DECREASED INTRACELLULAR SURVIVAL OF AN FKPA MUTANT OF SALMONELLA-TYPHIMURIUM COPENHAGEN

The fkpA gene of Salmonella typhimurium encodes a protein similar to t he macrophage infectivity potentiator (Mip) proteins of Legionella pne umophila and Chlamydia trachomatis, Because Mip proteins enhance the a bility of these intracellular pathogens to survive within macrophages and epithelial cells, we tested whether the product of the fkpA gene w ould have the same effect on the intracellular growth of a virulent st rain of S. typhimurium. By a series of P22 transductions, the fkpA gen e of S. typhimurium Copenhagen was replaced with the inactive fkpA1::O mega-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 sur vived less well in both types of cells during the first 6 h after infe ction. The number of viable intracellular S. typhimurium Copenhagen ba cteria remained constant 6 h after infection of Caco-2 cells, but the viability of S. typhimurium KY32H1 decreased significantly by 4 h post infection. The fkpA mutant also exhibited a reduced ability to survive intracellularly in J774.A1 cells as little as 2 h postinfection. Comp lementation of the fkpA mutation by a plasmid borne wild-type fkpA gen e from E. coli restored the ability of S. typhimurium KY32H1 to grow n ormally in J774.A1 cells. Thus, expression of the mip-like fkpA gene c onfers on S. typhimurium Copenhagen properties analogous to those medi ated by the Mip proteins in other intracellular pathogens, suggesting that this mechanism may play a role in the virulence and/or intracellu lar growth of numerous bacteria.