| Nocardia spp. whose content in sea water is not high, is an opportunistic pathogenthat can infect a wide range of cultured fish and result in an extremely large economiclosses of aquaculture industry. This dissertation mainly study: cluster analysis on15strains of pathogenic N. seriolae isolated from fish, histopathological study on goldenpompano Trachinotus ovatus infected with N. seriolae, the pathogenic factor of N.seriolae, the effect of cruing of T. ovatus suffering from N. seriolae with drug, theLAMP detection of N. seriolae. The main results were showed as follows:1Cluster analysis on15strains of pathogenic N. seriolae from fishIn this paper,15strains of bacteria were isolated from2006to2012year from thesampling or censorship fish(eight species) suffering from sarcoidosis which were fromthe South China were phylogenetic analysis and cluster analysis. The result of thephylogenetic analysis indicated that the sequences of16S rDNA of15isolated strains,which shared similarity99%to that of the N. seriolae, had a close evolutionaryrelationship with member of the N. seriolae and could be grouped into2clusers. Theresult of the cluster analysis showed that15isolated strains could be divided into twogroups while T=23. Group1and2were respectively divided into two and foursubgroups while T=11. The results suggested that diversity existed among the15strainsof N. seriolae.2Histopathological study on golden pompano T. ovatus infected with N. seriolaeThe pathogen N. seriolae isolated from the focus of illed T. ovatus cultured onseawater cage in Yangjiang Zhapo were artificially infected back to the healthy T.ovatus. The challenged fish displayed that lots of white nodules with0.1-0.3cm indiameter were scattered in the spleen, kidney, liver, gill and heart. Observations byhistopathology showed that the spleen and kidney were hemorrhage and lymphocytosis;Renal tubule epithelial cell appeared denaturalization and necrosis; Fatty degenerationemerged in hepatocyte; Proliferation and fusion of the gill lamellar epithelial cells as acudgel；Myocardial cells were swelling, rupture, dissolution. The above research resultsare helpful for future studies of its pathogenesis and diagnosis.3Preliminary studied on the pathogenic factor of N. seriolae A500μg quantity of cord factor separated and purified from the strain N11YJ01inthe form of w/o/w emulsion was injected into the healthy T. ovatus. The granulomatouschange in the kidney, spleen, gills stained by hematoxylin-eosin were maximum at days7-14after the injection. This demonstrated that the cord factor from N. seriolae is toxicin the first time. The mycolic acids were also extracted, and the thin-layerchromatography detection results showed that: the points were separated completely andlegible after coloured. Structures of these mycolic acids were analyzed usingelectrospray ionization mass spectrometry. They differ in the length (40-66) andsaturation (0-3doule bonds) of their constituent fatty acids.4Rapid detection of N. seriolae by loop-mediated isothermal amplificationA set of four LAMP primers were designed based on the sequence of the rpoA of N.seriolae to develop a loop-mediated isothermal amplification (LAMP) assay fordetection of N. seriolae. The assay was optimized to the most optimal conditions:1:8outer primer concentration ratio,6mmol/L of Mg2+,1mmol/L of dNTP, at56.4℃for50min. The detection limit of N. seriolae culture by LAMP was9.8×102+CFU/mL andthe results showed that the LAMP was more sensitivity than PCR. Futhermore, Thisassay which is simple, efficient and low-cost procedure is expected to become avaluable tool for rapid detection and identification of N. seriolae.5Studies on cruing of T. ovatus suffering from N. seriolae with drugIn order to control Trachinotus ovatus caused by N. seriolae, the effects of cruing ofthis disease with enrofloxacin, erythromycin and florfenicol were studied. The resultsshowed that the better treatment effect of dosing on the first day after challenged anddosing on the fourth day after challenged were enrofloxacin and erythromycin,respectively; the protective rate of Trachinotus ovatus caused by N. seriolae was53.4%,30%and26.7%. |
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