SURVIVAL OF VIBRIO-VULNIFICUS UNDER PH, SALINITY AND TEMPERATURE COMBINED STRESS

The combined effect of low pH (5.0), low salinity (0.5%) and temperatu re (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-h eart 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 a nd by colony forming units on non-selective medium. Cell injury affect ed a great number of cells but the survival fraction of non-injured ce lls remained above 20% of the initial number. The inactivation of a si gnificant number of cells was examined in terms of the D-10-values. Th ey varied depending on the parameter examined but in general D-10 valu es were obtained more rapidly at 20 than at 5 degrees C. However, afte r 24 h of incubation, when no cells could be detected onto non-selecti ve medium, viable cells were defected by direct viable counts, both at 5 and 20 degrees C. (C) 1996 Academic Press Limited