Interactions of Salmonella enterica subspecies enterica serovar Typhimurium with gut bacteria

• Interactions between the human gut microbiota and S. Typhimurium were studied in batch cultures and a continuous colon model.
• The exponential growth of S. Typhimurium was halted in co-cultures with Escherichia coli.
• S. Typhimurium was inactivated by faecal bacteria in batch cultures.
• The growth of S. Typhimurium was inhibited by faecal bacteria in continuous cultures.

The aim of this study was to evaluate the impact of the gut microbiota on the growth and survival of S. Typhimurium. This was tested in two-species co-cultures and in mixed cultures with a simplified gut model microbiota. Subsequently, interactions between S. Typhimurium and human faecal bacteria were quantified in both batch and continuous culture systems simulating the human colon. The exponential growth of S. Typhimurium was halted when the population of Escherichia coli reached the maximum population density in a two-compartment co-culture system where the two species were separated by a 0.45 μm pore membrane. Furthermore, the growth of some gut bacteria such as Lactobacillus gasseri and Bifidobacterium bifidum was inhibited by the presence of S. Typhimurium in the other compartment.The survival of S. Typhimurium was severely affected in mixed batch cultures with human faecal samples; a reduction of 103–104 cfu/ml in the concentration of S. Typhimurium was observed in these cultures. However, no effect on S. Typhimurium survival was observed in mixed batch cultures with a simplified gut model microbiota under the same conditions.The effect of human faecal samples on S. Typhimurium in a three-stage continuous culture was different to that obtained in batch cultures; its growth rather than survival was affected under these conditions. S. Typhimurium growth was inhibited, and the bacterium was therefore eliminated by the continuous flow of the medium.Depending upon culturing conditions, the gut microbiota caused either growth inhibition, inactivation or did not affect S. Typhimurium.