Department of Food Science, Cornell University, 354 Stocking Hall, Ithaca, New York 14853, USA (ORCID: https://orcid.org/0000-0002-9143-508X [A.S.H.]; https://orcid.org/0000-0002-9523-0081 [L.K.S.]; https://orcid.org/0000-0002-4168-5662 [M.W.]; https://orcid.org/0000-0001-7259-6331 [D.W.]).
Department of Food Science and Technology, Eastern Shore Agriculture Research and Extension Center, Virginia Polytechnic Institute and State University, 33446 Research Drive, Painter, Virginia 23420, USA.
J Food Prot. 2020 Nov 1;83(11):1958-1966. doi: 10.4315/JFP-20-120.
Past studies have shown that the on-farm distribution of Listeria monocytogenes is affected by environmental factors (e.g., weather). However, most studies were conducted at large scales (e.g., across farms), whereas few studies examined drivers of L. monocytogenes prevalence at smaller scales (e.g., within a single field). This study was performed to address this knowledge gap by (i) tracking L. monocytogenes distribution in two fields on one farm over a growing season and (ii) identifying factors associated with L. monocytogenes isolation from drag swab, soil, and agricultural water samples. Overall, L. monocytogenes was detected in 78% (21 of 27), 19% (7 of 36), and 8% (37 of 486) of water, drag swab, and soil samples, respectively. All isolates were characterized by pulsed-field gel electrophoresis. Of the 43 types identified, 14 were isolated on multiple sampling visits and/or from multiple sample types, indicating persistence in or repeated introduction into the farm environment during the study. Our findings also suggest that L. monocytogenes prevalence, even at the small spatial scale studied here, (i) was not uniform and (ii) varied more within fields than between fields or over time. This is illustrated by plot (in-field variation), field (between-field variation), and sampling visit (time), accounting for 18, 2, and 3% of variance in odds of isolating L. monocytogenes, respectively. Moreover, according to random forest analysis, water-related factors were among the top-ranked factors associated with L. monocytogenes isolation from all sample types. For example, the likelihood of isolating L. monocytogenes from drag and soil samples increased monotonically as rainfall increased. Overall, findings from this single-farm study suggests that mitigation strategies for L. monocytogenes in produce fields should focus on water-associated risk factors (e.g., rain and distance to water) and be tailored to specific high-risk in-field areas.
过去的研究表明，单核细胞增生李斯特菌在农场的分布受环境因素（如天气）的影响。然而，大多数研究都是在较大规模上进行的（例如，跨农场），而很少有研究在较小规模上（例如，在单个田地内）研究单核细胞增生李斯特菌流行的驱动因素。本研究旨在通过（i）在一个生长季节内在一个农场的两个田地上追踪单核细胞增生李斯特菌的分布，以及（ii）确定与从拖拉拭子、土壤和农业用水样本中分离出单核细胞增生李斯特菌相关的因素，来填补这一知识空白。总体而言，在水、拖拉拭子和土壤样本中分别检测到 78%（21/27）、19%（7/36）和 8%（37/486）的单核细胞增生李斯特菌。所有分离株均通过脉冲场凝胶电泳进行了特征描述。在所鉴定的 43 种类型中，有 14 种在多次采样访问和/或从多种样本类型中分离出来，表明在研究期间，该菌在农场环境中持续存在或反复引入。我们的研究结果还表明，即使在本研究的小空间尺度上，单核细胞增生李斯特菌的流行率（i）并不均匀，（ii）在田间的变化大于田间之间或随时间的变化。这一点通过地块（田间内的变化）、田地（田间之间的变化）和采样访问（时间）来体现，分别占分离出单核细胞增生李斯特菌的几率的 18%、2%和 3%。此外，根据随机森林分析，与水相关的因素是与从所有样本类型中分离出单核细胞增生李斯特菌相关的排名最高的因素之一。例如，随着降雨量的增加，从拖拉拭子和土壤样本中分离出单核细胞增生李斯特菌的可能性呈单调递增。总的来说，这项单农场研究的结果表明，在农产品田地中减少单核细胞增生李斯特菌的策略应侧重于与水相关的风险因素（例如，降雨和与水的距离），并针对特定的高风险田间区域进行调整。
