Studies on diseased freshwater prawn Macrobrachium rosenbergii infected with Vibrio vulnificus

The present study was aimed at isolation and characterization of the pathogenic bacterium from diseased freshwater prawn. The effect of the bacterial pathogen on hepatopancreas, gills and exoskeleton was also investigated. Diseased freshwater prawn, Macrobrachium rosenbergii were collected from commercial hatchery in Behera Governorate, Egypt. The diseased prawn showed dark brown focal lesions and necrosis of appendage tips. The causative bacterial pathogen was isolated from haemolymph and hepatopancreas of the diseased prawn. Based on the morphological, biochemical and physiological characteristics, in addition EPI 20E test, the isolated pathogen was characterized as Vibrio vulnificus. Histopathology, hepatopancreas showed haemocytic infiltration in the interstitial sinuses, thickening and ruptures of the basal lamina and necrosis of its tubules. Similarly, the accumulation of haemocytes in the haemocoelic space, swelling, fusion of lamellae and abnormal gill tips. Also, the cuticular layers of the exoskeleton of diseased prawn had a rough or wrinkled surface and were disrupted and separated from the epidermis. The pathogen, V. vulnificus showed different degrees of sensitivity to different antimicrobial agents. It was highly sensitive to each of the antibiotics rifadin, virbamycin, oflaxcin, garamycin, flummox and trimethoprim/sulfamethoxzole) and resistant to nalidixic acid, unasyn, velosef, claforan, negram and amoxicillin. The minimal inhibitory concentration of trimethoprin/sulfamethoxzole for the studied pathogen, V. vulnificus was 0.31/5.93 microg.