次致死乙醇處理影響Cronobacter sakazakii之細胞膜脂肪酸組成及其在後續致死環境下之存活

Abstract

本研究探討 Cronobacter sakazakii以次致死乙醇處理後於後續壓力環境高濃度乙醇 (15%)、高溫 (51℃)、低溫 (4及-20℃)、低水活性 (Tryptic soy broth + 75% sorbitol, Aw= 0.83)、酸性 (pH 3.3)和有機酸(乳酸、醋酸、丙酸、酒石酸及檸檬酸)環境下，以及不同乾燥製程(噴霧乾燥及冷凍乾燥)下存活之情形。並進一步探討次致死乙醇處理之菌體細胞膜脂肪酸組成之變化。結果發現以5%乙醇濃度處理60分鐘最顯著提升C. sakazakii BCRC 13988於後續15%乙醇濃度環境下之存活，此處理亦顯著提升了其於後續壓力下之耐受性。次致死乙醇濃度處理也顯著提升了菌體在模擬噴霧乾燥製程之存活率，然而於模擬冷凍乾燥製程中其存活率則無顯著差異。此外，以氣相層析質譜儀觀測菌體脂肪酸組成變化，發現C. sakazakii經次致死乙醇處理後其飽和脂肪酸與不飽和脂肪酸含量的比值顯著上升(p ＜0.05)，並且其細胞膜中cyclopropaneoctanoic acid比例也呈現顯著上升(p ＜0.05)的情形，這種改變可能會造成細胞膜流動性減低而使得菌體得以調適低濃度乙醇壓力。

In the present study, Cronobacter sakazakii was exposed to a sub-lethal dose of 5% ethanol for 60 min at room temperatue (ethanol shock). The effect of ethanol shock on the survival of C. sakazakii subjected to subsequent adverse conditions including high ethanol concentration (15%), high temperature (51℃), low temperature (4 and -20 ℃), acid (pH 3.3), high osmotic pressure (Tryptic soy broth + 75% sorbitol, Aw= 0.83) , air drying as well as in the presence of various organic acid (125 mM lactic acid, acetic acid, propionic acid, citric acid and tartaric acid) was investigated. Besides fatty acid profile of the cells of ethanol-shocked C. sakazakii were compared with those of the non-shocked cells. Results revealed that ethanol shock cells significantly (P<0.05) enhanced the resistance of C. sakazakii to all the lethal stresses examined. Although survival of ethanol-shocked and non-shocked cells showed no significantly difference (P>0.05) after freeze-drying, survival of the ethanol-chocked C. sakazakii was significantly higher (P<0.05) than that of non-shocked cells after spray-drying. Furthermore, ethanol shock caused a change in the proportions of the saturated and unsaturated fatty acids. The ratio of saturated to unsaturated fatty acid and the proportion of cyclopropaneoctanoic acid in the ethanol-shocked cells was significantly higher (P<0.05) than that observed in the non-shocked cells.