Aeromonas hydrophilaがコイの筋肉内で産生するα溶血性毒素

Toxins produced by Aeromonas hydrophila strain A10 in the muscle of carp at the site of injection were studied. Carps injected with the crude toxins showed swelling and reddening of the body surface as those injected with the live bacteria. The toxic substance was partially purified from a extract of the necrotized muscles by ammonium sulfate precipitation, ion-exchange chromatography and gel filtration. As a result, it was suggested that α-type hemolysin was implicated in the toxicity. The hemolysin was heat-labile, and inactivated by EDTA, trypsin and papain, but stable at pH value between 4.0 and 11.2

Structural characterization of Tn916-like element in Streptococcus parauberis serotype II strains isolated from diseased Japanese flounder.

AIMS: To screen for the existence and determine the structure of Tn916-like element in Streptococcus parauberis serotype II strains isolated from cultured Japanese flounder in western Japan. METHODS AND RESULTS: In this study, the structure of Tn916-like element and the flanking regions were characterized by polymerase chain reaction (PCR) and inverse PCR, followed by cloning and sequencing. The Tn916-like element is 18 031 bp in length and composed of 22 ORFs. Southern blot hybridization analysis showed that the HincII-digested internal structures of Tn916-like elements yielded two patterns among S. parauberis serotype II strains. The flanking sequences were identical with the corresponding region of S. parauberis serotype I strain except for the addition of 6-bp coupling sequence (ATCATA) being adjacent to the upstream of the element. CONCLUSION: The Tn916-like element exhibited high homology (more than 99%) with Tn916 observed in other streptococci and enterococci and was integrated in the same site of chromosome for all of the tested S. parauberis serotype II strains. SIGNIFICANCE AND IMPACT OF THE STUDY: The results indicate that the Tn916-like element encoding tet(M) gene is present in all of the tested S. parauberis serotype II strains, which are disseminated in the flounder-culturing areas in western Japan.The definitive version is available at www.blackwell-synergy.co

実験的 Streptococcus iniae 感染ヒラメの発病過程に関する免疫組織化学的検討

To investigate the course of Streptococcus iniae infection in Japanese flounder Paralichthys olivaceus, fish (average weight 118±14 g) were experimentally infected by oral and bath methods, and the distribution and multiplication of S. iniae in the fish were monitored by bacteriological and immunohistochemical examinations. S. iniae was detected first in relatively high numbers in the kidney and spleen. Viable counts of S. iniae in the blood, brain, liver, stomach, intestine, gill, skin mucus and nares were high only when those in the kidney and spleen were high. S. iniae-Iaden phagocytic cells were observed in the lumen of the blood vessels distributing in the organs and tissues in the initial stage of infection. Many fish showed hemorrhagic lesions on the fins, and the extracellular multiplication of S. iniae in the hemorrhagic fins was observed in the initial stage of infection. These observations were common among the fish challenged by either method. There was no evidence of the entrance of S. iniae through the stomach, intestine, gill, eye or olfactory pouches of nares. It was presumed that S. iniae entered directly from the water through the abrasive sites of fins and was disseminated by the blood circulation to cause systemic infection

ヒラメレンサ球菌症の実験感染

The capability of Streptococcus iniae to cause disease in Japanese flounder was investigated by oral and bath (30 min) challenges with low, medium and high inoculation doses. Only with the highest inoculation dose, 9.9 x 10^7 CFU/100g body weight, the oral challenge induced deaths. In the bath challenge deaths were induced even at the lowest inoculation dose, 2.9 x 10^3 CFU/mL water. Hemorrhagic lesions on the fins were observed in dead fish challenged by both methods. It is suspected that S. iniae entered through the body surface such as abrasive sites of the fins to cause disease

タイ類由来非定型 Edwardsiella tarda の血清学的性状

The serological relationships between a non-motile variant of Edwardsiella tarda isolated from sea breams, Pagrus major and Evynnis japonica, and typical strains of E. tarda isolated from Japanese eel, Anguilla japonica and Japanese flounder, Paralichthys olivaceus, were studied. Cross-absorption test revealed that all strains shared a similar O-antigen. Agglutination tests showed the presence of heat-labile antigens on the cell surface of the non-motile strains from sea breams. Immunoelectrophoretic analysis demonstrated the relatedness of cell surface antigens among the strains from various fish species. The possibility of usage of a common vaccine for edwardsiellosis among sea breams and other fish species is suggested

Existence of Subserotypes in Streptococcus parauberis Serotype I

Streptococcus parauberis is the etiologic agent of streptococcosis in Japanese flounder Paralichthys olivaceus. Two serotypes, termed serotypes I and II, are known among the Japanese S. parauberis isolates. In the course of serodiagnosis, we found several strains that did not agglutinate with rabbit anti-serotype I or II sera. In this study, we investigated the serological and genetic relationships among the stocked S. parauberis strains including the non-agglutinating ones using a newly prepared rabbit antiserum against a non-agglutinating strain (NUF1071) as well as previously prepared antiserotype I and II sera, and pulsed-field gel electrophoresis (PFGE). An antiserum cross-absorption test and microtiter agglutination test revealed that the serotype I was divided into three subserotypes, tentatively designated Ia, Ib and Ic. The non-agglutinating strains belonged to the subserotype Ic. Of the 104 serotype I strains, 6, 91 and 7 strains belonged to subserotypes Ia, Ib and Ic, respectively. Formalin-killed cells of subserotype Ia and Ic strains were agglutinated with the anti-subserotype Ia serum (so far being used as an anti-serotype I serum) and Ic serum, respectively. Subserotype Ib strains were agglutinated with both sera. In PFGE analysis, the stocked 188 S. parauberis strains were divided into three clusters corresponding to subserotypes Ib/Ic, Ia and serotype II

Edwardsiella tarda の赤血球凝集能に関与する線毛遺伝子群の同定

We determined the nucleotide sequence of a 8.6 kb DNA region containing etfA encoding a putative fimbrial major subunit from chromosomal DNA of Edwardsiella tarda KG8401 which expresses mannose-resistant hemagglutination (MRHA). This region contained three novel genes, etfBCD, at the downstream region of etfA. The deduced amino acid sequences of EtfABCD contained conserved fimbrial domains; fimbrial protein, fimbrial chaperone, fimbrial usher and fimbrial protein, respectively. Escherichia coli transformed with the cloned etf operon expressed MRHA and fimbriae that reacted with rabbit antiserum against the fimbrial major subunit of E. tarda, showing the implication of the fimbriae in the hemagglutination of E. tarda

Infection Kinetics of Tenacibaculum maritimum on the Abraded Skin of Japanese Flounder Paralichthys olivaceus

Tenacibaculum maritimum is the gliding bacterium that causes tenacibaculosis, an ulcerative disease in marine fish. In this study, we conducted a pathogenicity test to assess the effect of skin abrasion on the infectivity of gliding and non-gliding strains of T. maritimum, NUF1128 and NUF1129, respectively, and investigated the infection kinetics by enumeration and immunohistochemical observation of the adhered and proliferated T. maritimum on the abraded skin of Japanese flounder Paralichthys olivaceus. In the pathogenicity test, Japanese flounder whose dorsal skin was abraded with a cotton swab or blade or tip of dorsal fin was clipped with scissors were immersed for 30 min in seawater containing 106 CFU/mL of cultured NUF1128 or NUF1129 cells. As a result 100% mortality was achieved in the fish groups pretreated with blades or scissors followed by challenged with NUF1128. NUF1129 was unable to induce infection regardless of the treatments applied. The infection kinetic studies revealed that NUF1128 adhered more readily than NUF1129 to dermal connective tissues which were exposed by abrasion with blades and subsequently proliferated mainly in the dermal connective tissues and perimysium

Biological and Serological Characterization of a Non-gliding Strain of Tenacibaculum maritimum Isolated from a Diseased Puffer Fish Takifugu rubripes

Tenacibaculum maritimum is a Gram-negative, gliding marine bacterium that causes tenacibaculosis, an ulcerative disease of marine fish. The bacterium usually forms rhizoid colonies on agar media. We isolated T. maritimum that formed slightly yellowish round compact colonies together with the usual rhizoid colonies from a puffer fish Takifugu rubripes suffering from tenacibaculosis, and studied the biological and serological characteristics of a representative isolate of the compact colony phenotype, designated strain NUF1129. The strain was non-gliding and avirulent in Japanese flounder Paralichthys olivaceus in immersion challenge test and showed lower adhesion ability to glass wall in shaking broth culture and to the body surface of flounder. It lacked a cell-surface antigen commonly detected in gliding strains of the bacterium in gel immunodiffusion tests. SDS-PAGE analysis showed different polypeptide banding patterns between NUF1129 and gliding strains. Like gliding strains, NUF1129 exhibited both chondroitinase and gelatinase activities, which are potential virulence factors of the bacterium. These results suggest that some cell-surface components related to gliding and adhesion ability are implicated in the virulence of T. maritimum