Machado Henrique, Lourenço António, Carvalho Filipe, Cabanes Didier, Kallipolitis Birgitte H, Brito Luísa
CBAA/DRAT, Laboratório de Microbiologia, Instituto Superior de Agronomia, Technical University of Lisbon, Lisbon, Portugal.
J Mol Microbiol Biotechnol. 2013;23(3):209-18. doi: 10.1159/000348245. Epub 2013 Apr 16.
Listeria monocytogenes, a foodborne pathogenic bacterium, remains a serious public health concern due to its frequent occurrence in food products coupled with a high mortality rate. Bacterial pathogenicity depends greatly on the ability to secrete virulence factors to or beyond the bacterial cell surface. The Tat pathway, one of the secretion systems present in L. monocytogenes, was until now only investigated in silico. In L. monocytogenes strain EGDe two genes constitute this pathway, tatC(lmo0361) and tatA(lmo0362). Here we show that tatC and tatA are cotranscribed in a bicistronic- and growth-phase-dependent manner, being downregulated in the stationary phase. An EGDe tatAC mutant strain (EGDe ΔtatAC) was constructed, confirming that the Tat pathway is not essential for L.monocytogenes survival or biofilm-forming ability. When compared to the wild-type EGDe, deletion of tatAC did not decrease the virulence potential of EGDe ΔtatAC in HT-29 human epithelial cell line and even increased (p < 0.05) the virulence potential for mice. Moreover, we show that tat genes are prevalent in L. monocytogenes strains belonging to genetic lineage II and are generally absent from lineage I, which is more associated with human cases, thus excluding the possibility of using the Tat system as a target for novel antimicrobial compounds targeting L.monocytogenes.
单核细胞增生李斯特菌是一种食源性致病细菌，由于其在食品中频繁出现且死亡率高，仍然是一个严重的公共卫生问题。细菌致病性在很大程度上取决于分泌毒力因子至细菌细胞表面或其之外的能力。Tat途径是单核细胞增生李斯特菌中存在的分泌系统之一，到目前为止仅在计算机模拟中进行了研究。在单核细胞增生李斯特菌EGDe菌株中，两个基因构成了该途径，即tatC（lmo0361）和tatA（lmo0362）。在这里我们表明，tatC和tatA以双顺反子和生长阶段依赖性方式共转录，在稳定期被下调。构建了一个EGDe tatAC突变株（EGDe ΔtatAC），证实Tat途径对于单核细胞增生李斯特菌的存活或生物膜形成能力不是必需的。与野生型EGDe相比，tatAC的缺失并没有降低EGDe ΔtatAC在HT-29人上皮细胞系中的毒力潜力，甚至增加了（p < 0.05）对小鼠的毒力潜力。此外，我们表明tat基因在属于遗传谱系II的单核细胞增生李斯特菌菌株中普遍存在，而在与人类病例更相关的谱系I中通常不存在，因此排除了将Tat系统用作针对单核细胞增生李斯特菌的新型抗菌化合物靶点的可能性。
