Studies On The Pathogenicity Of Pseudomonas Plecoglossicida Isolated From Pseudosciaen Crocea

In recent years,with the development of the mass farming,visceral whitespot disease causing by P.plecoglossicida have become a common disease in cage culture of P.crocea and caused considerable economy loss.P.plecoglassicida NZBD11 is typical of the pathogens,prevalent only at the water temperature 16°C to 20°C.Temperature have an effect on its pathogenicity When the water temperature at 18°C will lead to the visceral white spot occurrence,it natural fades after the water temperature is more than 28°C or less than 15°C.So hypothermy nonpathogenic temperature 12°C,high pathogenic temperature 18°C and hyperthermy nonpathogenic temperature 28°C as the experimental temperature has typical significance.The research results of this paper could improve the understanding of pathogenesis of P.crocea visceral white spot disease.In this paper,ECP was prepared by the cellophane plate technique.After preliminary detecting,we discovered that there was protease(serine proteinase,cysteine proteinase,aspartic proteinase,pepsin-like,chymotrypsin-like),amylase,lecithinase and acid-phosphatase,alkaline-phosphatase activity in the ECP,and no gelatinases,lipase,urease and metalloproteinases activity.In addition there was little hemolysis activity for sterile defibrinated sheep blood cells.The NZBD11 was cultivated at three different culture temperature(12?C,18?C and 28?C)to prepare their ECPs and we studied the effect of culture temperature on enzymatic activity and hemolysis activity.The cysteine protease,aspartic protease,serine protease,pepsinase-like,chymase-like and lecithinase had higher enzyme-activity at 18°C than other two culture temperature.And we inferred that those enzymes were virulence factors;aminopeptidase,acid-phosphatase,alkaline-phosphatase activity and hemolysis activity were almost not affected by culture temperature.The SDS-PAGE showed that the prepared ECP had various protein electrophoresis pattern,especially 50 kDa,43 kDa and 28 kDa.It is closely related to the pathogenicity of the bacteria.The P.plecoglassicida were cultured at high pathogenic temperature and its ECP was prepared by the cellophane plate technique.The enzyme activities of ECP were measured under different temperature(hypothermy nonpathogenic temperature 12°C,high pathogenic temperature 18°C and hyperthermy nonpathogenic temperature 28°C).The results showed that the activities of amylase,serine proteinase,aspartate proteinase,pepsinase-like,chymotrpsin-like,lecithinase,acid phosphatase and alkaline phosphatase of ECP of P.plecoglassicida were affected by temperature notably,and under the condition of 28°C their activities were significantly higher than 12°C or 18°C(P<0.05)while the enzymatic activities of cysteine proteinase,aminopeptidase and hemolysis activity were not significantly changed(P>0.05).Although the ECP is one of the pathogenic factors,the results of this paper revealed that P.crocea visceral white spot disease had high incidence at specific temperature interval(16~20°C)not because ECP possess higher activity at this temperature interval.Combined with previously experiments,it suggested that the protease activities(aspartic proteinase,pepsin-like,chymotrypsin-like,serine proteinase,cysteine proteinase and lecithinase)under the condition of 18°C were not significantly higher than 12°C or 28°C.The results of this paper revealed that the mechanism of visceral white spot disease is complex.And it is not limited to ECP enzyme activities.