Iron plays an important role on the expression regulation of many virulence genes in pathogenic bacteria. This regulation is mediated by the transcriptional regulator Fur which complexes with iron and binds to specific sequences, named Fur boxes, located in the promoter region of target genes, leading to the transcriptional induction or repression of these genes. Klebsiella pneumoniae is a gram-negative opportunistic pathogen responsible for infections in the gastrointestinal, respiratory and genitourinary tracts. Virulence factors identified in K. pneumoniae include the production of lipopolysaccharide (LPS) and capsule polysaccharide (CPS), and the expression of type 1 and type 3 fimbrial adhesins. Both LPS and CPS confer protection against phagocytosis and bactericidal action of human serum. Fimbriae assist in the process of adhesion to host cells and biofilm formation on abiotic surfaces. In K. pneumoniae type 1 fimbria plays a critical step in urinary tract infection due to its dual role in mediating not only adherence to urothelial cells, but also in triggering the host cell invasion. Once in the intracellular environment, bacteria replicate rapidly, forming an intracellular bacterial community. Among the genes that regulate fimbriae production in K. pneumoniae is fimZ, which encodes a putative transcriptional activator of type 1 fimbrial expression. Preliminary results indicated a Fur box on the promoter region of fimZ, thus revealing that the expression of type 1 fimbriae may be controlled by iron through the Fur regulator. However, little is known about the role of fimZ in the expression regulation of fimbriae and in the processes of host cells adhesion and invasion. Furthermore, the molecular basis of adhesion and invasion mediated by type 1 fimbriae in K. pneumoniae are still poorly understood, especially the mechanisms involved in the replication and persistence of the pathogen in the intracellular environment and the virulence genes required for adaptation in this environment. Thus, the aim of this study is to characterize the genotypic and phenotypic profiles of K. pneumoniae clinical isolates from urinary tract infections, and investigate the role of iron and fimZ in the processes of adhesion, invasion and intracellular replication of Klebsiella pneumoniae in human bladder epithelial cells.
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