B-166. Regulation of Uropathogenic Escherichia coli Fim Gene Expression by Acid Tolerance Gene Products

W. R. Schwan1, J. Luedtke1, A. Wheaton1, M. Cheng1, J. W. Foster2, R. Wolchak1;
1Univ. Wisconsin, La Crosse, WI, 2Univ. South Alabama College of Med., Mobile, AL.

Each year in the United States, uropathogenic Escherichia coli (UPEC) cause thousands of urinary tract infections at a cost of billions of dollars. The ability to adhere to uroepithelial cells is critical for UPEC infections. Strains of UPEC possess type 1 pili to allow their adherence to bladder epithelial cells in the human and murine urinary tracts. Within the urinary tract, osmolality and pH can widely vary. Previous work has shown that an acidic pH adversely affects the expression of type 1 pili. To determine if acid tolerance gene products may be regulating E. coli fim gene expression and in turn type 1 pilus expression, a bank of K-12 strain acid tolerance gene mutants were screened using fimA-lacZ, fimB-lacZ, and fimE-lacZ fusions on single copy number plasmids. From β-galactosidase assay analyses, we have determined that a mutation in gadE de-repressed expression of all three fim genes, suggesting that GadE may be acting as a repressor in a low pH environment. Complementation of the gadE mutation caused even greater repression of the three fim genes than observed for the wild type strain. Moreover, mutations in gadX and cya also affected expression of the fim genes. To verify the role that GadE may play in type 1 pilus expression in a UPEC clinical isolate, a gadE mutation was constructed in UPEC strain NU149. The gadE mutation led to higher fim gene transcript levels and a higher frequency of phase ON bacteria as determined by PCR. In addition, enzyme immunoassays detected greater type 1 pilus expression in strain NU149 GadE when cultured in low pH medium as compared to the wild type bacteria. Again, complementation of the gadE mutation brought the transcription and protein expression back to wild type levels. The data demonstrate that UPEC fim genes are regulated directly or indirectly by the GadE protein and this could have some future bearing on the ability to prevent urinary tract infections by acidifying the urine and shutting off fim gene expression.