Protection against atypical Aeromonas salmonicida infection in common carp, Cyprinus carpio L., by oral administration of a mixed microbial culture of Lactobacillus paracasei, Pichia membranifaciens and Saccharomyces cereviciae.

A microbial culture was prepared by co-cultivation of Lactobacillus paracasei, Pichia membranifaciens and Saccharomyces cereviciae for 48 hr at 30°C in rice bran extract medium, supplemented with dextrose. Oral administration of the resulting non-viable heat-inactivated microbial culture to common carp, Cyprinus carpio L., delivered in feed for four weeks, induced effective protection against experimental atypical Aeromonas salmonicida infection which causes "ulcer disease". After challenge of the carp by immersion, fish mortality and development of skin lesions such as hemorrhages and ulcers were significantly suppressed in carp treated with mixed microbial culture adsorbed on dry pellets relative to carp treated with medium or without extract. Atypical A. salmonicida was re-isolated from ulcerative lesions in parts of dead and surviving fish, but Aeromonas hydrophila and Flavobacterium sp. were also isolated from these fish, verifying microbial population changes during the progression of skin lesions. Among interleukin-1β (IL-1β), tumor necrosis factor-α, as well as CXC-α and CXC-β chemokines, gene expression of IL-1β was up regulated in the spleen and head kidney three weeks after administration of the mixed microbial culture. These results clearly show that this mixed microbial culture, delivered in feed, is effective in preventing A. salmonicida disease in carp.