Department of Food Science, College of Agriculture and Life Sciences, Cornell Universitygrid.5386.8, Ithaca, New York, USA.
Department of Food Science and Technology, Eastern Shore Agricultural Research and Extension Center, Virginia Techgrid.438526.e, Painter, Virginia, USA.
Appl Environ Microbiol. 2022 Nov 22;88(22):e0117722. doi: 10.1128/aem.01177-22. Epub 2022 Oct 26.
The contamination of ready-to-eat produce with Listeria monocytogenes (LM) can often be traced back to environmental sources in processing facilities and packinghouses. To provide an improved understanding of sources and transmission in produce operations, we performed whole-genome sequencing (WGS) of LM ( = 169) and other spp. ( = 107) obtained from 13 produce packinghouses and three fresh-cut produce facilities. Overall, a low proportion of LM isolates (9/169) had premature stop codons, and a large proportion (83/169) had either or both of the LIPI-3 or LIPI-4 operons, which have been associated with hypervirulence. The further analysis of the WGS data by operation showed a reisolation (at least 2 months apart) of highly related isolates (<10 hqSNP differences) in 7/16 operations. Two operations had highly related strains reisolated from samples that were collected at least 1 year apart. The identification of isolates collected during preproduction (i.e., following sanitation but before the start of production) that were highly related to isolates collected during production (i.e., after people or products have entered and begun moving through the operation) provided evidence that some strains were able to survive standard sanitation practices. The identification of closely related isolates (<20 hqSNPs differences) in different operations suggests that cross-contamination between facilities or introductions from common suppliers may also contribute to transmission. Overall, our data suggest that the majority of LM isolates collected from produce operations are fully virulent and that both persistence and reintroduction may lead to the repeat isolation of closely related in produce operations. Listeria monocytogenes is of particular concern to the produce industry due to its frequent presence in natural environments as well as its ability to survive in packinghouses and fresh-cut processing facilities over time. The use of whole-genome sequencing, which provides high discriminatory power for the characterization of isolates, along with detailed source data (isolation date and sample location) shows that the presence of in produce operations appears to be due to random and continued reintroduction as well as to the persistence of highly related strains in both packinghouses and fresh-cut facilities. These findings indicate the importance of using high-resolution characterization approaches for root cause analyses of contamination issues. In cases of repeat isolation of closely related in a given facility, both persistence and reintroduction need to be considered as possible root causes.
单增李斯特菌（LM）污染即食农产品通常可追溯到加工设施和包装厂的环境源。为了更好地了解农产品操作中的来源和传播，我们对从 13 个农产品包装厂和 3 个新鲜切割农产品设施中获得的 LM（ = 169）和其他 spp.（ = 107）进行了全基因组测序（WGS）。总体而言，LM 分离株（9/169）中具有过早终止密码子的比例较低，而具有 LIPI-3 或 LIPI-4 操纵子的比例较大（83/169），这些操纵子与高致病性有关。通过操作进一步分析 WGS 数据显示，在 7/16 个操作中分离到至少 2 个月分离的高度相关分离株（<10 hqSNP 差异）。在至少相隔 1 年收集的样本中，两个操作分离到了高度相关的菌株。在生产前（即卫生处理后但生产开始前）收集的分离物与生产期间（即人员或产品进入并开始在操作中移动后）收集的分离物高度相关，这表明一些菌株能够存活标准的卫生处理。在不同操作中鉴定出高度相关的分离株（<20 hqSNP 差异）表明设施之间的交叉污染或来自共同供应商的引入也可能导致 传播。总体而言，我们的数据表明，从农产品操作中收集的大多数 LM 分离株都是完全有活力的，持久性和再引入都可能导致在农产品操作中重复分离出密切相关的 。单增李斯特菌由于其在自然环境中的频繁存在以及在包装厂和新鲜切割加工设施中随时间推移而存活的能力，对农产品行业特别关注。使用全基因组测序对 分离株进行高分辨力的特征描述，并结合详细的来源数据（分离日期和样本位置）表明，在农产品操作中存在 是由于随机且持续的再引入以及在包装厂和新鲜切割设施中高度相关菌株的持久性所致。这些发现表明，在对李斯特菌污染问题进行根本原因分析时，使用高分辨率的特征描述方法非常重要。在给定设施中重复分离出密切相关的 时，应考虑持久性和再引入作为可能的根本原因。
