The Lyme disease agent Borrelia burgdorferi naturally persists in a cycle that primarily involves ticks and mammals. We have now identified a tick receptor (TROSPA) that is required for spirochetal colonization of Ixodes scapularis. B. burgdorferi outer surface protein A, which is abundantly expressed on spirochetes within the arthropod and essential for pathogen adherence to the vector, specifically bound to TROSPA. TROSPA mRNA levels in ticks increased following spirochete infestation and decreased in response to engorgement, events that are temporally linked to B. burgdorferi entry into and egress from the vector. The blockade of TROSPA by TROSPA antisera or by the repression of TROSPA expression via RNA interference reduced B. burgdorferi adherence to the I. scapularis gut in vivo, thereby preventing efficient colonization of the vector and subsequently reducing pathogen transmission to the mammalian host. Identification of an I. scapularis receptor for B. burgdorferi is the first step toward elucidating arthropod ligands that are required for survival of spirochetes in nature.

Proteus mirabilis, a common cause of urinary tract infections (UTI) in individuals with functional or structural abnormalities or with long-term catheterization, forms bladder and kidney stones as a consequence of urease-mediated urea hydrolysis. Known virulence factors, besides urease, are hemolysin, fimbriae, metalloproteases, and flagella. In this study we utilized the CBA mouse model of ascending UTI to evaluate the colonization of mutants of P. mirabilis HI4320 that were generated by signature-tagged mutagenesis. By performing primary screening of 2088 P. mirabilis transposon mutants, we identified 502 mutants that ranged from slightly attenuated to unrecoverable. Secondary screening of these mutants revealed that 114 transposon mutants were reproducibly attenuated. Cochallenge of 84 of these single mutants with the parent strain in the mouse model resulted in identification of 37 consistently out-competed P. mirabilis transposon mutants, 25 of which were out-competed >100-fold for colonization of the bladder and/or kidneys by the parent strain. We determined the sequence flanking the site of transposon insertion in 29 attenuated mutants and identified genes affecting motility, iron acquisition, transcriptional regulation, phosphate transport, urease activity, cell surface structure, and key metabolic pathways as requirements for P. mirabilis infection of the urinary tract. Two mutations localized to a approximately 42-kb plasmid present in the parent strain, suggesting that the plasmid is important for colonization. Isolation of disrupted genes encoding proteins with homologies to known bacterial virulence factors, especially the urease accessory protein UreF and the disulfide formation protein DsbA, showed that the CBA mouse model and mutant pools are a reliable source of attenuated mutants with mutations in virulence genes.

Proteus mirabilis is a common uropathogen in patients with long-term catheterization or with structural or functional abnormalities in the urinary tract. The mannose-resistant, Proteus-like (MR/P) ®mbriae and agellum are among virulence factors of P.mirabilis that contribute to its colonization in a murine model of ascending urinary tract infection. mrpJ, the last of nine genes of the mrp operon, encodes a 107 amino acid protein that contains a putative helix±turn±helix domain. Using transcriptional lacZ fusions integrated into the chromosome and mutagenesis studies, we demonstrate that MrpJ represses transcription of thē agellar regulon and thus reduces¯agella synthesis when MR/P ®mbriae are produced. The repression of agella synthesis by MrpJ is con®rmed by electron microscopy. However, a gel mobility shift assay indicates that MrpJ does not bind directly to the regulatory region of the¯hDC operon. The isogenic mrpJ null mutant of wild-type P.mirabilis strain HI4320 is attenuated in the murine model. Our data also indicate that PapX encoded by a pap (pyelonephritisassociated pilus) operon of uropathogenic Escherichia coli is a functional homolog of MrpJ.

No abstract