Effect of Acid Adaptation on the Survival of Bacillus cereus under Subsequent Environmental Stresses and their Enterotoxin Production
|Keywords:||酸馴化處理;仙人掌桿菌;環境壓力;腸毒素;acid adaptation;Bacillus cereus;environmental stresses;enterotoxin||Issue Date:||2007||Abstract:||
本研究乃試圖了解酸馴化處理對仙人掌桿菌在後續環境壓力 (有機酸、高溫、低溫、高鹽、乙醇及過氧化氫) 下存活之情形，並探討酸馴化影響仙人掌桿菌腸毒素 (enterotoxin) 產生之情形。
結果顯示，在pH 5.5經過不同時間酸馴化處理之B. cereus 1-4-1，暴露於後續酸性環境 (pH 4.0) 4小時後，以酸馴化2小時處理之菌體有最高之存活率。當菌株暴露於含40 mM之有機酸 (醋酸、丙酸、乳酸、檸檬酸及酒石酸) 磷酸緩衝溶液 (pH 4.0) 時，酸馴化菌體對有機酸之耐受性較未酸馴化菌體高。此外，酸馴化處理可顯著 (p<0.05) 提升菌體對高溫 (49℃) 之耐受性及冷凍 (-18℃) 之抵抗力，然而酸馴化處理卻增加菌體對冷藏溫度 (4℃)、高塩 (20%) 及乙醇 (20%) 之敏感性，酸馴化菌體與未酸馴化對過氧化氫 (5 mM) 之敏感性並無顯著性 (p>0.05) 差異。酸馴化菌體所測得之菌體懸浮上清液及菌體分解液之腸毒素含量均較未酸馴化菌體低，當菌體生長於TSB培養基中，直到培養4小時前，酸馴化菌體之生長及腸毒素產量較未酸馴化菌體高。
This study was conducted to investigate the effect of acid adaptation on the survival of Bacillus cereus 1-4-1 under subsequent environmental stresses (organic acids, high and low temperatures, high salts, ethanol and hydrogen peroxide). Besides, the enterotoxin production and protein expression of B. cereus 1-4-1 as influenced by acid adaptation were also examined.
It was found that Bacillus cereus 1-4-1 cells subjected to acid adaptation at pH 5.5 for 2 h exhibited the highest percentage of survival after exposure to phosphate buffer solution with pH 4.0 for 4 h. The acid-adapted cells showed a higher tolerance than the non-adapted cells when exposure to phosphate buffer solution (pH 4.0) containing 40mM organic acids (acetic acid, propionic acid, lactic acid, citric acid, tartaric acid). Furthermore, acid adaptation significantly (p<0.05) increased the thermal tolerance (49℃) and freezing (-18℃) resistance of Bacillus cereus 1-4-1. On the other hand, acid adaptation increased the susceptibility of Bacillus cereus 1-4-1 to refrigerative temperature (4℃), high salts (20%) and ethanol (20%). It was also showed no significant difference (p>0.05) susceptibility of the acid-adapted cells and non-adapted cells to hydrogen peroxide (5 mM). The cell-free supernatant and cell lysate of the acid-adapted cells showed less amount of enterotoxin than that of the non-adapted cells. Grown in TSB, the acid-adapted cells exhibited a higher level of growth and enterotoxin production than did the non-adapted cells until after 4 h of cultivation.
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