A novel assay to detect macrophage bactericidal activity in fish: factors influencing the killing of Aeromonas salmonicida

A novel assay to detect macrophage bactericidal activity is reported. It utilizes the reduction of a tetrazoiium dye, MTT, to colorimetrically detect the number of surviving bacteria after incubation with the macrophages. This assay has been optimized for the killing of Aeromonas salmonicida and its advantages over conventional colony counting are discussed. Using this assay, the authors have shown that normal macrophages are able to kill an A‐layer lacking strain of A. salmonicida (004) but not an A‐layer possessing strain (048). In contrast, macrophages activated in vivo were shown to be capable of killing both strains effectively.