Effects of an inactivated bacterium injection on some immune factors in sea cucumber Apostichopus japonicas

The cultured sea cucumber(Apostichopus japonicus Liao)recently suffered from serious disease‘skin ulcer syndrome’which has caused massive losses.One bacterial strain was isolated from these naturally infected sea cucumber,which was the most dominant among the isolates.The bacterium was identified as Aeromonas sp. by morphological,physiological and biochemical tests and 16S rDNA sequence analysis.Challenge test proved that it was the causative pathogen associated with the disease.The bacterium were killed by formaldehyde and used as an inactivated vaccine to inject normal sea cucumber.The immune effects were shown as follows:the highest lysozyme activities were observed at 6 h post-injection in 3.9×10 8 CFU/mL group,and at 24 h post- injection in 4.7×10 7 CFU/mL group.The alkaline phosphatase(AKP)activities reached maximum at 48 h post- injection in 3.9×10 8 CFU/mL group,and at 96 h post-injection in 4.7×10 7 CFU/mL group.However,there was no significant difference in superoxide dismutase(SOD)between the experimental groups and the control group. In general,the inactivated bacterium could increase the immune effects on sea cucumber.In addition,as the concentration of the inactivated bacterium was higher,lysozyme and AKP activities could reach the maximum rapidly and significantly.But the increased activities could not last long.