Dept. of Food Science and Technology, Univ. of Georgia, 1109 Experiment St., Griffin, GA, 30223-1797, U.S.A.
J Food Sci. 2018 Jul;83(7):1913-1920. doi: 10.1111/1750-3841.14203. Epub 2018 Jun 15.
The use of electrolyzed oxidizing (EO) water to inactivate microorganisms on foods has been extensively studied and shown to be effective. However, the prospect of the formation of "viable but nonculturable" (VBNC) cells in pathogens after low free chlorine concentration (FCC) treatments under high organic loads presents safety concerns. This study investigated the effect of EO water FCC on inducing Escherichia coli O157:H7 and Listeria monocytogenes into the VBNC state and studied possible resuscitation triggering procedures of the VBNC cells. A 5-strain cocktail of each pathogen (10 colony forming units [CFU]/mL) was exposed to EO water (FCC of 20, 10, 5, 2.5, 1.25, 0.625 mg/L) and allowed to stand for 1 and 5 min, followed by the addition of neutralizing broth. Treated samples were plated on nonselective agar and analyzed using flow cytometry. For resuscitation, samples treated with identified VBNC induction conditions were exposed to elevated temperatures (37 °C) as well as addition of sodium pyruvate (SP) and Tween® 20 (T20) solutions. The initial culturing procedures suggested complete inactivation of both pathogens at 2.5 and 1.25 mg/L FCC in the growth medium. However, flow cytometry profiles showed VBNC cells were present. Subjecting samples to the recovery procedures further proved that VBNC E. coli O157:H7 can be resuscitated after exposure to SP and T20 at 37 °C, while L. monocytogenes did not resuscitate. These findings show that treating pathogens at low FCC can induce the VBNC state, and culturability of E. coli O157:H7 can be restored under appropriate conditions.
VBNC induction conditions for foodborne pathogens during chlorine washing treatment were determined in a broth system and the information can serve as a basis for future studies that address the prevention of VBNC formation during produce wash treatments.
使用电解氧化（EO）水来灭活食品上的微生物已被广泛研究，并已证明其有效。然而，在高有机负荷下，低游离氯浓度（FCC）处理后病原体形成“存活但非可培养”（VBNC）细胞的前景引起了安全问题。本研究调查了 EO 水 FCC 对诱导大肠杆菌 O157：H7 和单核细胞增生李斯特菌进入 VBNC 状态的影响，并研究了 VBNC 细胞可能的复苏触发程序。将每种病原体的 5 株混合（10 个菌落形成单位 [CFU]/mL）暴露于 EO 水（FCC 为 20、10、5、2.5、1.25、0.625 mg/L）并静置 1 和 5 分钟，然后加入中和肉汤。处理后的样品在非选择性琼脂上平板，并使用流式细胞术进行分析。对于复苏，用鉴定的 VBNC 诱导条件处理的样品暴露于高温（37°C）以及添加丙酮酸钠（SP）和吐温® 20（T20）溶液。初始培养程序表明，在生长培养基中，2.5 和 1.25 mg/L FCC 下可完全灭活两种病原体。然而，流式细胞术图谱显示存在 VBNC 细胞。将样品置于恢复程序中进一步证明，暴露于 37°C 下的 SP 和 T20 后，VBNC 大肠杆菌 O157：H7 可以复苏，而单核细胞增生李斯特菌则不能复苏。这些发现表明，在低 FCC 下处理病原体可诱导 VBNC 状态，并且在适当条件下，大肠杆菌 O157：H7 的可培养性可以恢复。
在基于肉汤的系统中确定了食源性病原体在氯洗涤处理过程中 VBNC 诱导条件，这些信息可以为未来的研究提供依据，这些研究旨在解决在农产品清洗处理过程中防止 VBNC 形成的问题。
