Host Response to Gene Knockouts in the Pyruvate Metabolism Pathway of Salmonella typhimurium

Salmonellosis remains one of the most widespread and prevalent foodborne diseases worldwide. Yet a complete understanding of the human-Salmonella interactome has thus far not been realized. Two Salmonella genes in the pyruvate metabolism pathway, pyruvate formate lyase I (ΔpflB) and acetaldehyde-CoA/alcohol dehydrogenase (ΔadhE), were significantly up-regulated in our previous host-Salmonella whole genome profiling study. Therefore, knockout mutants of these Salmonella genes were generated by the lambda red recombinase system to assess the effects of these genes on host infectivity. A time-course infection study was performed on cell line HCT-8, human intestinal epithelia, as well as a macrophage cell line THP-1. Host cell intracellular bacteria were counted at 1h, 4h, 18h, 24h, and 48h post-infection using the gentamicin protection assay. The results show that epithelial cells infected with either mutant strain had significantly (p<0.01) higher numbers of bacteria than the wild-type from 4h post-infection to 48h PI. Multiple Salmonella pathogenicity island-1 (SPI1) genes were up-regulated in the mutant strain, including 4 SPI1 genes tested from cultures alone and 7-13 SPI1 genes measured within invaded HCT-8 cells at any measured time post-infection. Then, host gene expression was profiled by a 4x44K human microarray using HCT-8 cells infected with either the wild-type (WT) or one of mutant (MT) strain (ΔpflB) normalized to control cells at 4h, 24h, and 48h post-infection. Differentially expressed genes were identified at FDR 20% and 2-fold cutoff. The gene ontology and pathway analysis are underway to understand cellular mechanisms of pflB effect on pathogenesis of Salmonella infection in humans.