Tissue Tropism Of Vibrio Mimicus In Infected Yellow Catfish, Pelteobagrus Fulvidraco And Its Hispathological Lesions

In this study, yellow catfish (Pelteobagrusfulvidraco) (weight 75.5±5.0g)were experimentally infected by immersion challenge with V.mimieus(1.0×106 CFU·mL-1). Challenged fish were sampled at 0 h,4 h,8 h,16 h,24 h,36 h,48 h,60 h and 72 h post infection to detect the histopathological changes and distribution of bacteria, respectively. The diseased fish display lethargy, loss of appetite, shaped ulcers with clear boundaries in fish skin and swollen of anus. Internally, the liver was pale and with petechiae, kidney and spleen were congested. Hemorrhaging of gill, accumulation of reddish ascetic fluid, bleeding of peritoneal were also found internally. Pathologic results showed that skin, muscle, gills and intestines were the first to produced pathologic changes, as while the skin and muscle were the most serious damaged. Degeneration of the epidermis,mild hemorrhages of dermis and gill edema of the gill epithelium and intestinal mucous membrane were observed at 16 h post infection.Then, severe hemorrhages in dermis. widened space and infiltrated with inflammatory cells of muscle, strong lysis of muscle fibers, expend and hemorrhages of gill filament, edema and exfoliation of epithelial cells in gill secondary lamellae, edema of the intestinal mucous membrane and separation with the lamina propria were observe from 24 h to 48 h; At the period 48 to 72 h, skin and muscle fibers formed ulcer lesions and gills showed hemorrhages and focal necrosis. Besides, the organs of liver, spleen, kidney, heart showed different degrees of pathological changes after 36 h post infection, including congestion, hemorrhage, degeneration and focal necrosis.At the period 48 to 72 h. dermis and muscle fibers formed ulcer lesions, as while a mass of bacterial was found in muscle, gills showed hemorrhages and focal necrosis.. At 36 h. kidney showed congestion, the glomeruli was extensive. Besides, the organs of liver, spleen, kidney, heart showed different degrees of pathological changes after 36 h post infection, including congestion, hemorrhage, degeneration and focal necrosis.The real-time PCR results showed that V.mimicusis be detected in gills, intestines and muscle initially at 4 h post infection and the quantitly of bacteria were 1.3×102 CFU·mg-1 in intestines.2.6×102 CFU·mg-1 in gills and 4.7×102 CFU·mg-1in muscle, respectivrly.The quantitly of bacterial in intestines was decreased for the rest of the time, but the number in gill and muscle were increased,and then reached a peak at 72 h, being 4.7×103 CFU·mg-1 and 4.5×107 CFU·mg-1 respectively. After 24 h,V.mimicus was detected in kidney. After 36 h?V.mimicusis be detected in liver, spleen and heart, the range of quantitly were from 1.9×101 CFU·mg-1 to 4.7×102 CFU·mg-1. There was no V.mimicus be detected in brain. The real-time PCR result is consisted with the histopathological changes. Both of them show that gill, intestine, muscle are those organs which V.mimicus adhering first and most of the internal organs can also be invaded besides muscle is the primary target organ to reproducing in. In addition, the result of immunohistochemistry show that loss connective tissus of skin and muscle is the main tissue whice Vibrio mimicus adhere to.