Studies On The Bacterial Infection And Its Pathogen Of Crab (Eriocheir Sinensis L.)

Diseases(No.1 and No.2) of one year crab(Eriocheir sinensis L.) were examined,which occurred in two farms of Qinhuangdao and Tangshan of Hebei province,the results showed that two cases belonged to bacterial septicaemia infection,and No.1 were mixed infected by Vibrio anguillarum of Vibrio(Pacini 1854),Aeromonas veronii of Aeromonas(Kluyver and van Niel 1936) and Citrobacter freundii of Citrobacter(Werkman and Gillen 1932);No.2 were singly infected by Vibrio anguillarum.The phenotypic information of 24 pure cultures of three species,including morphological characteristics,physiological and biochemical characteristics,and the G+C ratio of the DNA for representative strains,were studied extensively.In addition,molecular identification analysis of the nucleotide sequence of the 16S rRNA gene was applied,the 16S rRNA gene were partially sequenced and compared with sequences deposited in databases,and the phylogenetic tree representing genetic relatedness among the isolates and publicly available 16S rRNA gene sequence from GenBank database was constructed.Twelve strains of V.anguillarum(six strains from No.1:HQ0105016A-1 to HQ0105016A-6,six strains from No.2:HF010522-1 to HQ010522-6),six strains of A.veronii (HQ0105016B-1 to HQ0105016B-6),six strains of C.freundii(HQ0105016C-1 to HQ0105016C-6) were examined;16S rRNA gene sequence of selected representative strain (HQ0105016A-1 and HQ010522-1 from V.anguillarum,HQ0105016B-1 from A.veronii, HQ0105016C-1 from C.freundii) was detected,the results indicated that the sequenced 16S rRNA gene of strain HQ0105016A-1(GenBank accession no.DQ068758) is 1423 bp in length;the sequenced 16S rRNA gene of strain HQ010522-1(GenBank accession no. DQ068759) is 1420 bp in length;the sequenced 16S rRNA gene of strain HQ0105016B-1 (GenBank accession no.DQ010114) is 1413 bp in length;the sequenced 16S rRNA gene of strain HQ0105016C-1(GenBank accession no.DQ029351) is 1420 bp in length.The clinical signs and pathological changes of two cases of crab were examined; examinations of immune serology were conducted including the slide agglutination tests and indirect fluorescent antibody technique,using the rabbit antiserum raised against the selected representative strains,showed the serum homology of examined pathogenic bacteria. Artificial infection experiments of representative strains to healthy crab were conducted,the results showed the corresponding primitive causal agent of the diseases.The examination technology was constructed in characteristics of diseases,isolation and identification of pathogen,and examination of immunology in this studies.The score of drug resistance was clarified by susceptibility tests of isolates.The results were the references in the examination of pathogen and control of bacterial septicaemia infection of crab.