Viability of Heat Shocked-Cronobacter sakazakii Subjected to Various Lethal Stresses and During the Fermentation as well as Storage of Lactic Cultured Milk
Date Issued
2009
Date
2009
Author(s)
Hsiao, Wan-Ling
Abstract
Cronobacter sakazakii is a Gram-negative, emerging opportunistic pathogen which has been associated with life-threatening cases in infants, with infant formulas been implicated as the mode of transmission, and with high mortality rate of 40-80%. In the present study, C. sakazakii BCRC13988, the type strain, was subjected to heat shock treatments (47℃, 15 min). Their subsequent survival to various stress conditions, including organic acid, simulated gastrointestinal and sanitizer. Besides, growth and survival behavior of heat-shocked C. sakazakii during the lactic fermentation of skim milk by Streptococcus thermophilus or Lactobacillus bulgaricus and during 48 h storage of commercial dairy lactic fermented products at 5 ℃ were also investigated. It was found that heat-shocked cells showed a higher tolerance than the non-heat-shocked cells when exposure to phosphate buffer solution (pH 4.0) containing 40 mM organic acid (lactic acid, acetic acid, propionic acid, citric acid, tartaric acid). Furthermore, heat shock treatment significantly (p < 0.05) increase the tolerance in simulated gastric acid (pH 2.0, 3.0, 3.5, 4.0) and sanitizer (chlorine and quaternary ammonia compound) in temperature and in 40℃. It was showed no significan difference (p > 0.05) susceptibility of heat-shocked cells and non-heat-shocked cells to bile solution (0.5%, 2.0%). During the lactic acid fermentation of skim milk, survival of heat-shocke cells of C. sakazakii was higher than the non-heat-shocked cells. Similar phenomenon was also noted during the storage of commercial lactic fermented product at 5℃. In addition, heat shock treatment may also enhance the tolerance of C. sakazakii to refrigerated temperature and other antimicrobial principles in fermented milk.
Subjects
heat shock
stresses
lactic fermentation
Type
thesis
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