Electron microscopy of bactericidal effects produced by the alternative complement pathway of channel catfish


The activation of the alternative complement pathway (ACP) was investigated by incubating serum of channel catfish Ictalurus punctatus with three gram-negative bacteria. Bactericidal activity and ultrastructural damage were not apparent when cells were incubated with serum that had been treated to eliminate complement activity. Proteins of the ACP were responsible for damaging susceptible Escherichia coli and Pseudomonas fluorescens, whereas there was no effect on Aeromonas salmonicida, which was apparently protected by an A-layer. Scanning electron micrographs revealed damaged cells, and transmission electron micrographs showed circular lesions oriented perpendicularly to the cell membrane. These lesions resemble those resulting from ACP activation in sera from frogs, sharks, trout, lizards and mammals. The existence of membrane attack complexes (MACs) in channel catfish, which are similar to MACs seen in other animals, emphasizes the importance of the ACP in host defense against bacterial infections. © by the American Fisheries Society 1991.

Publication Title

Journal of Aquatic Animal Health