Inhibitory effects of focA-positive and focA-negative E. coli isolates on Salmonella Typhimurium invasion.

Confluent monolayers of IPEC-J2 cells were pre-incubated with E. coli Nissle 1917 (EcN, focA-positive strain), E. coli WS15C1 (focA-positive strain), E. coli WS30C1 (focA-negative strain) and E. coli WS46C1 (focA-negative strain) using an MOI of 100∶1 E. coli to host cells. After two hours, cells were washed and adhesion efficiencies of E. coli isolates were determined (left side); alternatively, cells were washed after two hours and infected with Salmonella Typhimurium using an MOI of 100∶1 Salmonella to host cells (right side). Adhesion levels in percent (%) were expressed relative to adhesion of EcN. Invasion levels in percent (%) were expressed relative to Salmonella invasion without pre-incubation with bacteria (Salmonella mono-infection). The data are the mean ± S.E.M. of at least three separate experiments in duplicate wells. * = p<0.01 compared to EcN adhesion (left side) or Salmonella mono-infection (right side).