AN ANALYSIS OF THE EXTRACELLULAR GROWTH PRODUCTS OF AEROMONAS SALMONICIDA AS VIRULENCE FACTORS AND POTENTIAL IMMUNOGENS
Because certain pathological changes in fish with furunculosis have been associated with the extracellular factors produced by Aeromonas salmonicida, the extracellular growth products of this bacterium were studied for their relation to bacterial virulence and their potential as immunogens against furunculosis. The extracellular growth products were extracted from culture supernatants of A. salmonicida by a combination of amonium sulfate and ethanol precipitations. Crude extracellular product material was then fractionated into four component protein groups (EcF I-IV) by ion exchange chromatography. The EcF-II produced in these studies was indicated to be the leukocytolytic factor produced by this bacterium. The relationship of A. salmonicida leukocytolytic properties to the virulence of study isolates was determined by direct bacterial cell leukocytolytic assays, production of the EcF-II by each isolate, and the specific activity of the EcF-II from each isolate on brook trout leukocytes. The isolates used in these assays were ranked under each of these categories in order of descending activity and, as a result, a positive correlation between the leukocytolytic properties and virulence of A. salmonicida isolates were not observed. However, intramuscular injection of the EcF-II from a virulent isolate produced hemorrhaging and mortality among juvenile brook trout and this component was also toxic to cultured RTG-2 cells. For these reasons the EcF-II was determined to be a generalized cytotoxin. The weak neutralization of this component by immune trout sera also indicated it to be a principal virulence antigen of A. salmonicida.^ EcF-I and EcF-III were also determined to be virulence factors of this bacterium based upon the in vivo response of brook trout to injection of these components and their reactivities in both RTG-2 cytotoxicity assays and serum neutralization assays.^ The serum neutralization assays developed in this study also provided a method for the detection of differences in the antigens produced by a virulent and an avirulent isolate of A. salmonicida. Major differences were reported in the response of either immune sera or normal trout serum to the EcF-III and EcF-IV produced by a virulent and an avirulent isolate of A. salmonicida. The response of normal trout serum in the assays with EcF-III and EcF-IV from an avirulent isolate not only indicated why this isolate was avirulent but suggested these two components to be potential immunogens.^ After the development of a reliable challenge system for the production of furunculosis in experimental fish, protection studies were initiated with EcF-II in juvenile brook trout. These results indicated that EcF-II is a protective antigen for the immunization of fish against furunculosis. ^
CIPRIANO, ROCCO CARMINE, "AN ANALYSIS OF THE EXTRACELLULAR GROWTH PRODUCTS OF AEROMONAS SALMONICIDA AS VIRULENCE FACTORS AND POTENTIAL IMMUNOGENS" (1980). ETD Collection for Fordham University. AAI8020054.