Dra/AfaE adhesin of uropathogenic Dr/Afa+ Escherichia coli mediates mortality in pregnant rats

Pathogenomics and clinical recurrence influence biofilm capacity of Escherichia coli isolated from canine urinary tract infections

Biofilm formation enhances bacteria’s ability to colonize unique niches while protecting themselves from environmental stressors. Escherichia coli that colonize the urinary tract can protect themselves from the harsh bladder environment by forming biofilms. These biofilms promote persistence that can lead to chronic and recurrent urinary tract infections (UTI). While biofilm formation is frequently studied among urinary E. coli, its association with other pathogenic mechanisms and adaptations in certain host populations remains poorly understood. Here we utilized whole genome sequencing and retrospective medical record analysis to investigate associations between the population structure, phenotypic resistance, resistome, virulome, and patient demographic and clinical findings of 104 unique urinary E. coli and their capacity to form biofilms. We show that population structure including multilocus sequence typing and Clermont phylogrouping had no association with biofilm capacity. Among clinical factors, exposure to multiple antibiotics within that past 30 days and a clinical history of recurrent UTIs were positively associated with biofilm formation. In contrast, phenotypic antimicrobial reduced susceptibility and corresponding acquired resistance genes were negatively associated with biofilm formation. While biofilm formation was associated with increased virulence genes within the cumulative virulome, individual virulence genes did not influence biofilm capacity. We identified unique virulotypes among different strata of biofilm formation and associated the presence of the tosA/R-ibeA gene combination with moderate to strong biofilm formation. Our findings suggest that E. coli causing UTI in dogs utilize a heterogenous mixture of virulence genes to reach a biofilm phenotype, some of which may promote robust biofilm capacity. Antimicrobial use may select for two populations, non-biofilm formers that maintain an arsenal of antimicrobial resistance genes to nullify treatment and a second that forms durable biofilms to avoid therapeutic insults.

Differential Afa/Dr Fimbriae Expression in the Multidrug-Resistant Escherichia coli ST131 Clone

Many antibiotic resistant uropathogenic Escherichia coli (UPEC) strains belong to clones defined by their multilocus sequence type (ST), with ST131 being the most dominant. Although we have a good understanding of resistance development to fluoroquinolones and third-generation cephalosporins by ST131, our understanding of the virulence repertoire that has contributed to its global dissemination is limited. Here we show that the genes encoding Afa/Dr fimbriae, a group of adhesins strongly associated with UPEC that cause gestational pyelonephritis and recurrent cystitis, are found in approximately one third of all ST131 strains. Sequence comparison of the AfaE adhesin protein revealed a unique allelic variant carried by 82.9% of afa-positive ST131 strains. We identify the afa regulatory region as a hotspot for the integration of insertion sequence (IS) elements, all but one of which alter afa transcription. Close investigation demonstrated that the integration of an IS1 element in the afa regulatory region leads to increased expression of Afa/Dr fimbriae, promoting enhanced adhesion to kidney epithelial cells and suggesting a mechanism for altered virulence. Finally, we provide evidence for a more widespread impact of IS1 on ST131 genome evolution, suggesting that IS dynamics contribute to strain level microevolution that impacts ST131 fitness. IMPORTANCE E. coli ST131 is the most common antibiotic resistant UPEC clone associated with human urinary tract and bloodstream infections. Understanding the features of ST131 that have driven its global dissemination remains a critical priority if we are to counter its increasing antibiotic resistance. Here, we utilized a large collection of ST131 isolates to investigate the prevalence, regulation, and function of Afa/Dr fimbriae, a well-characterized UPEC colonization and virulence factor. We show that the afa genes are found frequently in ST131 and demonstrate how the integration of IS elements in the afa regulatory region modulates Afa expression, presenting an example of altered virulence capacity. We also exploit a curated set of ST131 genomes to map the integration of the antibiotic resistance-associated IS1 element in the ST131 pangenome, providing evidence for its widespread impact on ST131 genome evolution.

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.

Extraintestinal isolates ofEscherichia coli: identification and prospects for vaccine development

Extraintestinal pathogenic Escherichia coli (ExPEC) cause a wide variety of infections that are responsible for significant morbidity, mortality and costs to our healthcare system. Thereby, the development of an efficacious ExPEC vaccine will minimize disease and may be cost-effective in selected patient groups. Surface polysaccharides, such as capsule, have been traditional targets for vaccine development. Considering that significant antigenic heterogeneity exists among surface polysaccharides present in various ExPEC strains, their use as vaccine candidates will be challenging. Therefore, alternative vaccine candidates/approaches are being identified and evaluated and are discussed in this review. The authors envision that an efficacious ExPEC vaccine will consist of either a polyvalent subunit vaccine or a genetically engineered killed whole-cell vaccine.

Maternal/fetal mortality and fetal growth restriction: role of nitric oxide and virulence factors in intrauterine infection in rats

OBJECTIVE

The mechanism of infection-related deaths of pregnant rats and intrauterine growth restriction are not understood. We assessed whether nitric oxide (NO) has differential effects on infection with Escherichia coli Dr/Afa mutants that lack either AfaE or AfaD invasins.

STUDY DESIGN

Sprague-Dawley rats were infected intrauterinally with the clinical strain of E coli AfaE(+)D(+) or 1 of its isogenic mutants in the presence or absence of the NO synthesis inhibitor N(G)-nitro-L-arginine methyl ester (L-NAME). Maternal/fetal mortality rates, fetoplacental weight, and infection rates were evaluated.

RESULTS

Maternal and/or fetal death was associated with the presence of at least 1 virulence factor (AfaE(+)D(+)>AfaE(+)D(-)>AfaE(-)D(+)) and was increased by L-NAME treatment. The fetal and placental weights were lower than controls and were further reduced by L-NAME treatment.

CONCLUSION

These results demonstrate that NO enhanced AfaE- and AfaD-mediated virulence and plays an important role in Dr/Afa(+)E coli gestational tropism.

Adhesive organelles of Gram-negative pathogens assembled with the classical chaperone/usher machinery: structure and function from a clinical standpoint

This review summarizes current knowledge on the structure, function, assembly and biomedical applications of the superfamily of adhesive fimbrial organelles exposed on the surface of Gram-negative pathogens with the classical chaperone/usher machinery. High-resolution three-dimensional (3D) structure studies of the minifibers assembling with the FGL (having a long F1-G1 loop) and FGS (having a short F1-G1 loop) chaperones show that they exploit the same principle of donor-strand complementation for polymerization of subunits. The 3D structure of adhesive subunits bound to host-cell receptors and the final architecture of adhesive fimbrial organelles reveal two functional families of the organelles, respectively, possessing polyadhesive and monoadhesive binding. The FGL and FGS chaperone-assembled polyadhesins are encoded exclusively by the gene clusters of the γ3- and κ-monophyletic groups, respectively, while gene clusters belonging to the γ1-, γ2-, γ4-, and π-fimbrial clades exclusively encode FGS chaperone-assembled monoadhesins. Novel approaches are suggested for a rational design of antimicrobials inhibiting the organelle assembly or inhibiting their binding to host-cell receptors. Vaccines are currently under development based on the recombinant subunits of adhesins.

FGL chaperone-assembled fimbrial polyadhesins: anti-immune armament of Gram-negative bacterial pathogens

This review summarizes the current knowledge on the structure, function, assembly, and biomedical applications of the family of adhesive fimbrial organelles assembled on the surface of Gram-negative pathogens via the FGL chaperone/usher pathway. Recent studies revealed the unique structural and functional properties of these organelles, distinguishing them from a related family, FGS chaperone-assembled adhesive pili. The FGL chaperone-assembled organelles consist of linear polymers of one or two types of protein subunits, each possessing one or two independent adhesive sites specific to different host cell receptors. This structural organization enables these fimbrial organelles to function as polyadhesins. Fimbrial polyadhesins may ensure polyvalent fastening of bacteria to the host cells, aggregating their receptors and triggering subversive signals that allow pathogens to evade immune defense. The FGL chaperone-assembled fimbrial polyadhesins are attractive targets for vaccine and drug design.

Renal allograft injury is associated with urinary tract infection caused by Escherichia coli bearing adherence factors

Urinary tract infections are the most common infection in renal transplant patients and Escherichia coli (E. coli) is the most common clinical isolate. Although acute allograft injury (AAI) secondary to urinary tract infection (UTI) has been reported, the incidence of AAI associated with UTI, the virulence factors express by uropathic E. coli and whether virulence factors are associated with renal allograft outcome have not been described. We collected E. coli from our renal transplant patients with UTI, determined O:H serotypes, P and Dr fimbriae expression and the clinical presentation and allograft function during the UTI and post-UTI period. Pyelonephritis occurred in 40% of our patients, 82% of which had AAI (>20% increase in SCr). Sixty-two percent of E. coli isolates that expressed P fimbriae were associated with AAI, whereas only 29% that did not express P fimbriae had AAI (p = 0.03). The pattern of P fimbriae and O serotypes differed from reported isolates, as the P fimbriae PapG class II and the O25 serotype were the most common. Dr adhesin was expressed on 7 isolates, including 2 of 3 with urosepsis. We propose a unique pattern of uropathogenic serotypes and adherence factors contribute to acute allograft injury in renal transplant patients with UTI.

Diffusely adherent Escherichia coli strains expressing Afa/Dr adhesins (Afa/Dr DAEC): hitherto unrecognized pathogens

Diffusely adherent Escherichia coli (DAEC) strains are currently considered to constitute a putative sixth group of diarrheagenic E. coli. However, on the basis of their diffuse adherence to HEp-2 and HeLa cells, the detection of afa/dra/daa-related operons encoding this adherence phenotype, and the mobilization of decay-accelerating factor, both commensal and pathogenic strains can be classified as Afa/Dr DAEC isolates. Furthermore, strains associated with diarrheal diseases and strains causing extra-intestinal infections can also be identified as Afa/Dr DAEC strains. Although several cell signaling events that occur after epithelial cells have been infected by Afa/Dr DAEC have been reported, the pathophysiological processes that allow intestinal and extra-intestinal infections to develop are not fully understood. This review focuses on the genetic organization of the afa/dra/daa-related operons and on the virulence factors that trigger cellular responses, some of which are deleterious for the host cells. Finally, this review suggests future lines of research that could help to elucidate these questions.

Sticky fibers and uropathogenesis: bacterial adhesins in the urinary tract

Adhesins mediate the introduction of bacteria to the host in the sometimes life-long relationship of uropathogenic Esherichia coli (UPEC) and the human urinary tract. As a class of extracellular proteins, adhesins enable bacteria to adhere to and, in some cases, invade host tissue; adhesins render UPEC virulent and permit host colonization. Adhesin receptor interactions at the host interface determine tissue tropism and disease progression in that niche, with each adhesin preferring unique sites within the urinary tract. This review focuses on known adhesins implicated in uropathogenesis, the structural basis of tissue tropism, postinvasion intracellular replication, current therapeutic design strategies, and newly discovered fimbrial gene clusters that may play a role in urinary tract infections.