Identification And Pathogenetic Analysis Of Aeromonas Caviae From Fox

Aeromonas caviae found widely in nature belongs to conditional pathogenic bacteria that can infect human and many kinds of aquatic animals.In June,2015,foxes were infected incidentally by pathogenic bacteria in a farm in Anshan,Liaoning Province.The hind limbs of dead foxes were found to get ulcers.The cause of death was investigated in lab.1.A dominant strain was isolated from the center of lesion and named M12.Comprehensive phenotype identification,16S rRNA and GyrB gene identification,physiological characteristics analysis,virulence gene detection,mouse toxicity test,and drug sensitivity test were carried out respectively to analyze this strain.The results showed that M12 is a rod-shaped gram-negative Aeromonas caviae with the optimum growth temperature at 30℃,and pH between 7 and 8.BLAST indicated that 16S rRNA and GyrB genes of M12 were found to be homologous with that of Aeromonas caviae in GenBank.The sequencing result of 16SrRNA was submitted to the GenBank and the accession number（KX170836）was obtained.M12 contained cytotoxic enterotoxin（act）and heat-Labie cytotonic enterotoxin（alt）.The bacteria had a high pathogenic activity with an LD₅₀ of8×10⁸ CFU/ml in mice and strong sensitivity to cephalosporins to provide evidence for the prevention.2.We explored the mechanism of M12 via in vitro tissue culture（IVOC）of ileum and intramuscular injection.Microscope and electron microscope were also used to find out the structure,infection process of M12 and changes of infected tissues.Results showed that the size expect flagellum of M12 is from 0.6 to 0.6μm×0.6 to 0.7μm（length×width）while length of flagellum is about 2 to 3 times of the length of bacteria;IVOC test observed adhesion of M12 to intestinal epithelial cells,resulting in formulation of biofilm structure and damage.Histopathologic examination found that M12 can caused damage in intestine,liver,lung,kidney and muscle tissue of rabbit this study will lay the foundation for researching the pathogenic mechanism of Aeromonas caviae.3.After extracted from M12,the major components,protein content and toxicity of extracellular product（ECP）to Vero cells were detected.Pathogenicityof ECP was also researched by intramuscular injection and intestinal loop test.The results showed that the ECP contained the protease,amylase,esterase andgelatinase with urease activity.ECP of M12 had acytotoxic effect on Vero cells and enterotoxin activities to intestinal tract.ECP was sensitive to temperature（37℃）and pH（7.0）.SDS-PAGE of ECP of M12 showed three proteins bands（36 kD,42 kD,and 68 Kd）.The muscle tissue of the rabbits was observed to dissolve in leg followed by injection of ECP;the contents of intestine increased significantly after injection of ileum.In conclusion,M12 had many virulent factors with close relationship to its pathogenicity.