Protective effects of Lactobacilli, Bifidobacteria and Staphylococci on the infection of cultured HT29 cells with different enterohemorrhagic Escherichia coli serotypes are strain-specific

Abstract

In this study, we investigated the interaction of 19 benign strains of lactic acid bacteria (LAB), bifidobacteria and staphylococci with enterohemorrhagic Escherichia coli (EHEC) strains of different serotypes and virulence gene spectrum in a HT29 cell culture infection model. As markers of infection, the secretion of interleukin 8 (IL-8) and the activation of the transcription factor NF-κB by the infected cells were determined. With 12 of 19 tested strains, a weak reduction < 30% of IL-8 secretion of HT29 cells after co-infection with EHEC O157:H7 strain EDL933 was observed. Six strains reduced the IL-8 secretion up to 60% and the strain B. adolescentis DSMZ 20086 decreased the IL-8 production about 73%. In further co-infection assays with EHEC strains of the serotypes O103:H2, O26:H −, 0157:H − and O113:H21, different abilities of the LAB strains to influence the infection with the different EHEC strains were noted. Therefore, the protective anti-inflammatory effect is strain specific for LAB and also depends on the application of EHEC strains with different sero- and virulence types. The differences in efficacy of protective bacteria against certain EHEC strains were unexpected and have not been shown so far. Furthermore, we could show that the inhibitory effects were not attributed to lower adhesion abilities of EHEC to the production of organic acids by the benign bacteria. In addition, viable bacteria are needed to inhibit the IL-8 secretion. Moreover, the NF-κB activation was reduced significantly by all tested LAB strains in co-infection trials, but was not strain-specific. The model described here is useful to screen for basic effects of protective bacteria that are able to counteract EHEC-mediated effects on human cells, and to study the molecular interaction between bacteria as well as between bacteria and human cultured cells.