Uropathogenic Escherichia coli (UPEC) are a leading cause of urinary tract infections and virulence factors play a key role in pahogenesis - fimbriea, toxins such as hemolysin and iron uptake systems such as aerobactin, being the most common. The expression of virulence factor genes might be heterogenic, meaning that all genetically identical cells in a population, do not express the same genes. It is belived that heterogeneity is affected by differences in rates of translation, transcription and DNA topology. To further understand the expression of virulence factor genes we constructed gene fusions using the pBAC plasmid, the gfp gene for the Gfp fluorescent protein without its promoter and fimA, hlyA and iucD promotors for fimbriae, hemolysin and aerobactin, respectively. Using fluorescent microscopy and a variety of different growth conditions we were able to study gene expression at a single cell level. The employed growth media were: rich LB medium, minimal media with an added iron chelating ligand, as well as a low pH medium, all in liquid and firm form. Results showed higher promotor iucD expression when cells were grown on minimal media with iron deficiency, whereas the fimA fimbriae promotor showed higher expression upon growth on rich medium. In principle, expression was found to be homogenous however, an example of heterogenous expression of iucD was observed under noninducing conditions.
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