Search

Lactobacillus L15, a strain of Lactobacillus sp. isolated from the intestinal tract of healthy Paralichthys olivaceus, and Lactobacillus acidlophilus ATCC4356 were used to investigate their specific adhesions. It was shown that cell surface proteins of two strains could be extracted by 5 mol/L lithium chloride( LiCl). Two surface proteins with molecular weights of 61.8 kDa and 54.6 kDa were identified to mediate the adhesion to intestinal mucus of Paralichthys olivaceus and Common carp respectively by the method of Western blotting, and the two novel proteins were named as MAPPpo1 and MAPPcc. In Lactobacillus acidlophilus ATCC4356, two proteins of 43.0 kDa and 63.3 kDa were identified to mediate the adhesion to intestinal mucus of Paralichthys olivaceus. Nevertheless, only 43.0 kDa protein was identified to mediate the adhesion to intestinal mucus of Common carp. Furthermore, the mucus proteins which participated the adhesion as the bacteria receptors were identified by the same method and it was found that L15 and ATCC4356 had the same receptors.There were 29.7 kDa and 30.3 kDa proteins in the intestinal mucus of Paralichthys olivaceus and only the 26.2 kDa protein was testified in the intestinal mucus of Common carp. It is demonstrated that the adhesion of Lactobacillus to mucus is dependent on the strain specificity, as well as host specificity.

An outbreak of ulcer disease of the cultured turbot Scophthalmus maximus L. occurred in an indoor farm in Haiyang, Shandong Province in the sweltering August of 2004 and caused significant mortality. At the beginning, infected turbots displayed sluggish swimming and anorexia. Several days later, the turbot eyes swelled, the fins and tail turned red, and the back gradually ulcerated. Dissection of the moribund fish showed that the ulcerative gills paled, the liver becamed bloodshot, the kidney and gallbladder swelled, the intestinal wall became filmy and bloodshot. The time course from appearance of disease signs to death lasted about a week. A dominant strain of bacteria, which was Gram-negative and short rod with single polar flagellum under electron microscope, was isolated from the diseased turbot and designated as H1. In artificial infection test, all fish of the experimental groups died in a week after intramuscularly injected with bacterial suspension, while the control group showed no signs in 10 d post-challenge. The moribund experimental fish had similar gross signs as the natural infected fish. The bacteria re-isolated from the challenged fish also had the same characteristics as H1, which proved that the isolate H1 was the pathogenic bacteria that triggered this ulcer disease. Different methods were used to identify the pathogenic bacteria. The identification result by API 20NE and API 20E system indicated that H1 was Aeromonas hydrophila, with 99% reliability and 61.5% respectively. While traditional biochemical identification revealed that H1 exhibited relatedness to Vibrio harveyi. In order to confirm the different result, a 1424 bp sequence of H1's 16S rDNA was amplified and compared with other Vibrio spp. in GenBank, homology analysis and phylogenetic study showed that H1 has the highest similarity to V. harveyi, with 99% identity. According to morphological features, physiological and biological characteristics and 16S rDNA homology comparison of the bacteria, the pathogenic bacteria were V. harveyi. Drugs sensitivity test showed that the pathogenic bacteria were highly sensitive to nitrofurantoinum and ceftriaxone sodium etc. This is the first report that V. harveyi was found as the pathogenic bacteria of cultured turbot in China. The research suggests that V. harveyi should be regarded as an important pathogen of turbot and can causes ulcer disease under conditions of high temperatures. Therefore, it is necessary to prevent against ulcer disease in culture turbot in summer.