Bacterial infection has been linked to carcinogenesis, however, there is lack of knowledge of molecular mechanisms that associate infection with the development of cancer. We analyzed possible effects of the consumption of heat-killed E. coli O157:H7 cells or its cellular components, DNA, RNA, protein or lipopolysaccharides (LPS) on gene expression in naïve liver cells. Four week old mice were provided water supplemented with whole heat-killed bacteria or bacterial components for a two week period. One group of animals was sacrificed immediately, whereas another group was allowed to consume uncontaminated tap water for an additional two weeks, and liver samples were collected, post mortem. Liver cells responded to exposure of whole heat-killed bacteria and LPS with alteration in γH2AX levels and levels of proteins involved in proliferation, DNA methylation (MeCP2, DNMT1, DNMT3A and 3B) or DNA repair (APE1 and KU70) as well as with changes in the expression of genes involved in stress response, cell cycle control and bile acid biosynthesis. Other bacterial components analysed in this study did not lead to any significant changes in the tested molecular parameters. This study suggests that lipopolysaccharides are a major component of Gram-negative bacteria that induce molecular changes within naïve cells of the host.

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Previous research showed that the consumption of heat-killed E. coli O157:H7 bacteria resulted in an increase in the level of DNA damage in intestine, liver and spleen cells. We hypothesized that certain bacterial components released from heat-killed bacteria trigger this response. We analysed the possibility that bacterial components [such as lipopolysaccharides (LPS)] could induce changes in the level of proteins involved in cell proliferation, DNA repair and DNA methylation in distal spleen tissues of mice. Four-week-old male mice were provided water supplemented with whole heat-killed E. coli O157:H7 bacteria or components of bacteria (DNA, RNA, proteins and LPS). Spleen cells responded to exposure to whole heat-killed bacteria and LPS with an alteration in the level of PCNA proteins, DNA methylation proteins (DNMT1, DNMT3A, DNMT3B, and MeCP2) and DNA repair proteins (APE1 and KU70). Other bacterial components analysed in this study mostly did not alter protein expression. The data suggest that LPS is a bacterial component capable of inducing molecular changes in naïve spleen cells of hosts exposed to it.