CBQF/Escola Superior de Biotecnologia, Universidade Católica Portuguesa, Porto, Portugal.
Appl Environ Microbiol. 2011 Apr;77(8):2701-15. doi: 10.1128/AEM.02553-10. Epub 2011 Mar 4.
The persistence of Listeria monocytogenes in food-associated environments represents a key factor in transmission of this pathogen. To identify persistent and transient strains associated with production of fermented meat sausages in northern Portugal, 1,723 L. monocytogenes isolates from raw material and finished products from 11 processors were initially characterized by random amplification of polymorphic DNA (RAPD), PCR-based molecular serotyping, and epidemic clone characterization, as well as cadmium, arsenic, and tetracycline resistance typing. Pulsed-field gel electrophoresis (PFGE) typing of 240 representative isolates provided evidence for persistence of L. monocytogenes for periods of time ranging from 10 to 32 months for all seven processors for which isolates from different production dates were available. Among 50 L. monocytogenes isolates that included one representative for each PFGE pattern obtained from a given sample, 12 isolates showed reduced invasion efficiency in Caco-2 cells, including 8 isolates with premature stop codons in inlA. Among 41 isolates representing sporadic and persistent PFGE types, 22 isolates represented lysogens. Neither strains with reduced invasion nor lysogens were overrepresented among persistent isolates. While the susceptibility of isolates to lysogenic phages also did not correlate with persistence, it appeared to be associated with molecular serotype. Our data show the following. (i) RAPD may not be suitable for analysis of large sets of L. monocytogenes isolates. (ii) While a large diversity of L. monocytogenes subtypes is found in Portuguese fermented meat sausages, persistence of L. monocytogenes in this food chain is common. (iii) Persistent L. monocytogenes strains are diverse and do not appear to be characterized by unique genetic or phenotypic characteristics.
单核细胞增生李斯特菌在与食物相关的环境中持续存在是该病原体传播的一个关键因素。为了确定与葡萄牙北部发酵肉香肠生产相关的持久性和瞬时菌株，对来自 11 个加工商的原材料和成品中的 1723 株单核细胞增生李斯特菌分离株进行了初始特征分析，包括随机扩增多态性 DNA（RAPD）、基于 PCR 的分子血清型分型、流行克隆特征以及镉、砷和四环素耐药性分型。240 个代表性分离株的脉冲场凝胶电泳（PFGE）分型为所有 7 个加工商提供了证据，这些加工商的分离株可追溯到不同的生产日期，表明单核细胞增生李斯特菌的持续存在时间从 10 个月到 32 个月不等。在包括从给定样本获得的每个 PFGE 模式的一个代表的 50 个单核细胞增生李斯特菌分离株中，有 12 个分离株在 Caco-2 细胞中的入侵效率降低，包括 8 个在 inlA 中存在提前终止密码子的分离株。在 41 个代表散发性和持久性 PFGE 型的分离株中，有 22 个代表溶原菌。在持久性分离株中，减少入侵的菌株和溶原菌均未过度表达。虽然分离株对溶原性噬菌体的敏感性与持久性也没有相关性，但似乎与分子血清型有关。我们的数据表明：（i）RAPD 可能不适合分析大量单核细胞增生李斯特菌分离株。（ii）虽然葡萄牙发酵肉香肠中发现了大量单核细胞增生李斯特菌亚型，但该食物链中单核细胞增生李斯特菌的持续存在很常见。（iii）持久性单核细胞增生李斯特菌菌株多样，似乎没有独特的遗传或表型特征。
