熱震處理阪崎腸桿菌在一些致死壓力下及乳酸發酵過程與產品貯存時之活性

Abstract

阪崎腸桿菌 (Cronobacter sakazakii) 為革蘭氏陰性菌，是一種新興食源性病原菌，常能存活於嬰兒配方奶粉等食品中，感染引發新生兒之腦膜炎、壞死性小腸結腸炎和菌血症等疾病，並具有40%~80% 之高致死率。本研究將C. sakazakii BCRC 13988進行47℃-15 min之熱震處理，探討其於一些後續致死環境壓力 (有機酸、模擬胃腸液、消毒劑) 及乳酸發酵過程與產品貯存時之存活情形。 結果顯示，熱震處理顯著地 (p < 0.05) 提高了C. sakazakii菌體暴露於含40 mM 之有機酸 (乳酸、醋酸、丙酸、檸檬酸及酒石酸) 之磷酸緩衝溶液 (pH 4.0 )，於模擬胃液 (pH 2.0、3.0、3.5、4.0) 中，以及含消毒劑 (氯化合物、四級銨) 致死壓力下之耐受性，然而在含0.5%及2.0% 之膽鹽溶液中熱震與未熱震菌體之敏感性並無顯著性 (p > 0.05) 差異。 將熱震與未熱震之C. sakazakii 與Streptococcus thermophilus或Lactobacillus bulgaricus 同時接種於脫脂乳並置於37℃下進行發酵，在發酵初期24小時，菌數皆可迅速增加至約108-109 CFU/mL，其後菌數皆呈下降之現象，發酵48小時熱震之C. sakazakii 之存活菌數高於未熱震處理者。C. sakazakii 接種於市售發酵乳製品中並置於5℃下，於48 小時貯存過程，其存活菌數隨時間之延長而減少，惟熱震之存活菌數亦呈現高於未熱震者。

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.