EXTRACELLULAR PROTEASE PRODUCTION BY DAIRY STRAINS OF AEROMONAS-HYDROPHILA AS AFFECTED BY GROWTH MEDIA AND INCUBATION-TEMPERATURE

The production of extracellular proteases by two strains of Aeromonas hydrophila of dairy origin was determined in two media at two differen t temperatures. With one exception (strain QV12 in skim milk agar), th e specific proteolytic activity (OD at 440 nm mg(-1) protein) of extra cellular products of each A. hydrophila strain was higher at 4 degrees C than at 28 degrees C. Also, the addition of skim milk to the cultur e medium increased the specific proteolytic activity of the extracellu lar products for each A. hydrophila strain at both temperatures (excep t strain QV12 at 4 degrees C). Ten electrophoretic bands showing prote olytic activity were detected, and none of these was similar to previo usly described proteases of A. hydrophila. The number of electrophoret ic bands showing protease activity was higher when strains were grown in skim milk agar than in brain heart infusion agar, with the temperat ure of incubation showing a minor effect on the types of proteases pro duced by the two A. hydrophila strains. These data suggest that the re gular presence of A. hydrophila in milk and dairy products may not be underestimated because milk could act as stimulant to the production ( by A. hydrophila strains of dairy origin) of extracellular proteases a ssociated with undesirable effects (spoilage, pathogenesis). (C) 1996 Academic Press Limited.