Interaction between Aeromonas salmonicida and peritoneal macrophages of brook trout (Salvelinus fontinalis)

The phagocytic and bactericidal properties of peritoneal macrophages obtained from brook trout (Salvelinus fontinalis), injected with either glycogen or a modified Freund's complete adjuvant (MFCA), were evaluated against an avirulent and a virulent strain of Aeromonas salmonicida. Avirulent bacteria were effectively phagocytized and killed by macrophages obtained from fish injected with both irritants. With glycogen-elicited macrophages, no enhancement of killing was observed following opsonization of avirulent bacteria with specific antibodies. A killing index (K.I.) of 38 was obtained, compared to a K.I. of 39 for unopsonized bacteria. When avirulent bacteria were opsonized with complement, the K.I. was increased to 67. Virulent bacteria were less susceptible to the phagocytic and the bactericidal activities of glycogen-elicited macrophages, even after opsonization with antibodies and/or complement, K.I. of 9 to 15. In contrast, MFCA-elicited macrophages showed increased phagocytic and bactericidal activities against both strains. The K.I. of unopsonized virulent bacteria was increased to 47 and 46 compared to K.I. of 4 and 7 obtained with glycogen-elicited macrophages.