Complement protective epitopes and CD55-microtubule complexes facilitate the invasion and intracellular persistence of uropathogenic Escherichia coli

In Vivo Role of Two-Component Regulatory Systems in Models of Urinary Tract Infections

Two-component signaling systems (TCSs) are finely regulated mechanisms by which bacteria adapt to environmental conditions by modifying the expression of target genes. In bacterial pathogenesis, TCSs play important roles in modulating adhesion to mucosal surfaces, resistance to antibiotics, and metabolic adaptation. In the context of urinary tract infections (UTI), one of the most common types infections causing significant health problems worldwide, uropathogens use TCSs for adaptation, survival, and establishment of pathogenicity. For example, uropathogens can exploit TCSs to survive inside bladder epithelial cells, sense osmolar variations in urine, promote their ascension along the urinary tract or even produce lytic enzymes resulting in exfoliation of the urothelium. Despite the usefulness of studying the function of TCSs in in vitro experimental models, it is of primary necessity to study bacterial gene regulation also in the context of host niches, each displaying its own biological, chemical, and physical features. In light of this, the aim of this review is to provide a concise description of several bacterial TCSs, whose activity has been described in mouse models of UTI.

Estrogen receptor alpha differentially modulates host immunity in the bladder and kidney in response to urinary tract infection

The protective role of endogenous estrogen against Urinary Tract Infection (UTI) is well recognized, but the involvement of estrogen receptors (ERs) in modulating immunity in the urinary tract during UTI pathogenesis has not been investigated. The current study investigates the role of ERα in modulating immune responses and UTI outcome. Mice were pre-treated with either ERα agonist, propyl-pyrazole-triol (PPT), or ERα antagonist, methyl-piperidino-pyrazole (MPP), before experimental UTI. The UTI outcome was determined by checking the bacterial load, CD55 and TNFα expression in the bladder and kidney tissues. We observed opposite effects of PPT and MPP treatment on bacterial clearance in bladder versus kidney. PPT significantly reduced bacterial load (P < 0.05) only in the kidney, with minimal changes in CD55 and TNFα levels. In contrast, MPP showed remarkable bacterial clearance only in the bladder that corresponded with reduced CD55 and TNFα expression. MPP treatment in uninfected state induced a significant increase in TNFα production (P < 0.05) in the bladder, but not in the kidney. Our results suggest a protective role of ERα in the kidney. However, protection in the bladder may be mediated via other ER subtypes that may be involved in boosting the local immune responses. Drugs targeting specific ERs in bladder may serve as an adjunct treatment for boosting immune responses in the urogenital tract for efficient bacterial clearance.

Invasion of Host Cells and Tissues by Uropathogenic Bacteria

Within the mammalian urinary tract uropathogenic bacteria face many challenges, including the shearing flow of urine, numerous antibacterial molecules, the bactericidal effects of phagocytes, and a scarcity of nutrients. These problems may be circumvented in part by the ability of uropathogenic Escherichia coli and several other uropathogens to invade the epithelial cells that line the urinary tract. By entering host cells, uropathogens can gain access to additional nutrients and protection from both host defenses and antibiotic treatments. Translocation through host cells can facilitate bacterial dissemination within the urinary tract, while the establishment of stable intracellular bacterial populations may create reservoirs for relapsing and chronic urinary tract infections. Here we review the mechanisms and consequences of host cell invasion by uropathogenic bacteria, with consideration of the defenses that are brought to bear against facultative intracellular pathogens within the urinary tract. The relevance of host cell invasion to the pathogenesis of urinary tract infections in human patients is also assessed, along with some of the emerging treatment options that build upon our growing understanding of the infectious life cycle of uropathogenic E. coli and other uropathogens.

Validation of research trajectory 1 of an Exposome framework: Exposure to benzo(a)pyrene confers enhanced susceptibility to bacterial infection

The exposome provides a framework for understanding elucidation of an uncharacterized molecular mechanism conferring enhanced susceptibility of macrophage membranes to bacterial infection after exposure to the environmental contaminant benzo(a)pyrene, [B(a)P]. The fundamental requirement in activation of macrophage effector functions is the binding of immunoglobulins to Fc receptors. FcγRIIa (CD32a), a member of the Fc family of immunoreceptors with low affinity for immunoglobulin G, has been reported to bind preferentially to IgG within lipid rafts. Previous research suggested that exposure to B(a)P suppressed macrophage effector functions but the molecular mechanisms remain elusive. The goal of this study was to elucidate the mechanism(s) of B(a)P-exposure induced suppression of macrophage function by examining the resultant effects of exposure-induced insult on CD32-lipid raft interactions in the regulation of IgG binding to CD32. The results demonstrate that exposure of macrophages to B(a)P alters lipid raft integrity by decreasing membrane cholesterol 25% while increasing CD32 into non-lipid raft fractions. This robust diminution in membrane cholesterol and 30% exclusion of CD32 from lipid rafts causes a significant reduction in CD32-mediated IgG binding to suppress essential macrophage effector functions. Such exposures across the lifespan would have the potential to induce immunosuppressive endophenotypes in vulnerable populations.

Strengths and Limitations of Model Systems for the Study of Urinary Tract Infections and Related Pathologies

Urinary tract infections (UTIs) are some of the most common bacterial infections worldwide and are a source of substantial morbidity among otherwise healthy women. UTIs can be caused by a variety of microbes, but the predominant etiologic agent of these infections is uropathogenic Escherichia coli (UPEC). An especially troubling feature of UPEC-associated UTIs is their high rate of recurrence. This problem is compounded by the drastic increase in the global incidence of antibiotic-resistant UPEC strains over the past 15 years. The need for more-effective treatments for UTIs is driving research aimed at bettering our understanding of the virulence mechanisms and host-pathogen interactions that occur during the course of these infections. Surrogate models of human infection, including cell culture systems and the use of murine, porcine, avian, teleost (zebrafish), and nematode hosts, are being employed to define host and bacterial factors that modulate the pathogenesis of UTIs. These model systems are revealing how UPEC strains can avoid or overcome host defenses and acquire scarce nutrients while also providing insight into the virulence mechanisms used by UPEC within compromised individuals, such as catheterized patients. Here, we summarize our current understanding of UTI pathogenesis while also giving an overview of the model systems used to study the initiation, persistence, and recurrence of UTIs and life-threatening sequelae like urosepsis. Although we focus on UPEC, the experimental systems described here can also provide valuable insight into the disease processes associated with other bacterial pathogens both within the urinary tract and elsewhere within the host.

Pathogenesis of human diffusely adhering Escherichia coli expressing Afa/Dr adhesins (Afa/Dr DAEC): current insights and future challenges

The pathogenicity and clinical pertinence of diffusely adhering Escherichia coli expressing the Afa/Dr adhesins (Afa/Dr DAEC) in urinary tract infections (UTIs) and pregnancy complications are well established. In contrast, the implication of intestinal Afa/Dr DAEC in diarrhea is still under debate. These strains are age dependently involved in diarrhea in children, are apparently not involved in diarrhea in adults, and can also be asymptomatic intestinal microbiota strains in children and adult. This comprehensive review analyzes the epidemiology and diagnosis and highlights recent progress which has improved the understanding of Afa/Dr DAEC pathogenesis. Here, I summarize the roles of Afa/Dr DAEC virulence factors, including Afa/Dr adhesins, flagella, Sat toxin, and pks island products, in the development of specific mechanisms of pathogenicity. In intestinal epithelial polarized cells, the Afa/Dr adhesins trigger cell membrane receptor clustering and activation of the linked cell signaling pathways, promote structural and functional cell lesions and injuries in intestinal barrier, induce proinflammatory responses, create angiogenesis, instigate epithelial-mesenchymal transition-like events, and lead to pks-dependent DNA damage. UTI-associated Afa/Dr DAEC strains, following adhesin-membrane receptor cell interactions and activation of associated lipid raft-dependent cell signaling pathways, internalize in a microtubule-dependent manner within urinary tract epithelial cells, develop a particular intracellular lifestyle, and trigger a toxin-dependent cell detachment. In response to Afa/Dr DAEC infection, the host epithelial cells generate antibacterial defense responses. Finally, I discuss a hypothetical role of intestinal Afa/Dr DAEC strains that can act as "silent pathogens" with the capacity to emerge as "pathobionts" for the development of inflammatory bowel disease and intestinal carcinogenesis.

Identification of antigen Ag43 in uropathogenic Escherichia coli Dr+ strains and defining its role in the pathogenesis of urinary tract infections

Urinary tract infections (UTIs) caused by uropathogenic Escherichia coli (UPEC) are amongst the most common bacterial infectious diseases in the developed world. The urovirulence of UPEC is mainly associated with the surface-exposed fimbrial adhesins and adhesins of the autotransporter (AT) family. The best studied of these proteins is antigen Ag43 mediating cell aggregation, adhesion and biofilm development as the causes of chronic UTIs. The E. coli IH11128 Dr(+) (dra (+)) strain of the Dr/Afa(+) family of adhesins possesses two major surface-exposed virulence factors: Dr fimbrial polyadhesin and DraD protein (fimbrial tip subunit or protein component of the adhesive sheath). Here, we identified for the first time, to our knowledge, the agn43 gene encoding Ag43 in the WT clinical isolate of UPEC Dr(+) as a new virulence factor not yet tested. We also found that Dr fimbrial expression, which like Ag43 is under the control of a phase-variable mechanism, did not exclude Ag43 surface presentation. However, the presence of Dr fimbriae supported by other structures on the cell surface caused a physical neutralization of Ag43-mediated autoaggregation during in vitro growth. The fimbrial bundling further increased the distance between the adjacent Ag43(+) cells, thus preventing head-to-tail association between surface-exposed Ag43 subunits and their interactions with the host cells. The investigations showed that Ag43 did not act as a specific adhesin and invasin, conversely to the major virulence factors of E. coli Dr(+), but played significant roles in the viability and metabolic activity of bacterial cells forming biofilm, and in the survival of bacteria within invaded epithelial cells.

Molecular analysis of asymptomatic bacteriuria Escherichia coli strain VR50 reveals adaptation to the urinary tract by gene acquisition

Urinary tract infections (UTIs) are among the most common infectious diseases of humans, with Escherichia coli responsible for >80% of all cases. One extreme of UTI is asymptomatic bacteriuria (ABU), which occurs as an asymptomatic carrier state that resembles commensalism. To understand the evolution and molecular mechanisms that underpin ABU, the genome of the ABU E. coli strain VR50 was sequenced. Analysis of the complete genome indicated that it most resembles E. coli K-12, with the addition of a 94-kb genomic island (GI-VR50-pheV), eight prophages, and multiple plasmids. GI-VR50-pheV has a mosaic structure and contains genes encoding a number of UTI-associated virulence factors, namely, Afa (afimbrial adhesin), two autotransporter proteins (Ag43 and Sat), and aerobactin. We demonstrated that the presence of this island in VR50 confers its ability to colonize the murine bladder, as a VR50 mutant with GI-VR50-pheV deleted was attenuated in a mouse model of UTI in vivo. We established that Afa is the island-encoded factor responsible for this phenotype using two independent deletion (Afa operon and AfaE adhesin) mutants. E. coli VR50afa and VR50afaE displayed significantly decreased ability to adhere to human bladder epithelial cells. In the mouse model of UTI, VR50afa and VR50afaE displayed reduced bladder colonization compared to wild-type VR50, similar to the colonization level of the GI-VR50-pheV mutant. Our study suggests that E. coli VR50 is a commensal-like strain that has acquired fitness factors that facilitate colonization of the human bladder.

Decay-accelerating factor 1 deficiency exacerbates leptospiral-induced murine chronic nephritis and renal fibrosis

Leptospirosis is a global zoonosis caused by pathogenic Leptospira, which can colonize the proximal renal tubules and persist for long periods in the kidneys of infected hosts. Here, we characterized the infection of C57BL/6J wild-type and Daf1^−/− mice, which have an enhanced host response, with a virulent Leptospira interrogans strain at 14 days post-infection, its persistence in the kidney, and its link to kidney fibrosis at 90 days post-infection. We found that Leptospira interrogans can induce acute moderate nephritis in wild-type mice and is able to persist in some animals, inducing fibrosis in the absence of mortality. In contrast, Daf1^−/− mice showed acute mortality, with a higher bacterial burden. At the chronic stage, Daf1^−/− mice showed greater inflammation and fibrosis than at 14 days post-infection and higher levels at all times than the wild-type counterpart. Compared with uninfected mice, infected wild-type mice showed higher levels of IL-4, IL-10 and IL-13, with similar levels of α-smooth muscle actin, galectin-3, TGF-β1, IL-17, IFN-γ, and lower IL-12 levels at 90 days post-infection. In contrast, fibrosis in Daf1^−/− mice was accompanied by high expression of α-smooth muscle actin, galectin-3, IL-10, IL-13, and IFN-γ, similar levels of TGF-β1, IL-12, and IL-17 and lower IL-4 levels. This study demonstrates the link between Leptospira-induced murine chronic nephritis with renal fibrosis and shows a protective role of Daf1.