Aeromonas hydrophila subsp. ranae subsp. nov., isolated from septicaemic farmed frogs in Thailand.

A group of seven sucrose-negative Aeromonas strains (referred to as group Au) isolated from the internal organs of septicaemic farmed frogs (Rana rugulosa) in Thailand was subjected to a polyphasic taxonomic study including fluorescent amplified fragment length polymorphism (FAFLP) and ERIC-PCR fingerprinting, 16S rDNA sequencing, microplate DNA-DNA hybridizations and extensive phenotypic characterization. Comparison of FAFLP and ERIC-PCR fingerprints indicated that the group Au isolates belonged to the species Aeromonas hydrophila DNA hybridization group (HG) 1 in which they represent a genotypic subgroup closely affiliated to A. hydrophila subsp. hydrophila and subsp. dhakensis. One representative of the Au group exhibited > or = 99.0% 16S rDNA sequence similarity with the type strains of the two A. hydrophila subspecies. DNA-DNA hybridization with type and reference strains of all known Aeromonas taxa revealed that the Au group represented a homogeneous taxon that exhibited the highest relatedness with members of the two A. hydrophila subspecies, ranging from 75 to 93%. Phenotypic characterization on the basis of 152 features further revealed that the Au group isolates differed from A. hydrophila subsp. hydrophila or subsp. dhakensis in a total of 13 biochemical properties. Of these, assimilation of L-glycine and isobutyrate as sole carbon source, acid production from salicin and D-sucrose, and aesculin hydrolysis were of diagnostic value. From the results of this study, it can be concluded that the Aeromonas frog isolates of the Au group represent a new subspecies of A. hydrophila, for which the name Aeromonas hydrophila subsp. ranae subsp. nov. is proposed. Its type strain is Au-1D12(T) (=LMG 19707(T) = CCUG 46211(T)).

Aeromonas hydrophila subsp. dhakensis subsp. nov., isolated from children with diarrhoea in Bangladesh, and extended description of Aeromonas hydrophila subsp. hydrophila (Chester 1901) Stanier 1943 (approved lists 1980).

A group of 10 Aeromonas hydrophila-like strains referred to as group BD-2, which mainly comprised haemolytic and cytotoxic isolates from diarrhoeal children in Bangladesh, was subjected to a polyphasic taxonomic study including fluorescent amplified fragment length polymorphism (FAFLP) and ERIC-PCR fingerprinting, microplate DNA-DNA hybridization and extensive phenotypic characterization. Comparison of FAFLP and ERIC-PCR genotypic profiles indicated that the group BD-2 isolates constituted a separate taxon that was most closely related to A. hydrophila DNA hybridization group (HG) 1. Determination of DNA-DNA hybridization values with type and reference strains of all known Aeromonas taxa revealed that the BD-2 group represented a homogeneous taxon (internal DNA homology, 77-94%) that exhibited 78-92% DNA relatedness with the type strain of A. hydrophila HG1. These results indicated that the BD-2 group belongs genotypically to A. hydrophila HG1, but examination of 152 phenotypic characteristics revealed that the group BD-2 isolates differed from representatives of HG1 in eight biochemical properties. The diagnostic value of at least three of these tests, namely utilization of urocanic acid and L-arabinose and acid production from L-arabinose, has been confirmed outside this study by other workers. Collectively, the genotypic and phenotypic data reported suggest that the BD-2 group represents a subspecies of A. hydrophila, for which the name Aeromonas hydrophila subsp. dhakensis subsp. nov. is proposed. Its type strain is P21T (= LMG 19562T= CCUG 45377T). An extended description of A. hydrophila subsp. hydrophila (Chester 1901) Stanier 1943 (Approved Lists 1980) is given.

Vibrio trachuri Iwamoto et al. 1995 is a junior synonym of Vibrio harveyi (Johnson and Shunk 1936) Baumann et al. 1981.

The taxonomic position of Vibrio trachuri was examined through a polyphasic approach using 16S rDNA sequencing, fluorescent amplified fragment length polymorphisms (FAFLP), DNA-DNA hybridization experiments, G+C content of DNA and phenotypical tests. Phylogenetic analysis showed that Vibrio harveyi is the closest neighbour of V. trachuri, sharing about 98.8% similarity in the 16S rDNA gene. Moreover, numerical analysis of the FAFLP patterns revealed that both species have highly related genomes, sharing 55% pattern similarity. DNA-DNA hybridization experiments and G+C content measurements reinforced these results, since V. trachuri and V. harveyi had at least 74% DNA similarity and 44.5-45.2 mol % G+C. Phenotypical features of both species were also very similar, except that V. trachuri utilized itaconic acid, whereas V. harveyi did not. Therefore, it is proposed that the species V. trachuri should be reclassified as V. harveyi.

DNA-DNA reassociation and phenotypic data indicate synonymy between Aeromonas enteropelogenes Schubert et al. 1990 and Aeromonas trota Carnahan et al. 1991.

Mainly on the basis of phylogenetic and genotypic evidence, it has been suggested previously that the species Aeromonas enteropelogenes Schubert et al. 1990 is identical to the species Aeromonas trota Carnahan et al. 1991. Probably because the description of A. enteropelogenes preceded the proposal of A. trota by only a few months, DNA-DNA hybridizations were never performed between representative strains of these two taxa. In the present study, new DNA-DNA hybridizations between the type strain of A. enteropelogenes, LMG 12646(T) (= DSM 6394(T)), and reference strains of A. trota, including its type strain LMG 12223(T)(= ATCC 49657(T)), showed a genomic relatedness of 81-99%. In addition, phenotypic characterization revealed that the two type strains exhibited identical API 20E and API 50CHE biochemical profiles and were both susceptible to ampicillin and carbenicillin. Collectively, our new DNA reassociation and phenotypic data confirm previous taxonomic data that indicate that the taxa A. enteropelogenes and A. trota are synonymous members of the same Aeromonas species. Although the species name A. enteropelogenes has nomenclatural priority, the authors would like to discourage the use of this name because the name A. trota has been cited much more frequently. The preferential use of A. trota in future publications may be the best option to avoid ambiguity in the description of ampicillinsusceptible aeromonads and to secure nomenclatural continuity in Aeromonas literature.