FFoQSI GmbH-Austrian Competence Centre for Feed and Food Quality, Safety and Innovation, Technopark 1D, 3430 Tulln, Austria.
Unit of Food Microbiology, Institute for Food Safety, Food Technology and Veterinary Public Health, University of Veterinary Medicine Vienna, Veterinaerplatz 1, 1210 Vienna, Austria.
Int J Food Microbiol. 2024 Jan 30;410:110479. doi: 10.1016/j.ijfoodmicro.2023.110479. Epub 2023 Nov 9.
Listeria (L.) monocytogenes is of global concern for food safety as the listeriosis-causing pathogen is widely distributed in the food processing environments, where it can survive for a long time. Frozen vegetables contaminated with L. monocytogenes were recently identified as the source of two large listeriosis outbreaks in the EU and US. So far, only a few studies have investigated the occurrence and behavior of Listeria in frozen vegetables and the associated processing environment. This study investigates the occurrence of L. monocytogenes and other Listeria spp. in a frozen vegetable processing environment and in frozen vegetable products. Using whole genome sequencing (WGS), the distribution of sequence types (MLST-STs) and core genome sequence types (cgMLST-CT) of L. monocytogenes were assessed, and in-house clones were identified. Comparative genomic analyses and phenotypical characterization of the different MLST-STs and isolates were performed, including growth ability under low temperatures, as well as survival of freeze-thaw cycles. Listeria were widely disseminated in the processing environment and five in-house clones namely ST451-CT4117, ST20-CT3737, ST8-CT1349, ST8-CT6243, ST224-CT5623 were identified among L. monocytogenes isolates present in environmental swab samples. Subsequently, the identified in-house clones were also detected in product samples. Conveyor belts were a major source of contamination in the processing environment. A wide repertoire of stress resistance markers supported the colonization and survival of L. monocytogenes in the frozen vegetable processing facility. The presence of ArgB was significantly associated with in-house clones. Significant differences were also observed in the growth rate between different MLST-STs at low temperatures (4 °C and 10 °C), but not between in-house and non-in-house isolates. All isolates harbored major virulence genes such as full length InlA and InlB and LIPI-1, yet there were differences between MLST-STs in the genomic content. The results of this study demonstrate that WGS is a strong tool for tracing contamination sources and transmission routes, and for identifying in-house clones. Further research targeting the co-occurring microbiota and the presence of biofilms is needed to fully understand the mechanism of colonization and persistence in a food processing environment.
李斯特菌（L.） monocytogenes 是食品安全的全球性关注，因为这种引起李斯特菌病的病原体广泛分布于食品加工环境中，在那里它可以长时间存活。最近，受污染的冷冻蔬菜被确定为欧盟和美国两次大规模李斯特菌病爆发的源头。到目前为止，只有少数研究调查了冷冻蔬菜及其相关加工环境中李斯特菌的发生和行为。本研究调查了冷冻蔬菜加工环境和冷冻蔬菜产品中李斯特菌 monocytogenes 和其他李斯特菌的发生情况。使用全基因组测序（WGS），评估了李斯特菌 monocytogenes 的序列类型（MLST-ST）和核心基因组序列类型（cgMLST-CT）的分布，并鉴定了内部克隆。对不同 MLST-ST 和分离株进行了比较基因组分析和表型特征分析，包括低温下的生长能力以及耐冻融循环的能力。李斯特菌在加工环境中广泛传播，在环境拭子样本中存在的李斯特菌分离株中发现了五个内部克隆，即 ST451-CT4117、ST20-CT3737、ST8-CT1349、ST8-CT6243 和 ST224-CT5623。随后，在产品样本中也检测到了鉴定的内部克隆。输送带是加工环境中污染的主要来源。大量的应激抗性标记物支持李斯特菌在冷冻蔬菜加工设施中的定植和存活。ArgB 的存在与内部克隆显著相关。不同 MLST-ST 在低温（4°C 和 10°C）下的生长速率也存在显著差异，但内部和非内部分离株之间没有差异。所有分离株都携带主要的毒力基因，如全长 InlA 和 InlB 和 LIPI-1，但 MLST-ST 之间的基因组内容存在差异。本研究结果表明，WGS 是追踪污染来源和传播途径以及识别内部克隆的有力工具。需要进一步研究伴随的微生物群和生物膜的存在，以充分了解食品加工环境中定植和持续存在的机制。
