The effect of temperature and length of heat shock treatment on the thermal tolerance and cell leakage of Cronobacter sakazakii BCRC 13988

Enterobacter sakazakii is an emerging opportunistic pathogen associated with life-threatening illnesses in infants, with infant formula serving as the principal mode of transmission. In the present study, C sakazakii (formely E. sakazakii) BCRC 13988 was subjected to various heat shock treatments (42-48 degrees C for 5-15 min). Its subsequent survival at 51 degrees C and the leakage of intracellular materials was investigated. It was found that 47 degrees C was the maximum growth temperature of the test organism. In addition, heat shock enhanced the thermal tolerance of C. sakazakii BCRC 13988. Within heat shock temperatures between 42 and 47 degrees C, the thermal tolerance enhancing effect increased as the length or temperature of the heat shock treatment was increased. However, increasing the heat shock temperature to 48 degrees C reduced the thermal tolerance enhancing effect. Among the various heat shocked cells examined. the 47 degrees C-15 min-heat shocked C. sakazakii exhibited the highest thermal tolerance. Moreover, electron micrograph analysis showed that heat shock treatment caused damage and disruption in C. sakazakii cells. There was a significant increase (P < 0.05) in the leakage of nucleic acid and protein in the supernatant of the heat shocked cell suspension that increased as the temperature and duration of heat shock increased. (C) 2009 Elsevier B.V. All rights reserved.