Pathogenicity of Vibrio splendidus biovar II, the causative bacterium of bacillary necrosis of Japanese oyster larvae.

Abstract

The potential pathogenicity of strains of Vibrio splendidus biovar II, which were isolated from bacillary necrosis of triploid larvae of Pacific oyster Crassostrea gigas in a hatchery in western Japan, was investigated.The course of experimental infection with virulent strains of V. splendidus biovar II was very rapid in 5-day-old veliger larvae with disease signs apparent within 6 to 12 h after exposure of larvae at doses of 104 to 106 CFU/ml, and mortalities up to 100% were recorded in 24 h at 105 and 106 CFU/ml.Although all the tested stages of larvae were experimentally infected by virulent strains of V. splendidus biovar II, a later stage (17 days posthatching) was less susceptible than the earlier stages of development. Diploid and triploid larvae were almost equally susceptible to this pathogen.Extracellular products and intracellular components of the strains were lethal to larvae, but their lethality did not correlate with the virulence of live cultures.These results suggest that the ability to elaborate toxins is not the only virulence factor in the pathogenicity of V. splendidus biovar II. The ability of this pathogen to bring about significant mortalities in oyster larvae at densities of 104 CFU/ml and its long survival in seawater make this pathogen a potential threat to larval oyster productions in hatchery systems.

TetR-Type Transcriptional Regulator VtpR Functions as a Global Regulator in Vibrio tubiashii

“…Although the VtpB protein contains some of features typically found in metalloproteases, VtpB is clearly distinct from the VtpA-type of metalloproteases in terms of size as well as amino acid sequence. It is interesting that V. splendidus, V. campbellii, and V. harveyi, all of which are known shellfish pathogens (14,16,44), carry homologs of vtpB, whereas other pathogenic Vibrio species do not. This correlation implies that the VtpB type of metalloproteases might play a role in shellfish diseases.…”

Vibriostatic Bacteria Isolated from Rearing Seawater of Oyster Brood Stock: Potentiality as Biocontrol Agents for Vibriosis in Oyster Larvae.

“…in some hatcheries has also increased, although the occurence of vibriosis in larvae is a little known case. However, mass mortalities in the cockle Fulvia mutica and in C. gigas larvae caused by vibriosis have been reported from hatcheries in Japan (Fujiwara et al,1993;Sugumar et al, 1998a).…”

The Extracellular Metalloprotease ofVibrio tubiashiiIs a Major Virulence Factor for Pacific Oyster (Crassostrea gigas) Larvae

“…Culture supernatants of V. cholerae carrying vtpA but not vthA were highly toxic to Pacific oyster larvae. Together, these results suggest that the V. tubiashii extracellular metalloprotease is important in its pathogenicity to C. gigas larvae.Vibriosis caused by marine Vibrio species is considered one of the most serious diseases of hatchery-reared oyster larvae (10,11,17,47,52). The disease is characterized by a rapid and dramatic reduction in larval motility, detached vela, and necrotic soft tissue, which lead to high mortality rates, exceeding 90% within 1 day of infection (45).…”

“…Vibriosis caused by marine Vibrio species is considered one of the most serious diseases of hatchery-reared oyster larvae (10,11,17,47,52). The disease is characterized by a rapid and dramatic reduction in larval motility, detached vela, and necrotic soft tissue, which lead to high mortality rates, exceeding 90% within 1 day of infection (45).…”