Characterization of Histopathological and Ultrastructural Changes in Channel Catfish Experimentally Infected with Virulent Aeromonas hydrophila

Abstract

A highly virulent clonal population of Aeromonas hydrophila (vAh) has been the cause of recent motile Aeromonas septicemia epizootic in channel catfish (Ictalurus punctatus) farms in the Southeastern United States. The pathology of the disease caused by vAh has not been studied well yet. Thus, our aim was to determine histopathological and ultrastructural changes in channel catfish following vAh challenge. To accomplish this, catfish fingerlings were challenged with vAh (strain ML09-119) by bath. Six fish per each time point were collected at 1, 3, 5, 6, 24, and 48 h for light microscopy, and six fish were collected at 48 h for transmission electron microscopy (TEM). The first pathological lesions were detected in the spleen and stomach at 1 h post-challenge (HPC) while intestine, gills, kidney, and liver lesions were observed at 24 and 48 HPC. Histopathological examination revealed degenerative changes, necrosis, extensive edema, and inflammation in internal organs. The TEM showed severe tissue destruction with multiple bacterial cells secreting outer membrane vesicles, especially in spleen and gills and far number in the stomach. Degenerated bacterial cells were observed in the intestinal lumen and the phagosomes of phagocytic kidney cells. We identified, for the first time, degranulate eosinophilic granular cells, and dendritic cells like (DC-like) cells in the necrotic intestinal epithelium. These findings suggest that vAh rapidly proliferated and spread through the catfish organs following bath challenge.

Natural co‐infection of cultured Nile tilapiaOreochromis niloticuswithAeromonas hydrophilaandGyrodactylus cichlidarumexperiencing high mortality during summer

“…These pigmented cells may appear isolated or in the form of a cluster where it indicates the positive presence of neutral carbohydrate and melanin (Agius & Roberts, ). Our results were much like the findings found in other fish species in previous investigations (Abdelhamed, Ibrahim, Baumgartner, Lawrence, & Karsi, ; Brenden & Huizinga, ; Cipriano, Bullock, & Pyle, ; Kumar et al, ; Stratev, Stoev, Vashin, & Daskalov, ).…”

Fish pathogen binding to mucins from Atlantic salmon and Arctic char differs in avidity and specificity and is modulated by fluid velocity

“…hydrophila interaction. Another study in channel catfish, focusing on histological changes, showed lesions to appear first in the stomach and spleen, then in the intestine, and only after that on the gills [56]. Thus, in channel catfish, the adherence of A .…”

“…Thus, in channel catfish, the adherence of A . hydrophila to mucins shows an inverse relationship with the pathological signs [55, 56]. This inverse relationship could be explained by the mucins potentially acting as releasable decoys, i.e.…”

Recombinant ATPase of Virulent Aeromonas hydrophila Protects Channel Catfish Against Motile Aeromonas Septicemia

“…At 3 weeks post-immunization, catfish were experimentally infected by bath immersion with 2.8 × 10 10 CFU/ml of A. hydrophila ML09-119 for 6 h at 30°C (17). Bacterial infection dose was chosen based on previous experimental infection doses (8, 18). Bacteria numbers (CFU/ml) in the overnight cultures were determined by plating serial 10-fold dilutions on agar plates followed by viable colony counts.…”