Acid resistance of Salmonella Typhimurium ATCC 14028 after desiccation stress during peanut storage

ABSTRACT: Salmonella is a relevant pathogen, which causes foodborne outbreaks associated with both high and low moisture foods (LMF). This study evaluated the effect of previous desiccation stress on the acid resistance of S. Typhimurium ATCC 14028 using blanched peanut kernels as an LMF model. Salmonella was recovered from the peanut samples throughout 180 days of blanched peanut kernels storage at 28 ºC. During this period two death rates were verified, 0.04 log cfu/g/day in the first 30 days and 0.007 log cfu/g/day between 30 and180 days.Regarding acid resistance, there was no difference (P > 0.05) in the Salmonella growth/death kinetics between the undesiccated sample (TSB)and the cells recovered from peanut samples over 180 days of storage after 4 h at pHs 3.0, 3.5, 4.5 and 7.2. The average growth rate observed for pH 7.2 was 0.44 log cfu/ml/h. At pH 4.5, the Salmonella counts did not change significantly over 4 h. In contrast, Salmonella populations declined by 0.14 to 0.29 log cfu/ml/h at pH 3.5. At pH 3.0 declines were estimated to be 0.65 log cfu/ml/h for the undesiccated sample and 2.07 log cfu/ml/h for Salmonella recovered from peanuts stored for 120 days. Therefore, our data indicated that desiccation stress caused during the peanut storagedid not influence the Salmonella acid resistance.

摘要：沙门氏菌是一类重要致病菌，可引发与高水分食品及低水分食品（LMF）相关的食源性暴发事件。本研究以烫漂去皮花生仁作为低水分食品（LMF）模型，探究预干燥胁迫对鼠伤寒沙门氏菌ATCC 14028耐酸性的影响。在28℃条件下储存烫漂去皮花生仁的180天周期内，本研究均从花生样本中分离得到沙门氏菌。此期间验证出两组死亡速率：前30天为0.04对数菌落形成单位/克/天，30至180天期间为0.007对数菌落形成单位/克/天。在耐酸性方面，经pH 3.0、3.5、4.5及7.2环境处理4小时后，未经过干燥胁迫的样本（胰蛋白胨大豆肉汤，TSB）与储存180天的花生样本中分离得到的菌体，其沙门氏菌生长/死亡动力学无统计学显著差异（P>0.05）。在pH 7.2条件下观测到的平均生长速率为0.44对数菌落形成单位/毫升/小时；在pH 4.5条件下，沙门氏菌菌落数在4小时内无显著变化。与之相反，在pH 3.5条件下，沙门氏菌种群以0.14至0.29对数菌落形成单位/毫升/小时的速率下降。在pH 3.0条件下，未经过干燥胁迫的样本的菌体数量下降速率估算为0.65对数菌落形成单位/毫升/小时，而从储存120天的花生样本中分离得到的沙门氏菌的下降速率则为2.07对数菌落形成单位/毫升/小时。综上，本研究数据表明，花生储存过程中施加的干燥胁迫并不会影响沙门氏菌的耐酸性。