National Food Institute, Technical University of Denmark, Kemitorvet, 2800 Kgs. Lyngby, Denmark.
Institute for Food Safety and Hygiene, Vetsuisse Faculty, University of Zürich, Switzerland.
Int J Food Microbiol. 2020 Sep 16;329:108662. doi: 10.1016/j.ijfoodmicro.2020.108662. Epub 2020 May 16.
Listeria monocytogenes is a foodborne pathogen whose biofilm formation and desiccation tolerance may contribute to its survival in the food industry. L. monocytogenes possesses three cold-shock domain family proteins (CspA, CspB and CspD) known to be essential for adaptation against various food-relevant stress conditions including cold growth. The role of Csps in desiccation tolerance and biofilm formation was investigated in csp mutants as well as twenty-one other wild-type (WT) strains. Mutants with a single (ΔcspA) or multiple (ΔcspAB, ΔcspAD and ΔcspABD) deletions of csp genes, in a desiccation sensitive WT background (L. monocytogenes EGD-e) were immotile and exhibited an elevated desiccation tolerance compared to the parent strain. However, deletion of cspA in the more desiccation resistant food and outbreak related L. monocytogenes strains 568 and 08-5578 had no impact on desiccation tolerance although compared to the parent strains the mutants were also immotile. A correlation between lower motility and higher desiccation tolerance was observed among the 20 WT strains (Spearman rank correlation, r = -0.56, p = 0.01), although exceptions occurred indicating that multiple factors influence the diverse desiccation tolerance among L. monocytogenes strains. Expression of cspA was upregulated in WT EGD-e, 568 and 08-5578 strains after desiccation for seven days, while the 568 and 08-5578 ΔcspA mutants expressed elevated levels of cspD and cspB (>30 fold higher) compared to their WTs. This indicates that upregulation of the other csps compensates for the deleted cspA gene. Although biofilm formation was improved in all EGDe csp mutants relative to the WT strain, the opposite was observed for 568 and 08-5578 WT strains and their cspA deletion mutants. Only motile strains formed biofilm in the peg lid assay but a significant negative correlation (r = -0.60, p = 0.01) was seen between higher motility and higher biofilm formation of WT strains. In conclusion, the survival of L. monocytogenes strains in the food processing environment may depend on the control of motility, which is a necessity for biofilm formation but disadvantageous for desiccation survival.
李斯特菌是一种食源性病原体，其生物膜形成和干燥耐受性可能有助于其在食品工业中的存活。李斯特菌具有三种冷休克结构域家族蛋白（CspA、CspB 和 CspD），已知这些蛋白对于适应各种与食品相关的应激条件（包括冷生长）至关重要。在干燥敏感的野生型（WT）背景下（李斯特菌 EGD-e），研究了 csp 突变体以及其他 21 种野生型菌株中 Csps 在干燥耐受性和生物膜形成中的作用。具有单个（ΔcspA）或多个（ΔcspAB、ΔcspAD 和 ΔcspABD）csp 基因缺失的突变体在运动方面不活跃，并且与亲本菌株相比表现出更高的干燥耐受性。然而，在更能抵抗干燥和与食物有关的李斯特菌菌株 568 和 08-5578 中，cspA 的缺失对干燥耐受性没有影响，尽管与亲本菌株相比，突变体也是不活跃的。在 20 种 WT 菌株中观察到较低的运动性和较高的干燥耐受性之间存在相关性（Spearman 等级相关，r = -0.56，p = 0.01），尽管存在例外情况，表明多种因素影响李斯特菌菌株之间不同的干燥耐受性。在 WT EGD-e、568 和 08-5578 菌株中，在干燥七天后，cspA 的表达上调，而 568 和 08-5578 ΔcspA 突变体与 WT 相比，cspD 和 cspB 的表达水平升高（高出 30 多倍）。这表明其他 Csps 的上调补偿了缺失的 cspA 基因。尽管与 WT 菌株相比，所有 EGDe csp 突变体的生物膜形成都得到了改善，但在 568 和 08-5578 WT 菌株及其 cspA 缺失突变体中观察到相反的情况。只有运动性菌株在 peg 盖测定中形成生物膜，但 WT 菌株和它们的 cspA 缺失突变体的高运动性与高生物膜形成之间存在显著的负相关（r = -0.60，p = 0.01）。总之，李斯特菌菌株在食品加工环境中的存活可能取决于运动性的控制，这是生物膜形成所必需的，但对干燥生存不利。
