Microbial Succession in Gliding Bacterium Infection in Red Sea Bream

Abstract

It is reported that the gliding bacterium is isolated at the early stage and Vibrio sp. is isolated at the later stage in the gliding bacterium infection in red sea bream Pagrus major. But it is not clealy understood which bacterium is the major cause of the infection or how the succession occurs.
In this study, two strains of Flexibacter marinus R-3 and Vibrio sp. Kg-l were inoculated in red sea bream under various conditions to clarify the problem mentioned above. Fish were inoculated wity F. marinus by smearing on the body surface and/or with Vibrio sp. by immersing in the bacterial suspension. The number of F. marinus and other bacteria was taken count on the body surface and in the internal organs after the inoculation. Identification of bacteria other than F. marinus was performed on the predominant colonies that appeared on ager plates. Bacterial succession from F. marinus to Vibrio sp. was observed on the body surface in seriously diseased fish. The number of F. marinus decreased while that of Vibrio sp. increased gradually in the fish inoculated with both bacteria. Simple immersion in the suspension of Vibrio sp. increased the number of Vibrio sp. on the body surface but did not contribute to the advancement of the disease. Bacterial succession was not observed in the internal organs in any of the cases. From these results, it is suggested that the disease arises from the growth and invasion of F. marinus on the body surface and becomes serious by the successive invasion with Vibrio sp. on the same site.