associated with hyaline thrombus. Granular degeneration and diffuse necrosis were also seen in the liver. The signals were detected in heart and cerebellum at2d after injection. The patholoy results show necrosis and disruption of cardiac muscle fibers, and necrosis of neurons and lesion of myelin sheath were observed in cerebellum.