Coomassie Brilliant Blue Agar was used to quantify the frequency of the A-layer phenotype in different isolates of Aeromonas salmonicida. Hydrophilic, non-clumping isolates of A. salmonicida consisted predominantly of the A-layer minus phenotype. These bacteria were avirulent by intraperitoneal injection into susceptible brook trout (Salvelinus fontinalis) and could not be reisolated from infected fish. By contrast, hydrophobic, clumping isolates were predominantly of the A-layer positive phenotype, highly virulent in brook trout, and easily recovered from dead or moribund fish. A-layer positive and negative clones of A. salmonicida were derived by plating bacteria on Coomassie Blue Agar. The plating showed clearly that Coomassie Blue Agar could be used as a highly selective in vitro screening method to reclaim the virulence of certain isolates of A. salmonicida having a relatively low percentage of A-layer positive phenotypes.
Proteases with apparent molecular weights of 47, 40, 34 and 32 kD were identified in cellfree extracellular products (ECP) of Flexibacter colurnnaris by using substrate SDS-polyacrylamide gel electrophoresis. Similar protease profiles were associated with ECP collected at intervals during several days in culture. Furthermore, the proteases produced by a collection of 13 F. colurnnaris isolates from a variety of fish species and geographic sources showed great uniformity but differed markedly from the protease profiles of 7 other gliding bacteria examined. The 13 F. columnaris isolates degraded gelatin, casein, hemoglobin, fibrinogen and elastin. Results of experiments with protease inhibitors indicated that zinc metalloproteases constitute a major component of the extracellular proteases of F. columnarjs.
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