Effect of ethanol shock pretreatment on the tolerance of Cronobacter sakazakii BCRC 13988 exposed to subsequent lethal stresses.

Cronobacter spp., formerly Enterobacter sakazakii, are human pathogens. They are the etiological agent of life-threating bacterial infections in infants. In this study, the survival behavior of C. sakazakii Bioresources Collection and Research Center (BCRC) 13988 in the presence of various ethanol concentrations was first examined. Besides, the test organism was subjected to treatment with 5% ethanol for 60 min (ethanol shock). The effect of ethanol shock on the resistance of C. sakazakii to lethal stresses, including high ethanol concentration (15%), low temperature (4°C and -20°C), high temperature (51°C) and high acidity (pH 3.3), was investigated. Results revealed that 4-5% ethanol is the maximum concentration that will allow C. sakazakii BCRC 13988 to grow in trypticase soy broth (TSB). Etthanol at 6% and 7% or more, respectively, exerted bacteriostatic and bactericidal effects, respectively, on the test organism. Although ethanol shock did not affect the resistance of C. sakazakii to a refrigerated temperature (4°C), the ethanol-shocked C. sakazakii survived better under other lethal stress conditions. After 50 min of exposure to 15% ethanol, the ethanol-shocked C. sakazakii showed a survival percentage of 16.11%, which was a 6400-fold increase over the control cells (<0.01%). On the other hand, the ethanol-shocked C. sakazakii exhibited a 45-fold higher survival after 120-min exposure to 51°C. At the end of the 7-day storage at -20°C, the ethanol-shocked cells exhibited a survival percentage of 0.25% which was significantly (p<0.05) higher than that (less than 0.01%) of the control. Additionally, the ethanol-shocked cells showed a survival percentage of 13.80% compared to only 1.60% noted with the control cells after exposure to pH 3.3 for 60 min.