Showing papers by "Scott J. Hultgren published in 2003"

Intracellular bacterial biofilm-like pods in urinary tract infections

Abstract: Escherichia coli entry into the bladder is met with potent innate defenses, including neutrophil influx and epithelial exfoliation. Bacterial subversion of innate responses involves invasion into bladder superficial cells. We discovered that the intracellular bacteria matured into biofilms, creating pod-like bulges on the bladder surface. Pods contained bacteria encased in a polysaccharide-rich matrix surrounded by a protective shell of uroplakin. Within the biofilm, bacterial structures interacted extensively with the surrounding matrix, and biofilm associated factors had regional variation in expression. The discovery of intracellular biofilm-like pods explains how bladder infections can persist in the face of robust host defenses.

Toll-like receptor 4 on stromal and hematopoietic cells mediates innate resistance to uropathogenic Escherichia coli

Abstract: Innate host defenses at mucosal surfaces are critical in the early stages of many bacterial infections. In addition to cells of the traditional innate immune system, epithelial cells can also produce inflammatory mediators during an infection. However, the role of the epithelium in innate host defense in vivo is unclear. Recent studies have shown that lipopolysaccharide (LPS) recognition is critical for bladder epithelial cells to recognize and respond to Escherichia coli. Moreover, the LPS-nonresponsive mouse strain C3H/HeJ, which has a mutation in the primary LPS receptor, Toll-like receptor 4 (TLR4), is extremely susceptible to infection with uropathogenic strains of E. coli. In this study, a bone marrow transplant approach was used to investigate the specific contributions of the bladder epithelium (and other stromal cells) in the TLR4-mediated innate immune response to the invading E. coli pathogen. Mice expressing the mutant TLR4 in the epithelial/stromal compartment were not able to mount a protective inflammatory response to control the early infection even when their hematopoietic cells expressed wild-type TLR4. However, the presence of TLR4+ epithelial/stromal cells was not sufficient to activate an acute inflammatory response unless the hematopoietic cells were also TLR4+. These results demonstrated that bladder epithelial cells play a critical role in TLR4-mediated innate immunity in vivo during a mucosal bacterial infection.

CD14- and Toll-like receptor-dependent activation of bladder epithelial cells by lipopolysaccharide and type 1 piliated Escherichia coli.

Abstract: The gram-negative bacterium Escherichia coli is the leading cause of urinary tract infection. The interaction between type 1 piliated E. coli and bladder epithelial cells leads to the rapid production of inflammatory mediators, such as interleukin-6 (IL-6) and IL-8. Conflicting reports have been published in the literature regarding the mechanism by which uroepithelial cells are activated by type 1 piliated E. coli. In particular, the role of lipopolysaccharide (LPS) in these responses has been an area of significant debate. Much of the data arguing against LPS-mediated activation of bladder epithelial cells have come from studies using a renal epithelial cell line as an in vitro model of the urinary epithelium. In this report, we analyzed three bladder epithelial cell lines and demonstrated that they all respond to LPS. Furthermore, the LPS responsivity of the cell lines directly correlated with their ability to generate IL-6 after E. coli stimulation. The LPS receptor complex utilized by the bladder epithelial cell lines included CD14 and Toll-like receptors, and signaling involved the activation of NF-κB and p38 mitogen-activated protein kinase. Also, reverse transcription-PCR analysis demonstrated that bladder epithelial cells express CD14 mRNA. Thus, the molecular machinery utilized by bladder epithelial cells for the recognition of E. coli is very similar to that described for traditional innate immune cells, such as macrophages. In contrast, the A498 renal epithelial cell line did not express CD14, was hyporesponsive to LPS stimulation, and demonstrated poor IL-6 responses to E. coli.

Chaperone-Subunit-Usher Interactions Required for Donor Strand Exchange during Bacterial Pilus Assembly

Abstract: The assembly of type 1 pili on the surface of uropathogenic Escherichia coli proceeds via the chaperone-usher pathway. Chaperone-subunit complexes interact with one another via a process termed donor strand complementation whereby the G1β strand of the chaperone completes the immunoglobulin (Ig) fold of the pilus subunit. Chaperone-subunit complexes are targeted to the usher, which forms a channel across the outer membrane through which pilus subunits are translocated and assembled into pili via a mechanism known as donor strand exchange. This is a mechanism whereby chaperone uncapping from a subunit is coupled with the simultaneous assembly of the subunit into the pilus fiber. Thus, in the pilus fiber, the N-terminal extension of every subunit completes the Ig fold of its neighboring subunit by occupying the same site previously occupied by the chaperone. Here, we investigated details of the donor strand exchange assembly mechanism. We discovered that the information necessary for targeting the FimC-FimH complex to the usher resides mainly in the FimH protein. This interaction is an initiating event in pilus biogenesis. We discovered that the ability of an incoming subunit (in a chaperone-subunit complex) to participate in donor strand exchange with the growing pilus depended on a previously unrecognized function of the chaperone. Furthermore, the donor strand exchange assembly mechanism between subunits was found to be necessary for subunit translocation across the outer membrane usher.

Stereoselective synthesis of optically active bicyclic β-lactam carboxylic acids that target pilus biogenesis in pathogenic bacteria

Abstract: Optically active bicyclic β-lactams were synthesized, starting from 2-H-Δ2-thiazolines and Meldrum's acid derivatives. Several methods to accomplish an ester hydrolysis without damaging the β-lactam framework were investigated. A rapid CsOH saponification of the β-lactam methyl esters was developed and protonation of the Cs-carboxylates by Amberlite (IR-120 H+) afforded a series of bicyclic β-lactam carboxylic acids. Moreover, a convenient method for the synthesis of 2-H-Δ2-thiazolinecarboxylic acid methyl ester 2 was developed. Bicyclic β-lactam carboxylic acids 7a–g and aldehydes 4a–d were screened for their affinity to the bacterial periplasmic chaperone PapD using a surface plasmon resonance technique. β-Lactams substituted with large acyl substituents showed better binding to the chaperone than the native C-terminal peptide PapG 8, demonstrating that bicyclic β-lactams constitute a new class of potential bacterial chaperone inhibitors.

Assembly of Adhesive Organelles on Gram-Negative Bacteria

Abstract: Bacterial pathogens interact with their hosts in a multitude of ways in order to persist, survive and multiply. The molecular signals triggered by these interactions, ultimately determines the fate of the microbe and the consequences to the host. The interaction between a microbe and its host often depends on the presentation of adhesins on the microbial surface. Adhesins are often assembled into hair-like fibers called pili (Fig. 1). Bacterial adhesins bind with stereochemical specificity to host receptors, thus targeting the bacteria to a defined niche within the environment. For example, pili facilitate intimate contact with eukaryotic cells resulting in the colonization of the cell surface, or invasion to gain access to a nutritionally rich environment within the eukaryotic cell allowing evasion of the host defenses. In host-pathogen interactions pili often activate a cascade of events that will ultimately determine whether the microbe will remain extracellular or trigger processes that will allow its uptake into host cells and/or activation of host defense mechanisms.