Horne S M, Kottom T J, Nolan L K, Young K D
Department of Microbiology and Immunology, School of Medicine, University of North Dakota, Grand Forks 58202-9037, USA.
Infect Immun. 1997 Feb;65(2):806-10. doi: 10.1128/iai.65.2.806-810.1997.
The fkpA gene of Salmonella typhimurium encodes a protein similar to the macrophage infectivity potentiator (Mip) proteins of Legionella pneumophila and Chlamydia trachomatis. Because Mip proteins enhance the ability of these intracellular pathogens to survive within macrophages and epithelial cells, we tested whether the product of the fkpA gene would have the same effect on the intracellular growth of a virulent strain of S. typhimurium. By a series of P22 transductions, the fkpA gene of S. typhimurium Copenhagen was replaced with the inactive fkpA1::omega-Cm gene from Escherichia coli, creating the mutant S. typhimurium KY32H1. The Copenhagen and KY32H1 strains were equally able to enter Caco-2 cells (an epithelial cell line) and J774.A1 cells (a macrophage-like cell line). However, compared to the parent, the fkpA mutant survived less well in both types of cells during the first 6 h after infection. The number of viable intracellular S. typhimurium Copenhagen bacteria remained constant 6 h after infection of Caco-2 cells, but the viability of S. typhimurium KY32H1 decreased significantly by 4 h postinfection. The fkpA mutant also exhibited a reduced ability to survive intracellularly in J774.A1 cells as little as 2 h postinfection. Complementation of the fkpA mutation by a plasmid-borne wild-type fkpA gene from E. coli restored the ability of S. typhimurium KY32H1 to grow normally in J774.A1 cells. Thus, expression of the mip-like fkpA gene confers on S. typhimurium Copenhagen properties analogous to those mediated by the Mip proteins in other intracellular pathogens, suggesting that this mechanism may play a role in the virulence and/or intracellular growth of numerous bacteria.
鼠伤寒沙门氏菌的fkpA基因编码一种蛋白质，该蛋白质与嗜肺军团菌和沙眼衣原体的巨噬细胞感染增强因子（Mip）蛋白相似。由于Mip蛋白可增强这些细胞内病原体在巨噬细胞和上皮细胞内存活的能力，因此我们测试了fkpA基因产物是否会对鼠伤寒沙门氏菌强毒株的细胞内生长产生同样的影响。通过一系列P22转导，将鼠伤寒沙门氏菌哥本哈根菌株的fkpA基因替换为来自大肠杆菌的无活性fkpA1::omega-Cm基因，从而构建出突变体鼠伤寒沙门氏菌KY32H1。哥本哈根菌株和KY32H1菌株进入Caco-2细胞（一种上皮细胞系）和J774.A1细胞（一种巨噬细胞样细胞系）的能力相同。然而，与亲本相比，fkpA突变体在感染后的最初6小时内在这两种细胞中的存活能力较差。感染Caco-2细胞6小时后，细胞内存活的鼠伤寒沙门氏菌哥本哈根菌株数量保持恒定，但感染后4小时，鼠伤寒沙门氏菌KY32H1的活力显著下降。fkpA突变体在感染J774.A1细胞后仅2小时，其在细胞内存活的能力也降低。用来自大肠杆菌的质粒携带的野生型fkpA基因对fkpA突变进行互补，可恢复鼠伤寒沙门氏菌KY32H1在J774.A1细胞中正常生长的能力。因此，类Mip的fkpA基因的表达赋予鼠伤寒沙门氏菌哥本哈根菌株与其他细胞内病原体中Mip蛋白介导的特性类似的特性，这表明该机制可能在众多细菌的毒力和/或细胞内生长中发挥作用。
