Finding regulators associated with the expression of the long polar fimbriae in enteropathogenic Escherichia coli

Enteropathogenic Escherichia coli (EPEC) is a human pathogen that requires initial adhesion to the intestine in order to cause disease. Multiple adhesion factors have been identified in E. coli strains, among them the long polar fimbriae (Lpf), a colonization factor associated with intestinal adhesion. The conditions of Lpf expression are well understood in enterohemorrhagic E. coli (EHEC); however, the expression of EPEC lpf has been found to be repressed under any in vitro condition tested. Therefore, we decided to identify those factors silencing expression of EPEC lpf. Because histone-like nucleoid structuring protein (H-NS) is a known repressor of EHEC lpf, we tested it and found that H-NS is a repressor of EPEC lpf. We also found that the adhesion of the EPEC Δhns strain was significantly enhanced compared to the wild-type strain. Because lpf expression was modestly increased in the hns mutant, transposon mutagenesis was performed to find a strain displaying higher lpf expression than EPEC Δhns. One Tn5 insertion was identified within the yhjX gene, and further in vitro characterization revealed increased lpf expression and adhesion to Caco-2 cells compared with EPEC Δhns. However, in a murine model of intestinal infection, the EPEC Δhns and EPEC Δhns Tn5 mutants had only a slight change in colonization pattern compared to the wild-type strain. Our data showed that EPEC Lpf is transcribed, but its role in EPEC intestinal colonization requires further analysis.