Environmental Healthcare Unit, Centre for Biological Sciences, University of Southampton, Life Sciences Building, Highfield Campus, Southampton, SO17 1BJ, UK,
Microb Ecol. 2014 Apr;67(3):603-11. doi: 10.1007/s00248-013-0364-3. Epub 2014 Jan 23.
Listeria monocytogenes is a foodborne pathogen that can be transmitted through contaminated raw food or by ready-to-eat products that have been in contact with contaminated surfaces. Tap water (TW) is used to wash produce, as a processed food constituent and to wash processing surfaces and floors. The main aim of this work was to investigate the formation and survival of L. monocytogenes biofilms on stainless steel (SS) coupons in TW at 4, 22, 30 and 37 °C. For that, coupons with biofilm were visualised in situ while other coupons were scraped to quantify total cells by SYTO 9, cultivable numbers by plating onto brain heart infusion agar and viable numbers by the direct viable count method. Results showed that L. monocytogenes can form biofilms on SS surfaces in TW at any temperature, including at 4 °C. The number of total cells was similar for all the conditions tested while cultivable numbers varied between the level of detection (<8.3 CFU cm(-2)) and 3.5 × 10(5) CFU cm(-2), meaning between 7.0 × 10(4) and 1.1 × 10(7) cells cm(-2) have entered the viable but non-cultivable (VBNC) state. This work clearly demonstrates that L. monocytogenes can form biofilms in TW and that sessile cells can remain viable and cultivable in some conditions for at least the 48 h investigated. On the other hand, VBNC adaptation suggests that the pathogen can remain undetectable using traditional culture recovery techniques, which may give a false indication of processing surface hygiene status, leading to potential cross-contamination of food products.
李斯特菌是一种食源性病原体，可以通过受污染的生食或与受污染表面接触的即食产品传播。自来水（TW）用于清洗农产品、作为加工食品的成分以及清洗加工表面和地板。这项工作的主要目的是研究李斯特菌在 4、22、30 和 37°C 的 TW 中在不锈钢（SS）片上形成和存活生物膜。为此，通过 SYTO 9 对原位形成生物膜的片进行可视化，同时对其他片进行刮擦，以通过脑心浸液琼脂平板计数来量化总细胞数、通过平板计数来量化可培养细胞数，并通过直接活菌计数法来量化活菌数。结果表明，李斯特菌可以在 TW 中的 SS 表面上形成生物膜，包括在 4°C 时。所有测试条件下的总细胞数相似，而可培养细胞数在检测下限（<8.3 CFU cm(-2)) 和 3.5×10(5) CFU cm(-2) 之间变化，这意味着 7.0×10(4) 和 1.1×10(7) 个细胞 cm(-2) 已进入活但非可培养（VBNC）状态。这项工作清楚地表明，李斯特菌可以在 TW 中形成生物膜，并且在某些条件下，定殖细胞至少在 48 小时内仍能保持存活和可培养。另一方面，VBNC 适应表明，使用传统的培养回收技术可能无法检测到病原体，这可能会错误地表明加工表面卫生状况，导致食品产品的潜在交叉污染。
