The isolation, identification, and systematics of the motile Aeromonas species

Abstract

Our knowledge of the systematics of the aeromonads was in a state of confusion until recent genetic studies demonstrated that many more species of Aeromonas existed than had been previously realized. Because of studies performed using DNA-DNA hybridization, we presently recognize 14 genomospecies in which 10 have been named with hybridization group $\text{8}\text{10}$ (now combined) having two biovars. These findings suggest that correctly identified, individual species of Aeromonas could eventually be associated with particular signs and syndromes of fish diseases, as has been done to some extent with human Aeromonas-caused diseases. Considerable progress has been made, primarily with human isolates, in developing identification schema which show promise for accurately identifying the majority, if not all, of the Aeromonas spp. Rapid identification kits can be used to a limited extent in combination with manual methods. However, rapid methods alone are of limited benefit for identifying all of the species. Other methods are being used to further study the classification of Aeromonas sp. and to subtype Aeromonas sp. below the species level for epidemiological purposes. Many of these studies are using molecular approaches such as ribotyping, ribosomal RNA sequencing, isoenzyme analysis, DNA and RNA probes, and traditional serotyping. Lastly, there should be an avoidance of the dogma that if a system works for human isolates, it will work for fish and environmental isolates, also. There is a need to devise new systems and to evaluate the existing systems at different temperatures extensively using Aeromonas isolates from fish with the ultimate goal of achieving a reliable standard method for identification of Aeromonas fish isolates to the species level.