SulA-induced filamentation in Salmonella enterica serovar Typhimurium: effects on SPI-1 expression and epithelial infection

Aims: Salmonella enterica serovar Typhimurium is capable of adopting a filamentous phenotype in response to damage. How this adaptive response affects bacterial virulence is unclear. We have examined the hypothesis that filamentation affects the ability of Salmonella to infect host cells. Methods and Results: Expression of the cell division inhibitor SulA in Salm. Typhimurium SL1344 from an arabinose-inducible plasmid resulted in filamentation. We examined expression of the type 3 secretion system (T3SS) encoded by Salmonella pathogenicity island 1 (SPI-1) using SL1344 expressing a chromosomal PprgH-gfp reporter. Single cell analysis of SulA-induced SL1344 PprgH-gfp revealed a relationship between increasing cell length and decreasing propensity for prgH expression, but there was no evidence of a significant change in prgH expression evident at the whole population level. Filamentous Salm. Typhimurium were capable of initiating membrane ruffling on MDCK epithelial cells, but only nonfilamentous bacteria (