The Effect of Heat Shock on the Response ofCronobacter sakazakiito Subsequent Lethal Stresses

Abstract

Cronobacter sakazakii, formerly Enterobacter sakazakii, has been implicated in a severe form of neonatal meningitis. In this study, C. sakazakii BCRC 13988 was first exposed to heat-shock treatment at 47 degrees C for 15 min. The heat-shocked C. sakazakii was subjected to several lethal challenges including low temperature (3 degrees C and -20 degrees C), pH 3.3, 15% ethanol, high osmotic pressure (tryptic soy broth + 75% sorbitol, a(w) 0.81), and drying. It was found that heat shock significantly (p < 0.05) enhanced the resistance of C. sakazakii to all the lethal stresses examined. After 60 min of exposure to 15% ethanol, the survival of the heat-shocked cells was approximately 752 times that of the nonshocked cells. Compared with the nonshocked C. sakazakii, the heat-shocked cells exhibited a 322- and 1.6-fold increase in survival after 7 days of exposure to -20 degrees C and 3 degrees C, respectively. A 48-fold increase in the survival was noted with the heat-shocked cells after 6 h of exposure to dry air (relative humidity 37%) at 25 degrees C, showing a survival of 0.00107% which is approximately 50-fold that of the control. After 36 h of exposure to the high osmotic stress environment, the survival of the heat-shocked C. sakazakii was found to be approximately 119 times that of the control cells. Finally, an increased survival of approximately 72 times that of the control cells was observed with the heat-shocked C. sakazakii after 60 min of challenge at pH 3.3.