Survival of Vibrio vulnificus under pH, salinity and temperature combined stress

The combined effect of low pH (5.0), low salinity (0.5%) and temperature (5 and 20 degrees C) on the survival of Vibrio vulnificus cells was studied. The effect of the combined stress was examined on the basis of the decrease in cell counts throughout 6 h of incubation in brain-heart infusion broth pH 5. Combined stress had an immediate effect that did not produce cellular lysis but a marked loss of culturability on thiosulphate citrate-bile salts-sucrose agar. However, a large number of cells remained viable, as determined both by direct viable counts and by colony forming units on non-selective medium. Cell injury affected a great number of cells but the survival fraction of non-injured cells remained above 20% of the initial number. The inactivation of a significant number of cells was examined in terms of the D-10-values. They varied depending on the parameter examined but in general D-10 values were obtained more rapidly at 20 than at 5 degrees C. However, after 24 h of incubation, when no cells could be detected onto non-selective medium, viable cells were defected by direct viable counts, both at 5 and 20 degrees C. (C) 1996 Academic Press Limited