Study On The Isolation, Indentification And Pathogensis Of Stenotrophomonas Maltophilia In Channel Catfish

Since 2004, there has been an outbreak of an acute epidemic disease of channel catfish (Ictalunes punctatus) in China. The main gross pathologic changes of diseased fish showed hyperaemia, hemorrhage and a lot of irregular, variably sized areas of depigmentation on the body surface, distension of abdomen, pale gill, swelling liver, kidney and spleen, ascite, bleed gastroenteritis, intussusception in rectum, and prolapse in some sick fish. The disease has caused large economical loss. In order to understand the pathogen and pathogenesy of the disease, the aetiology, pathology and virulence factors were studied.A pathogenic bacterium (CCF00024) was isolated from the kidney and liver of the diseased fish with acute epidemic disease. Artificial infection proved that the bacterium was the pathogen of the disease. Its morphological, physiological, biochemical characteristics and 16S rDNA sequence analysis were studied furthermore. The isolated strain is an aerobic, non-fermentative bacterium. The bacteria are gram negative, rods, with polar multi-flagella, Oxidase-negative, methyl-red-negative, lysine decarboxylase-positive, DNAase-positive, urease-positive, lipase-positive and protease-positive. The bacteria can't utilize most of sugars, except maltose and mannose. A phylogenetic tree was constructed by comparing the 16S rDNA sequences of the isolated strain (GenBank accession number AY970826) with other relative bacteria species in the GenBank databases. In the phylogenetic tree CCF00024, S. maltophilia 13637T, S. maltophilia MG958T, and S. maltophilia M5-1 constitute a branch. The similarity value between strain CCF00024 and those 5 strains S. maltophilia are 99.4-99.6%. According to morphological, physiological, biochemical characteristics and phylogenetic analysis, the isolated strain (CCF00024 ) is identified as S. maltophilia. The result of antibiotic sensitivity testing showed the bacterium was sensitive to Lomefloxacin, Sulfamethoxazole, Sulfafurazole, Thiamphenicol, Azithromyci , Doxycycline and resistant to ampicillin, Carbenicillin, Cefazolin, Cefaclor, streptomycin, Gentamicin,...