Interactions between salmonella typhimurium and human gut bacteria
Salmonella enterica subsp. enterica serovar Typhimurium is an important enteropathogen that causes human morbidity and mortality worldwide. It is essential to study the interaction between Salmonella and the gut bacteria to elucidate the elements that influence the ability of the pathogen to overcome the colonisation barrier mediated by the gut microbiota and why Salmonella can persist in ‘healthy’ individuals in a carrier state after infection. In this study the effect of faecal bacteria on the growth and survival of S. Typhimurium was investigated. Initially, experiments involved co-cultures of the pathogen and single strains of intestinal bacteria obtained from culture collections; results showed that when E. coli reached its maximum concentration density, the growth of S. Typhimurium was halted. S. Typhimurium was then inoculated with multi-strain gut bacteria from culture collections and also with faecal samples in batch cultures mimicking the conditions of the human colon. A significant reduction of S.Typhimurium concentration was observed in mixed cultures with faecal samples from different human donors; however, bacteria obtained from culture collection had no effect on S. Typhimurium. Close proximity with faecal bacteria was required as the pathogen was not affected when it was separated from the faecal bacteria by a 0.45 µm pore size membrane. S. Typhimurium was also affected in a continuous culture system. Transcriptomic analysis indicated that some of the functions associated with the genes expressed by S. Typhimurium during Salmonella inactivation were related to stress responses. Molecular profiling of faecal bacteria measured by denaturing gradient gel electrophoresis did not show any change specifically associated to S. Typhimurium inactivation. It was not possible to identify the bacterial strains responsible for the inactivation of S. Typhimurium; however, this effect caused by cell-cell contact with human faecal bacteria is reported for the first time in this study.
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