Stress response of Aeromonas hydrophila following environmental challenges

Two strains of Aeromonas hydrophila were studied to determine the effects of four stresses: acid adaptation, acid shock starvation, and cold adaptation on subsequent heat tolerance (50degreesC) or freeze/thaw (-20degreesC/21degreesC) resistance. D-values (min or days) were calculated and interactions between stress and strain were evaluated. Survivor curves for heat tolerance and freeze/thaw resistance were nonlinear. Acid shock or acid adaptation effects on heat tolerance and freeze/thaw resistance were variable between the two strains (P<0.05). Starvation decreased heat tolerance (P<0.05) for both strains and had no effect on freeze/thaw resistance (P>0.05). Cold adaptation decreased heat tolerance for both strains and had no effect on freeze/thaw resistance. Both strains were more acid tolerant following prior exposure to acid stress (pH 5.0) in log phase (P<0.05). Log phase cells of strain ATCC 7965 were more acid tolerant than MSV1. No differences in acid tolerance were observed between strains of stationary phase cells. A. hydrophila does not appear to have a measurable phenotypic cross protective response to starvation or cold stress that enhances heat or freeze/thaw tolerance and has limited response to other stresses. (C) 2002 Elsevier Science Ltd. All rights reserved.