We developed a liposome vaccine in which Aeromonas hydrophila antigens were entrapped within the liposomal membrane compartment. Oral administration of the vaccine was found to immunize common carp Cyprinus carpio (mean body weight, 30 g) against A. hydrophila. Two fish groups received the liposome vaccine (protein concentration, 33 μg/mL) at doses of 10 and 30 μL/fish/day for a period of 3 days. The levels of antibodies in the serum rose at 2 and 3 wk post vaccination (p.v.) and then declined at 4 wk p.v.. When fish groups orally immunized with a total of 30 μL/fish for 3 days were challenged by an intra-subcutaneous injection with live A. hydrophila at a dose of 3.0×105 or 1.0×106 CFU/fish at 22 days p.v., the fish were protected against the bacterial infection with RPS of 63.6 or 55.0%, respectively.
A benedeniid parasite infecting the body surface of cobia Rachycentron canadum cultured in net cages in Taiwan was identified as Neobenedenia girellae. This is the first confirmed case of N. girellae infection of marine fish from Taiwan. N. girellae was not randomly distributed on the host; it concentrated on the dorsal side of the head area (59.7%), especially on the eyes (23.7%), while it was less frequent on the ventral side and not detected on the fins. N. girellae caused considerable histological damage to the host through the attachment by the haptor and possibly through feeding activity by the pharynx. In infected eyes, epithelial cells of the cornea were often partially lost, and the collagenous stroma was considerably thickened and edematous, associated with massive inflammatory cell infiltration.
Streptococcus iniae is known as an important marine and freshwater fish pathogen worldwide. In this paper, we characterized two serological phenotypes in Japanese S. iniae isolates, mainly from Japanese flounder Paralichthys olivaceus. The two phenotypes, designated K+ and K-, were distinguished by the presence or absence of capsule. K- cells agglutinated both with anti-K- and K+ type sera, whereas K+ cells agglutinated only with anti-K+ type serum. These two types were indistinguishable by any ordinary biological or biochemical characterization tests. Immunodiffusion test demonstrated the common antigens and a K+ type-specific antigen in the autoclave-extracts of cells. Capsule was observed on the K+ cells, from which acidic polysaccharides were detected. Strains of K+ type were virulent for Japanese flounder, whereas those of K- type were avirulent. There is a direct relationship between the serological phenotypes and the existence of capsule in S. iniae with link to its virulence.
Flavobacterium psychrophilum can be classified into two genotypes, A and B, by the polymorphism in an unexpected product of 290 bp that is amplified with universal primers for gyrase subunit B gene. We identified the 290 bp fragment as a part of coding region of peptidyl-prolyl cistrans isomerase C (PPIC) gene. Using PCR newly designed for PPIC gene, specific amplification was observed in all F. psychrophilum strains tested, and no amplification occurred in any other bacterial species tested. Moreover, genotype A was found only in isolates from ayu Plecoglossus altivelis.
To study a possible quinolone resistance mechanism in Vibrio anguillarum, we examined gyrA and parC mutations among the oxolinic acid-resistant strains and laboratory-derived mutants. One point mutation only in the quinolone resistance-determining region (QRDR) of the gyrA gene was detected in one strain isolated from ayu Plecoglossus altivelis and laboratory-derived mutants with low-level resistance. On the other hand, point mutations in both the gyrA and parC QRDRs were detected in one strain isolated from ayu and a laboratory-derived mutant with high-level resistance. These results suggest that as in other Gram-negative bacteria GyrA and ParC are the primary and secondary targets, respectively, of quinolone in V. anguillarum.
A Gram-negative rod-shaped bacterium was isolated from diseased Japanese flounder Paralichthys olivaceus (mean total length, 33 mm), during a disease outbreak in a flounder hatchery in Fukui Prefecture, Japan in 2005. The isolated bacterium produced water-soluble brown pigment and was identified as Vibrio anguillarum serotype A (J-O-1) by biochemical and serological tests, and 16S rDNA sequence. The pathogenicity of the isolated bacterium to Japanese flounder was confirmed by intraperitoneal injection, but not by bath immersion. This is the first report of isolation of brown pigment-producing V. anguillarum.
Mass mortality of carp Cyprinus carpio caused by koi herpesvirus disease (KHVD) occurred in seven rivers of Kanagawa Prefecture in 2004. Mortalities of KHVD peaked in May in four of the rivers (early outbreak group) and peaked in June in the other three rivers (late outbreak group). KHVD was first recognized at 15.5-18.5°C in the early outbreak group, and at 18.6-21.2°C in the late outbreak group. The temperature exceeded 15°C, which corresponds to the lowest temperature of the viral growth in cell culture.