Schmitz-Esser Stephan, Müller Anneliese, Stessl Beatrix, Wagner Martin
Department for Farm Animals and Veterinary Public Health, Institute for Milk Hygiene, University of Veterinary Medicine Vienna Vienna, Austria.
Front Microbiol. 2015 Apr 28;6:380. doi: 10.3389/fmicb.2015.00380. eCollection 2015.
The food-borne pathogen Listeria (L.) monocytogenes is often found in food production environments. Thus, controlling the occurrence of L. monocytogenes in food production is a great challenge for food safety. Among a great diversity of L. monocytogenes strains from food production, particularly strains belonging to sequence type (ST)121 are prevalent. The molecular reasons for the abundance of ST121 strains are however currently unknown. We therefore determined the genome sequences of three L. monocytogenes ST121 strains: 6179 and 4423, which persisted for up to 8 years in food production plants in Ireland and Austria, and of the strain 3253 and compared them with available L. monocytogenes ST121 genomes. Our results show that the ST121 genomes are highly similar to each other and show a tremendously high degree of conservation among some of their prophages and particularly among their plasmids. This remarkably high level of conservation among prophages and plasmids suggests that strong selective pressure is acting on them. We thus hypothesize that plasmids and prophages are providing important adaptations for survival in food production environments. In addition, the ST121 genomes share common adaptations which might be related to their persistence in food production environments such as the presence of Tn6188, a transposon responsible for increased tolerance against quaternary ammonium compounds, a yet undescribed insertion harboring recombination hotspot (RHS) repeat proteins, which are most likely involved in competition against other bacteria, and presence of homologs of the L. innocua genes lin0464 and lin0465.
食源性病原体单核细胞增生李斯特菌（Listeria (L.) monocytogenes）在食品生产环境中经常被发现。因此，控制食品生产中单核细胞增生李斯特菌的出现对食品安全来说是一项巨大挑战。在来自食品生产的多种多样的单核细胞增生李斯特菌菌株中，特别是属于序列型（ST）121的菌株很普遍。然而，目前尚不清楚ST121菌株大量存在的分子原因。因此，我们测定了三株单核细胞增生李斯特菌ST121菌株的基因组序列：6179和4423，它们在爱尔兰和奥地利的食品生产工厂中持续存在了长达8年，以及菌株3253，并将它们与现有的单核细胞增生李斯特菌ST121基因组进行了比较。我们的结果表明，ST121基因组彼此高度相似，并且在它们的一些前噬菌体中，特别是在它们的质粒中显示出极高的保守程度。前噬菌体和质粒之间这种非常高的保守水平表明有强大的选择压力作用于它们。因此，我们推测质粒和前噬菌体为在食品生产环境中的生存提供了重要的适应性。此外，ST121基因组具有共同的适应性，这可能与它们在食品生产环境中的持久性有关，例如存在Tn6188，一种负责提高对季铵化合物耐受性的转座子，一个尚未描述的含有重组热点（RHS）重复蛋白的插入片段，这些蛋白很可能参与与其他细菌的竞争，以及无害李斯特菌基因lin0464和lin0465的同源物的存在。
