The lpf gene cluster for long polar fimbriae is not involved in adherence of enteropathogenic Escherichia coli or virulence of Citrobacter rodentium

Using the enteropathogenic Escherichia coli (EPEC) genome sequence, we found that EPEC E2348/69 has an lpfABCDE gene cluster homologous (about 60% identical at the protein level) to the Salmonella long polar fimbria (LPF) operon. To determine whether this operon is essential for adherence, the lpfABCD_E23 genes were deleted from EPEC strain E2348/69 by allelic exchange. Analysis of the resulting EPECΔlpfABCD_E23 strain showed no change in adherence to HeLa cells or to human intestinal biopsy cells in the in vitro organ culture (FVOC) system compared to the wild type. Sera from volunteers experimentally infected with E2348/69 showed no antibody response to the major subunit protein, LpfA. These results suggested that the lpf _E23 gene cluster is not necessary for EPEC adherence and attaching/effacing (A/E) lesion formation on human biopsy samples and is not expressed during human infection. We also identified an lpf gene cluster in Citrobacter rodentium strain ICC168 (lpf_cr). A ΔlpfA _cr mutant of ICC168 retained wild-type adherence and A/E lesion-forming activity on HeLa cells. C3H/HeJ mice were infected with a wild-type C. rodentium strain and its lpfA_cr isogenic mutant. Both strains were recovered at high levels in stools, and there were no significant differences between the groups both in terms of the number of CFU/organ (colon and cecum) and in terms of the amount of hyperplasia, as measured by weight. Similar results were observed in a second mouse strain, C57BL/6. These data suggest that in addition to playing no apparent role in EPEC pathogenesis, lpf_cr is not required for C. rodentium virulence in either the C3H/HeJ or C57BL/6 mouse model.