DIVERSITY OF VIBRIO-ANGUILLARUM ISOLATES FROM DIFFERENT GEOGRAPHICAL AND BIOLOGICAL HABITATS, DETERMINED BY THE USE OF A COMBINATION OF 8 DIFFERENT TYPING METHODS

In the present investigation we have studied 260 presumed Vibrio angui llarum isolates from a wide range of habitats, using a combination of eight different typing methods. The aims of the study were to investig ate the diversity of V. anguillarum, as indicated by the use of combin ed typing, and to determine if strains with identical or similar chara cteristics were present in certain geographical locations, or in certa in fish species. We also present a simple numerical method to analyse data obtained from combined typing. Two hundred and sixty isolates nam ed as V. anguillarum from various fish species, rotifers, Artemia, wat er and sediment were subjected to the following eight assays: Species identification using ribotyping and the BIOLOG GN plates, subtyping us ing determination of outer membrane profiles, plasmid typing, serotypi ng, determination of lipopolysaccharide profiles and biotyping with AP I 20E, and biochemical fingerprinting with the PhenePlate system. The diversity among all isolates, calculated as Simpson's diversity index (Di), varied between 0.19 (ribotyping), i.e. most isolates belonged to the same type, and 0.98 (PhP), i.e. most isolates different. Upon com bination of all methods, where a difference between two strains in at least two methods was regarded as significant, a diversity of 0.92 was obtained. Isolates collected from fish showed lower diversity (Di = 0 .89) than those collected from other sources (environment, rotifers, A rtemia) (Di = 0.98). The lowest diversities were found among isolates collected from rainbow trout (Oncorhynchus mykiss), salmon (Salmo sola r) and turbot (Scophthalmus maximus). Isolates from close geographical locations were also less diverse than isolates obtained from more dis tant locations. We conclude that the diversity of V. anguillarum is hi gh, as shown by the combined typing methods. However, it seems that st rains with specific characteristics are associated with certain geogra phic areas, and also with certain fish species. This could only be det ected by applying a combination of several typing methods. Our results emphasise the need to use several different typing methods for studie s of bacterial diversity.