Identification and characterization of Vibrio bacteria isolated from fish and shellfish in Vietnam

A taxonomic relationship of thirty one Vietnamese bacterial isolates from different fish and shellfish together with twenty two reference strains was investigated by Euclidean distance with unweighted average linkage clustering. Comparison based on fourty seven phenotypic characters showed that these isolates mainly clustered in six groups of which four were equated with the well known Vibrio species, V. alginolyticus, V. harveyi, V. cholerae and V. mimicus. For the remaining two groups comprising twelve isolates, it was more difficult to establish any relationship with known species when compared with reference strains. Strains were also subjected to rRNA gene restriction pattern analysis (ribotyping), using Mlu I as restriction enzyme. Eleven ribotypes were detected among the Vietnamese isolates. Similarity of ribotyping patterns between strains supported the phenotypic identification. Twenty-eight strains were found to carry at least one plasmid and 12 different sized plasmids were detected ranging from less than 2 to 140 kb. The two Vibrio spp. groups performed high phenotypic and genotypic similarity within each group but were only remotely related with the reference strains. The evidence suggest that these strains may represent new Vibrio species

Involvement of a sialic acid-binding lectin with hemagglutination and hydrophobicity of <em>Flavobacterium psychrophilum</em>

Strains of Flavobacterium psychrophilum were studied for their ability to adhere and cause agglutination of erythrocytes and yeast cells. Strains of the serotype Th showed low or no hemagglutinating (HA) properties toward human, avian, bovine, and rainbow trout erythrocytes, whereas strains of serotype Fd and Fp(T) exhibited distinct HA properties. None of the strains was able to cause agglutination of yeast cells. Greater adherence specificity toward rainbow trout blood cells was seen for the HA-positive strains. Growth at 5°C, compared to that at 15°C, induced an increase in the hemagglutination of some strains. HA activities of F. psychrophilum were inhibited only by sialic acid (N-acetyl-neuraminic acid), heat treatment at 65°C, and proteinase K treatment and not by any of seven other carbohydrates, periodate oxidation, or treatment with trypsin. The supernatant from washed bacterial cells also showed some HA properties. All strains were shown to be highly hydrophobic by the hydrophobic interaction chromatography test, although some contradictions to the results of the salt aggregation test (showing some strains as less hydrophobic) were seen. These results indicate that the aggregation of F. psychrophilum and erythrocytes depend on a lectin present on the surface of HA-positive F. psychrophilum strains and absent on HA-negative strains. This lectin reacts specifically with sialic acid. The adhesion differences observed for F. psychrophilum strains do not appear to correlate with the virulence but still provide insights into the interaction of F. psychrophilum and rainbow trout