Paradeontacylix buri n. sp. is described based on specimens from the afferent branchial arteries of the Japanese amberjack Seriola quinqueradiata cultured in Mie and Oita Prefectures, Japan. The new species can be differentiated from congeners by a body of up to 4.15 mm with lanceolate tegumental spines of the same size throughout the body, uterus ascending after leaving the oötype and the vitellarium not extending posterior to the ovary. P. buri n. sp. is unique among Paradeontacylix species from Seriola spp. in having the same size tegumental spines throughout the body. A phylogenetic analysis based on the sequences of the internal transcribed spacer 2 and on the 28S rRNA-gene demonstrated that P. buri is grouped with other Paradeontacylix species from Seriola spp., indicating that the enlarged tegumental spines in the posteriormost rows in the other Paradeontacylix spp. from Seriola spp. are not a morphological feature at the generic level. Another blood fluke, Paradeontacylix sp., is described based on a single specimen from the afferent branchial artery of yellowtail amberjack S. lalandi cultured in Oita Prefecture, Japan. This species may be differentiated from the most similar P. buri n. sp. by the cirrus (conical and thick walled in Paradeontacylix sp. vs. spherical and thin-walled in P. buri) and by the uterus (extending posteriorly up to the level of the oötype vs. extending posterior to the oötype).
Streptococcus parauberis is a pathogen of streptococcosis in turbot Scophthalmus maximus and the Japanese flounder Paralichthys olivaceus. S. parauberis isolates from diseased Japanese flounder have been classified into several serological phenotypes. In this study we analyzed the DNA sequence of the genetic locus for capsular polysaccharide (CPS) biosynthesis of S. parauberis KRS02083 (subserotype Ia), NUF1003 (subserotype Ib), NUF1071 (subserotype Ic), NUF1032 (serotype II), 2007-1 (nontypeable/PFGE cluster I) and NUF1095 (nontypeable/PFGE cluster III) to elucidate the genetic basis for serological diversity. As a result, three kinds of cps locus were revealed among serotypes and subserotypes, namely the loci for subserotype Ia, subserotypes Ib/Ic and serotype II. The genetic structure of cps loci suggests that the capsules of S. parauberis are synthesized through the Wzy-dependent pathway. Subserotypes Ib and Ic possessed the same genetic structure, although single-base substitution at several regions or insertion of an IS (insertion sequence) element was found in subserotype Ic. The nontypeable strains, which agglutinated with both serotypes I and II antisera, possessed the same genetic structure as subserotype Ib/Ic or serotype II with single-base substitution at several regions.
Since 2012, Lactococcus garvieae strains which do not agglutinate with anti-KG– phenotype rabbit serum have been isolated from cultured yellowtail Seriola quinqueradiata and greater amberjack S. dumerili in Japan. In this study, pathogenicity of non-agglutinating L. garvieae was confirmed by intraperitoneal injection into these fish species. Cross-protective responses of yellowtail to the KG– phenotype and non-agglutinating strains were also examined. Yellowtail were immunized with formalin-killed cells (FKC) prepared from both types. Three weeks after immunization, the fish were challenged with the KG– phenotype and non-agglutinating strains. Each type of FKC provided effective protection against infection with the homologous strain. The protection level of the KG– phenotype FKC was relatively lower against the non-agglutinating strain than against the homologous KG– phenotype and the non-agglutinating type FKC was ineffective against the KG– phenotype. In conclusion, we propose two serotypes (I and II) of L. garvieae isolated from marine fish species in Japan. Serotype I which agglutinates with anti-KG– phenotype serum is typical L. garvieae and divided into Ia and Ib, which are KG– (capsulated) and KG+ (non-capsulated) phenotypes, respectively. Serotype II which does not agglutinate with the anti-KG– serum is a new type in fish pathogenic L. garvieae.
Edwardsiella tarda causes a serious disease known as edwardsiellosis in farmed freshwater and marine fishes. We previously reported that the hemagglutination and cell adherence activities of E. tarda increase in high-salt culture conditions (3% NaCl). This paper describes the induction of fimbriae expression in E. tarda in such high-salt (3% NaCl) culture conditions, using two different phenotypic strains of E. tarda, FK1051 (motile) and MEE0309 (non-motile), isolated from diseased fish. Both strains exhibited faster growth in liquid medium supplemented with 0% to 2% NaCl and slower growth in the 3% NaCl conditions. Hemagglutination activity against guinea pig erythrocytes was detected only in the 2% NaCl and/or 3% NaCl cultures. Electron microscopy revealed two types of fimbriae. The first type was thick (ca. 9 nm) and appeared only in the 0% NaCl culture of FK1051, and the second type was thin (ca. 4 nm) and appeared in the 3% cultures of both strains. The expressions of the major fimbrial subunit gene (etfA) in both strains were significantly higher in the 3% NaCl cultures than in the 0% NaCl cultures. The present results suggest that the thin type of fimbriae is involved in the cell adherence of E. tarda.
A multiplex PCR assay for differentiation of Streptococcus parauberis serotypes was developed. The three primer pairs for subserotypes Ia and Ib/Ic and serotype II were designed from the serotype-specific sequences of the wzy gene in the loci for capsular polysaccharide biosynthesis. All of 188 S. parauberis isolates from Japanese flounder showed positive reaction with the expected size of PCR product for each serotype, which was consistent with the results of agglutination test using rabbit antisera. The nontypeable isolates, which are not differentiated by agglutination test, could be identified as subserotype Ib/Ic or serotype II. Other streptococci including S. parauberis derived from cow and major bacterial fish pathogens showed negative reaction.