Department of Food Science, Cornell University, Ithaca, New York, USA
Department of Plant Sciences, University of California, Davis, California, USA.
Appl Environ Microbiol. 2020 Aug 18;86(17). doi: 10.1128/AEM.00899-20.
The Food Safety Modernization Act (FSMA) includes a time-to-harvest interval following the application of noncompliant water to preharvest produce to allow for microbial die-off. However, additional scientific evidence is needed to support this rule. This study aimed to determine the impact of weather on the die-off rate of and on spinach and lettuce under field conditions. Standardized, replicated field trials were conducted in California, New York, and Spain over 2 years. Baby spinach and lettuce were grown and inoculated with an ∼10-CFU/ml cocktail of and attenuated Leaf samples were collected at 7 time points (0 to 96 h) following inoculation; and were enumerated. The associations of die-off with study design factors (location, produce type, and bacteria) and weather were assessed using log-linear and biphasic segmented log-linear regression. A segmented log-linear model best fit die-off on inoculated leaves in most cases, with a greater variation in the segment 1 die-off rate across trials (-0.46 [95% confidence interval {95% CI}, -0.52, -0.41] to -6.99 [95% CI, -7.38, -6.59] log die-off/day) than in the segment 2 die-off rate (0.28 [95% CI, -0.20, 0.77] to -1.00 [95% CI, -1.16, -0.85] log die-off/day). A lower relative humidity was associated with a faster segment 1 die-off and an earlier breakpoint (the time when segment 1 die-off rate switches to the segment 2 rate). Relative humidity was also found to be associated with whether die-off would comply with FSMA's specified die-off rate of -0.5 log die-off/day. The log-linear die-off rate proposed by FSMA is not always appropriate, as the die-off rates of foodborne bacterial pathogens and specified agricultural water quality indicator organisms appear to commonly follow a biphasic pattern with an initial rapid decline followed by a period of tailing. While we observed substantial variation in the net culturable population levels of and at each time point, die-off rate and FSMA compliance (i.e., at least a 2 log die-off over 4 days) appear to be impacted by produce type, bacteria, and weather; die-off on lettuce tended to be faster than that on spinach, die-off of tended to be faster than that of attenuated , and die-off tended to become faster as relative humidity decreased. Thus, the use of a single die-off rate for estimating time-to-harvest intervals across different weather conditions, produce types, and bacteria should be revised.
《食品安全现代化法案》（FSMA）包含了在不遵守规定的水应用于收获前农产品后，进行收获前的时间间隔，以允许微生物死亡。然而，需要更多的科学证据来支持这一规定。本研究旨在确定天气对菠菜和生菜中 和 的死亡速度的影响，这些细菌是在田间条件下产生的。在加利福尼亚州、纽约州和西班牙进行了为期 2 年的标准化、重复田间试验。婴儿菠菜和生菜被种植并接种了约 10-CFU/ml 的 和衰减 的鸡尾酒。接种后 7 个时间点（0 至 96 小时）采集叶样本；并对 和 进行了计数。使用对数线性和双相分段对数线性回归评估了死亡与研究设计因素（地点、产品类型和细菌）和天气的关系。在大多数情况下，分段对数线性模型最适合接种叶片的死亡情况，试验中第一段死亡速率的变化较大（-0.46[95%置信区间{95%CI}，-0.52，-0.41]至-6.99[95%CI，-7.38，-6.59]log 死亡/天），而第二段死亡速率的变化较小（0.28[95%CI，-0.20，0.77]至-1.00[95%CI，-1.16，-0.85]log 死亡/天）。相对湿度较低与第一段死亡速度较快和较早的断点（第一段死亡速度切换到第二段速度的时间）有关。还发现相对湿度与死亡是否符合 FSMA 规定的-0.5 log 死亡/天的死亡速度有关。FSMA 提出的对数线性死亡速度并不总是合适的，因为食源性细菌病原体和规定的农业水质指示生物的死亡速度似乎通常遵循双相模式，初始快速下降，然后是一段滞后期。虽然我们在每个时间点都观察到 和 的可培养总种群水平有很大的差异，但死亡速度和 FSMA 的合规性（即，在 4 天内至少减少 2 个对数）似乎受到产品类型、细菌和天气的影响；生菜的死亡速度比菠菜快，衰减 的死亡速度比 的快，随着相对湿度的降低，死亡速度趋于加快。因此，应该修改在不同天气条件、产品类型和细菌下估计收获前时间间隔的单一死亡速度。
