TWENTY-THIRD ANNUAL EASTERN FISH HEALTH WORKSHOP JOHN CARVER INN, PLYMOUTH, MA 30 MARCH - 2 APRIL, 1998 Atypical Aeromonas salmonicida: Aa Biological Conundrum Brian Austin Department of Biological Sciences, Heriot-Watt University, Riccarton, Edinburgh EH14 4AS, Scotland (U.K.) The literature abounds with references to atypical Aermonas salmonicida. Yet, it is often unclear why isolates should be regarded as "atypical". A consensus view would include oxidase-negativity, nutritional fastidiousness, and the lack of- or slow- pigment production. Whatever the definition, atypical A. salmonicida appear to be increasing in significance in cyprinids, native marine (flat)fish and salmonids. Yet, as a result of an examination of 52 isolates recovered from a wide range of hosts and geographical locations, it was apparent that there was marked heterogeneity, particularly in terms of molecular and phenotypic characteristics. The outcome was that isolates could not be accommodated by the current classification of four subspecies (achromogenes, masoucida, salmonicida and smithia). There was incongruence between the molecular (PCR, RAPD and ribotyping) and phenotypic methods in terms of cluster membership. By PCR, 6 groups were described of which Group 1 encompassed 12 isolates including the type strain of A. salmonicida subsp. smithia. Group 2 accommodated 23 isolates including the reference cultures of subspecies achromogenes and masoucida. The named culture of Haemophilus piscium was recovered in Group 6. By ribotyping and RAPD, the reference cultures were recovered in separate groups. All methods pointed to the uniqueness of subspecies smithia. Most isolates contained 2-6 plasmids, of 2.3 to 150 kb in length. Nevertheless, all isolates possessed certain key characteristics, including Gram-negativity, and the absence of motility. Isolates were pathogenic to a range of species, including Atlantic salmon, goldfish, rainbow trout and turbot. Control was possible by use of existing furunculosis vaccines, particularly those based on bacterial cells grown in conditions of iron-depletion and administered by intraperitoneal injection, by some chemotherapeutants, e.g. oxytetracycline, and by use of probiotics, notably Carnobacterium and Vibrio alginolyticus.   Return to 23rd Annual Eastern Fish Health Workshop Return to Leetown Science Center Home Page