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（Salmonella）是一类重要的食源性病原菌，可引发与高低水分食品（LMF）相关的食源性暴发事件。本研究以烫漂去皮花生仁作为高低水分食品模型，探究了前期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，研究人员均从花生样本中分离得到了沙门氏菌。此期间观测到两个阶段的死亡速率：前30天为0.04 log 菌落形成单位（Colony Forming Unit，CFU）/g/天，30至180天则为0.007 log CFU/g/天。关于耐酸性，在pH 3.0、3.5、4.5和7.2的环境中孵育4小时后，未经过干燥胁迫的样本（胰蛋白胨大豆肉汤（Tryptic Soy Broth，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/死亡动力学无显著差异（P > 0.05）。pH 7.2条件下观测到的平均生长速率为0.44 log CFU/mL/h。在pH 4.5环境中，沙门氏菌菌量在4小时内无显著变化。与之相反，pH 3.5环境下沙门氏菌种群以0.14至0.29 log CFU/mL/h的速率下降。在pH 3.0环境中，未经过干燥胁迫的样本菌量下降速率约为0.65 log CFU/mL/h，而从储存120天的花生样本中分离得到的沙门氏菌下降速率则为2.07 log CFU/mL/h。综上，本研究数据表明，花生储存过程中产生的干燥胁迫并未对沙门氏菌的耐酸性产生影响。