Novel three-dimensional organoid model for evaluation of the interaction of uropathogenic Escherichia coli with terminally differentiated human urothelial cells

Avian pathogenic Escherichia coli (APEC): current insights and future challenges

Avian pathogenic Escherichia coli (APEC) causes colibacillosis in avian species, and new investigations have implicated APEC as a possible foodborne zoonotic pathogen. This review analyzes APEC's pathogenic and virulence features, assesses the zoonotic potential, provides an update on antibiotic resistance and vaccine research efforts, and outlines alternate management approaches. Aside from established virulence factors, various additional components, including 2-component systems (TCS), adhesins, secretion systems (SS), invasions, iron acquisition systems, quorum sensing systems (QS), transcriptional regulators (TR), toxins, and genes linked with metabolism, contribute to APEC pathogenesis. APEC may spread to diverse species of birds in all business sectors and can infect birds of varying ages. However, younger birds experience more severe sickness than mature ones, probably due to their developing immune systems, and stress factors such as vaccination, Mycoplasma Infections, poor housing circumstances, respiratory viruses, and other risk factors for secondary infections can all make APEC both primary and secondary pathogens. Understanding these factors will help in generating new and effective treatments. Moreover, APEC O145 was the most prevalent serotype recently reported in all of China. Thus, the APEC's zoonotic potential should not be underrated. Furthermore, it has already been noted that APEC is resistant to almost all antibiotic classes, including carbapenems. A robust vaccine capable of protecting against multiple APEC serotypes is urgently needed. Alternative medications, particularly virulence inhibitors, can provide a special method with a decreased likelihood of acquiring resistance.

Advances in experimental bladder models: bridging the gap between in vitro and in vivo approaches for investigating urinary tract infections

Urinary tract infections (UTIs) pose a substantial burden on global healthcare systems. When unraveling the complex pathophysiology of UTIs, bladder models are used to understand complex and multifaceted interactions between different components within the system. This review aimed to bridge the gap between in vitro and in vivo experimental bladder models towards UTI research. We reviewed clinical, animal, and analytical studies and patents from 1959 to the end of 2023. Both in vivo and in vitro models offer unique benefits and drawbacks in understanding UTIs. In vitro models provide controlled environments for studying specific aspects of UTI biology and testing potential treatments, while in vivo models offer insights into how UTIs manifest and progress within living organisms. Thus, both types of models are leading to the development of more effective diagnostic tools and therapeutic interventions against UTIs. Moreover, advanced methodologies involving three-dimensional bladder organoids have also been used to study bladder biology, model bladder-related disorders, and explore new treatments for bladder cancers, UTIs, and urinary incontinence. Narrowing the distance between fundamental scientific research and practical medical applications, these pioneering models hold the key to unlocking new avenues for the development of personalized diagnostics, precision medicine, and ultimately, the alleviation of UTI-related morbidity worldwide.

A human urothelial microtissue model reveals shared colonization and survival strategies between uropathogens and commensals

Urinary tract infection is among the most common infections worldwide, typically studied in animals and cell lines with limited uropathogenic strains. Here, we assessed diverse bacterial species in a human urothelial microtissue model exhibiting full stratification, differentiation, innate epithelial responses, and urine tolerance. Several uropathogens invaded intracellularly, but also commensal Escherichia coli, suggesting that invasion is a shared survival strategy, not solely a virulence hallmark. The E. coli adhesin FimH was required for intracellular bacterial community formation, but not for invasion. Other shared lifestyles included filamentation (Gram-negatives), chaining (Gram-positives), and hijacking of exfoliating cells, while biofilm-like aggregates were formed mainly with Pseudomonas and Proteus. Urothelial cells expelled invasive bacteria in Rab-/LC3-decorated structures, while highly cytotoxic/invasive uropathogens, but not commensals, disrupted host barrier function and strongly induced exfoliation and cytokine production. Overall, this work highlights diverse species-/strain-specific infection strategies and corresponding host responses in a human urothelial microenvironment, providing insights at the microtissue, cell, and molecular level.

Cell Line-Based Human Bladder Organoids with Bladder-like Self-Organization-A New Standardized Approach in Bladder Cancer Research

Three-dimensional tumor models have gained significant importance in bladder cancer (BCa) research. Organoids consisting of different cell types better mimic solid tumors in terms of 3D architecture, proliferation, cell-cell interaction and drug responses. We developed four organoids from human BCa cell lines with fibroblasts and smooth muscle cells of the bladder, aiming to find models for BCa research. The organoids were characterized in terms of cytokeratins, vimentin, α-actin and KI67 by immunoreactivity. Further, we studied ligand-dependent activation of the Wnt/β-catenin pathway and investigated the responses to anti-tumor therapies. The organoids mimicked the structure of an inverse bladder wall, with outside urothelial cells and a core of supportive cells. The cytokeratin staining patterns and proliferation rate were in conjunction with the origins of the BCa cells. RT-112 even showed stratification of the epithelium. Treatment with Wnt10B led to increased β-catenin (active) levels in high-grade organoids, but not in low-grade BCa cells. Doxorubicin treatment resulted in clearly reduced viability (10-30% vs. untreated). In contrast, the effectivity of radiotherapy depended on the proliferation status of BCa cells. In conclusion, cell-line-based organoids can form bladder-like structures and reproduce in vivo features such as urothelial differentiation and stratification. Thus, they can be useful tools for functional studies in BCa and anti-cancer drug development.

Flourishing tumor organoids: History, emerging technology, and application

Malignant tumors are one of the leading causes of death which impose an increasingly heavy burden on all countries. Therefore, the establishment of research models that closely resemble original tumor characteristics is crucial to further understanding the mechanisms of malignant tumor development, developing safer and more effective drugs, and formulating personalized treatment plans. Recently, organoids have been widely used in tumor research owing to their advantages including preserving the structure, heterogeneity, and cellular functions of the original tumor, together with the ease of manipulation. This review describes the history and characteristics of tumor organoids and the synergistic combination of three-dimensional (3D) culture approaches for tumor organoids with emerging technologies, including tissue-engineered cell scaffolds, microfluidic devices, 3D bioprinting, rotating wall vessels, and clustered regularly interspaced short palindromic repeats-CRISPR-associated protein 9 (CRISPR-Cas9). Additionally, the progress in research and the applications in basic and clinical research of tumor organoid models are summarized. This includes studies of the mechanism of tumor development, drug development and screening, precision medicine, immunotherapy, and simulation of the tumor microenvironment. Finally, the existing shortcomings of tumor organoids and possible future directions are discussed.

An immunoresponsive three-dimensional urine-tolerant human urothelial model to study urinary tract infection

Introduction

Murine models of urinary tract infection (UTI) have improved our understanding of host-pathogen interactions. However, given differences between rodent and human bladders which may modulate host and bacterial response, including certain biomarkers, urothelial thickness and the concentration of urine, the development of new human-based models is important to complement mouse studies and to provide a more complete picture of UTI in patients.

Methods

We originally developed a human urothelial three-dimensional (3D) model which was urine tolerant and demonstrated several urothelial biomarkers, but it only achieved human thickness in heterogenous, multi-layered zones and did not demonstrate the comprehensive differentiation status needed to achieve barrier function. We optimised this model by altering a variety of conditions and validated it with microscopy, flow cytometry, transepithelial electrical resistance and FITC-dextran permeability assays to confirm tissue architecture, barrier integrity and response to bacterial infection.

Results

We achieved an improved 3D urine-tolerant human urothelial model (3D-UHU), which after 18-20 days of growth, stratified uniformly to 7-8 layers comprised of the three expected, distinct human cell types. The apical surface differentiated into large, CD227+ umbrella-like cells expressing uroplakin-1A, II, III, and cytokeratin 20, all of which are important terminal differentiation markers, and a glycosaminoglycan layer. Below this layer, several layers of intermediate cells were present, with a single underlying layer of CD271+ basal cells. The apical surface also expressed E-cadherin, ZO-1, claudin-1 and -3, and the model possessed good barrier function. Infection with both Gram-negative and Gram-positive bacterial classes elicited elevated levels of pro-inflammatory cytokines and chemokines characteristic of urinary tract infection in humans and caused a decrease in barrier function.

Discussion

Taken together, 3D-UHU holds promise for studying host-pathogen interactions and host urothelial immune response.

A Biomimetic Porcine Urothelial Model for Assessing Escherichia coli Pathogenicity

Urinary tract infections can be severe, sometimes fatal, diseases whose etiological pathogens are predominantly uropathogenic strains of E. coli (UPEC). To investigate the UPEC pathogenesis, several models have already been established with minor or major disadvantages. The aim was to develop a simple, fast, and inexpensive biomimetic in vitro model based on normal porcine urothelial (NPU) cells that are genetically and physiologically similar to human bladder urothelium and to perform basic studies of E. coli pathogenicity. Initially, the model was tested using a set of control E. coli strains and, subsequently, with human E. coli strains isolated either from patients with urinary infections or from the feces of healthy individuals. A drop in viability of NPU cells was used as a measure of the pathogenicity of the individual strain tested. To visualize the subcellular events, transmission and scanning electron microscopy was performed. The strains were tested for the presence of different virulence-associated genes, phylogroup, type of core lipid, O-serotype, and type of lipopolysaccharide and a statistical analysis of possible correlations between strains’ characteristics and the effect on the model was performed. Results showed that our model has the discriminatory power to distinguish pathogenic from non-pathogenic E. coli strains, and to identify new, potentially pathogenic strains.

Three-Dimensional Cell Culture Models to Study Respiratory Virus Infections Including COVID-19

Respiratory viral infections, including severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), are among the most common illnesses and a leading cause of morbidity and mortality worldwide. Due to the severe effects on health, the need of new tools to study the pathogenesis of respiratory viruses as well as to test for new antiviral drugs and vaccines is urgent. In vitro culture model systems, such as three-dimensional (3D) cultures, are emerging as a desirable approach to understand the virus host interactions and to identify novel therapeutic agents. In the first part of the article, we address the various scaffold-free and scaffold-based 3D culture models such as hydrogels, bioreactors, spheroids and 3D bioprinting as well as present their properties and advantages over conventional 2D methods. Then, we review the 3D models that have been used to study the most common respiratory viruses including influenza, parainfluenza, respiratory syncytial virus (RSV) and coronaviruses. Herein, we also explain how 3D models have been applied to understand the novel SARS-CoV-2 infectivity and to develop potential therapies.

Flagella, Type I Fimbriae and Curli of Uropathogenic Escherichia coli Promote the Release of Proinflammatory Cytokines in a Coculture System

BACKGROUND

Urinary tract infections (UTIs) are a public health problem in Mexico, and uropathogenic Escherichia coli (UPEC) is one of the main etiological agents. Flagella, type I fimbriae, and curli promote the ability of these bacteria to successfully colonize its host.

AIM

This study aimed to determine whether flagella-, type I fimbriae-, and curli-expressing UPEC induces the release of proinflammatory cytokines in an established coculture system.

METHODS

The fliC, fimH, and csgA genes by UPEC strain were disrupted by allelic replacement. Flagella, type I fimbriae, and curli were visualized by transmission electron microscopy (TEM). HTB-5 (upper chamber) and HMC-1 (lower chamber) cells cocultured in Transwell® plates were infected with these UPEC strains and purified proteins. There was adherence to HTB-5 cells treated with different UPEC strains and they were quantified as colony-forming units (CFU)/mL.

RESULTS

High concentrations of IL-6 and IL-8 were induced by the FimH and FliC proteins; however, these cytokines were detected in low concentrations in presence of CsgA. Compared with UPEC CFT073, CFT073ΔfimH, CFT073ΔfimHΔfliC, and CFT073ΔcsgAΔfimH strains significantly reduced the adherence to HTB-5 cells.

CONCLUSION

The FimH and FliC proteins are involved in IL-6 and IL-8 release in a coculture model of HTB-5 and HMC-1 cells.

Retinal organoids on-a-chip: a micro-millifluidic bioreactor for long-term organoid maintenance

Retinal degeneration is a leading cause of vision impairment and blindness worldwide and medical care for advanced disease does not exist. Stem cell-derived retinal organoids (RtOgs) became an emerging tool for tissue replacement therapy. However, existing RtOg production methods are highly heterogeneous. Controlled and predictable methodology and tools are needed to standardize RtOg production and maintenance. In this study, we designed a shear stress-free micro-millifluidic bioreactor for nearly labor-free retinal organoid maintenance. We used a stereolithography (SLA) 3D printer to fabricate a mold from which Polydimethylsiloxane (PDMS) was cast. We optimized the chip design using in silico simulations and in vitro evaluation to optimize mass transfer efficiency and concentration uniformity in each culture chamber. We successfully cultured RtOgs at three different differentiation stages (day 41, 88, and 128) on an optimized bioreactor chip for more than 1 month. We used different quantitative and qualitative techniques to fully characterize the RtOgs produced by static dish culture and bioreactor culture methods. By analyzing the results from phase contrast microscopy, single-cell RNA sequencing (scRNA seq), quantitative polymerase chain reaction (qPCR), immunohistology, and electron microscopy, we found that bioreactor-cultured RtOgs developed cell types and morphology comparable to static cultured ones and exhibited similar retinal genes expression levels. We also evaluated the metabolic activity of RtOgs in both groups using fluorescence lifetime imaging (FLIM), and found that the outer surface region of bioreactor cultured RtOgs had a comparable free/bound NADH ratio and overall lower long lifetime species (LLS) ratio than static cultured RtOgs during imaging. To summarize, we validated an automated micro-millifluidic device with significantly reduced shear stress to produce RtOgs of comparable quality to those maintained in conventional static culture.

Escherichia coli Alpha-Hemolysin HlyA Induces Host Cell Polarity Changes, Epithelial Barrier Dysfunction and Cell Detachment in Human Colon Carcinoma Caco-2 Cell Model via PTEN-Dependent Dysregulation of Cell Junctions

Escherichia coli (E. coli) of the B2 phylotype reside in human and animal intestines. The bacteria possess pathogenicity factors such as α-hemolysin (HlyA) that can induce intestinal epithelial leaks. We addressed the questions which host cell processes were dysregulated by E. coli HlyA that can potentiate intestinal diseases. The colon carcinoma cell line Caco-2 was infected by HlyA⁺ E. coli. Cell polarity regulation was analyzed by live cell imaging for the phosphatidylinositol-4,5-bisphosphate (PIP2) abundance. In Caco-2 monolayers, transepithelial electrical resistance was measured for characterization of barrier function. Cell proliferation and separation were assessed microscopically. Epithelial regulation and cell signaling were analyzed by RNA-Seq and Ingenuity Pathway Analysis (IPA). Our main findings from E. coli HlyA toxinogenicity in the colon carcinoma cell line are that (i) PIP2 at the membrane decrease, (ii) PTEN (phosphatase and tensin homolog) inhibition leads to cell polarity changes, (iii) epithelial leakiness follows these polarity changes by disruption of cell junctions and (iv) epithelial cell detachment increases. HlyA affected pathways, e.g., the PTEN and metastasis signaling, were identified by RNA-Seq bioinformatics calculations in IPA. In conclusion, HlyA affects cell polarity, thereby inducing epithelial barrier dysfunction due to defective tight junctions and focal leak induction as an exemplary mechanism for leaky gut.

Early invasion of the bladder wall by solitary bacteria protects UPEC from antibiotics and neutrophil swarms in an organoid model

Recurrence of uropathogenic Escherichia coli (UPEC) infections has been attributed to reactivation of quiescent intracellular reservoirs (QIRs) in deep layers of the bladder wall. QIRs are thought to arise late during infection following dispersal of bacteria from intracellular bacterial communities (IBCs) in superficial umbrella cells. Here, we track the formation of QIR-like bacteria in a bladder organoid model that recapitulates the stratified uroepithelium within a volume suitable for high-resolution live-cell imaging. Bacteria injected into the organoid lumen enter umbrella-like cells and proliferate to form IBC-like bodies. In parallel, single bacteria penetrate deeper layers of the organoid wall, where they localize within or between uroepithelial cells. These "solitary" bacteria evade killing by antibiotics and neutrophils and are morphologically distinct from bacteria in IBCs. We conclude that bacteria with QIR-like properties may arise at early stages of infection, independent of IBC formation and rupture.

Dynamic persistence of UPEC intracellular bacterial communities in a human bladder-chip model of urinary tract infection

Uropathogenic Escherichia coli (UPEC) proliferate within superficial bladder umbrella cells to form intracellular bacterial communities (IBCs) during early stages of urinary tract infections. However, the dynamic responses of IBCs to host stresses and antibiotic therapy are difficult to assess in situ. We develop a human bladder-chip model wherein umbrella cells and bladder microvascular endothelial cells are co-cultured under flow in urine and nutritive media respectively, and bladder filling and voiding mimicked mechanically by application and release of linear strain. Using time-lapse microscopy, we show that rapid recruitment of neutrophils from the vascular channel to sites of infection leads to swarm and neutrophil extracellular trap formation but does not prevent IBC formation. Subsequently, we tracked bacterial growth dynamics in individual IBCs through two cycles of antibiotic administration interspersed with recovery periods which revealed that the elimination of bacteria within IBCs by the antibiotic was delayed, and in some instances, did not occur at all. During the recovery period, rapid proliferation in a significant fraction of IBCs reseeded new foci of infection through bacterial shedding and host cell exfoliation. These insights reinforce a dynamic role for IBCs as harbors of bacterial persistence, with significant consequences for non-compliance with antibiotic regimens.

Urinary tract infections are one of the most common reasons people need antibiotics. These bacterial infections are typically caused by uropathogenic Escherichia coli (also known as UPEC), which either float freely in the urine and wash away when the bladder empties, or form communities inside cells that the bladder struggles to clear. It is possible that the bacteria living within cells are also more protected from the immune system and antibiotics. But this is hard to study in animal models.

To overcome this, Sharma et al. built a ‘bladder-chip’ which mimics the interface between the blood vessels and the tissue layers of the human bladder. Similar chip devices have also been made for other organs. However, until now, no such model had been developed for the bladder.

On the chip created by Sharma et al. is a layer of bladder cells which sit at the bottom of a channel filled with diluted human urine. These cells were infected with UPEC, and then imaged over time to see how the bacteria moved, interacted with the bladder cells, and aggregated together. Immune cells from human blood were then added to a vascular channel underneath the bladder tissue, which is coated with endothelial cells that normally line blood vessels. The immune cells rapidly crossed the endothelial barrier and entered the bladder tissue, and swarmed around sites of infection. In some instances, they released the contents of their cells to form net-like traps to catch the bacteria. But these traps failed to remove the bacteria living inside bladder cells.

Antibiotics were then added to the urine flowing over the bladder cells as well as the vascular channel, similar to how drugs would be delivered in live human tissue. Sharma et al. discovered that the antibiotics killed bacteria residing in bladder cells slower than bacteria floating freely in the urine. Furthermore, they found that bacteria living in tightly packed communities within bladder cells were more likely to survive treatment and go on to re-infect other parts of the tissue.

Antibiotic resistance is a pressing global challenge, and recurrent urinary tract infections are a significant contributor. The bladder-chip presented here could further our understanding of how these bacterial infections develop in vivo and how good antibiotics are at removing them. This could help researchers identify the best dosing and treatment strategies, as well as provide a platform for rapidly testing new antibiotic drugs and other therapies.

Recurrent Urinary Tract Infection: A Mystery in Search of Better Model Systems

Urinary tract infections (UTIs) are among the most common infectious diseases worldwide but are significantly understudied. Uropathogenic E. coli (UPEC) accounts for a significant proportion of UTI, but a large number of other species can infect the urinary tract, each of which will have unique host-pathogen interactions with the bladder environment. Given the substantial economic burden of UTI and its increasing antibiotic resistance, there is an urgent need to better understand UTI pathophysiology - especially its tendency to relapse and recur. Most models developed to date use murine infection; few human-relevant models exist. Of these, the majority of in vitro UTI models have utilized cells in static culture, but UTI needs to be studied in the context of the unique aspects of the bladder's biophysical environment (e.g., tissue architecture, urine, fluid flow, and stretch). In this review, we summarize the complexities of recurrent UTI, critically assess current infection models and discuss potential improvements. More advanced human cell-based in vitro models have the potential to enable a better understanding of the etiology of UTI disease and to provide a complementary platform alongside animals for drug screening and the search for better treatments.

Advanced 3D Cell Culture Techniques in Micro-Bioreactors, Part II: Systems and Applications

In this second part of our systematic review on the research area of 3D cell culture in micro-bioreactors we give a detailed description of the published work with regard to the existing micro-bioreactor types and their applications, and highlight important results gathered with the respective systems. As an interesting detail, we found that micro-bioreactors have already been used in SARS-CoV research prior to the SARS-CoV2 pandemic. As our literature research revealed a variety of 3D cell culture configurations in the examined bioreactor systems, we defined in review part one “complexity levels” by means of the corresponding 3D cell culture techniques applied in the systems. The definition of the complexity is thereby based on the knowledge that the spatial distribution of cell-extracellular matrix interactions and the spatial distribution of homologous and heterologous cell–cell contacts play an important role in modulating cell functions. Because at least one of these parameters can be assigned to the 3D cell culture techniques discussed in the present review, we structured the studies according to the complexity levels applied in the MBR systems.

Advanced 3D Cell Culture Techniques in Micro-Bioreactors, Part I: A Systematic Analysis of the Literature Published between 2000 and 2020

Bioreactors have proven useful for a vast amount of applications. Besides classical large-scale bioreactors and fermenters for prokaryotic and eukaryotic organisms, micro-bioreactors, as specialized bioreactor systems, have become an invaluable tool for mammalian 3D cell cultures. In this systematic review we analyze the literature in the field of eukaryotic 3D cell culture in micro-bioreactors within the last 20 years. For this, we define complexity levels with regard to the cellular 3D microenvironment concerning cell–matrix-contact, cell–cell-contact and the number of different cell types present at the same time. Moreover, we examine the data with regard to the micro-bioreactor design including mode of cell stimulation/nutrient supply and materials used for the micro-bioreactors, the corresponding 3D cell culture techniques and the related cellular microenvironment, the cell types and in vitro models used. As a data source we used the National Library of Medicine and analyzed the studies published from 2000 to 2020.

α-Hemolysin of uropathogenic E. coli regulates NLRP3 inflammasome activation and mitochondrial dysfunction in THP-1 macrophages

Hemolysin expressing UPEC strains have been associated with severe advanced kidney pathologies, such as cystitis and pyelonephritis, which are associated with an inflammatory response. Macrophages play an important role in regulating an inflammatory response during a urinary tract infection. We have studied the role of purified recombinant α-hemolysin in inducing inflammatory responses and cell death in macrophages. Acylation at lysine residues through HlyC is known to activate proHlyA into a fully functional pore-forming toxin, HlyA. It was observed that active α-hemolysin (HlyA) induced cleavage of caspase-1 leading to the maturation of IL-1β, while inactive α-hemolysin (proHlyA) failed to do so in THP-1 derived macrophages. HlyA also promotes deubiquitination, oligomerization, and activation of the NLRP3 inflammasome, which was found to be dependent on potassium efflux. We have also observed the co-localization of NLRP3 within mitochondria during HlyA stimulations. Moreover, blocking of potassium efflux improved the mitochondrial health in addition to a decreased inflammatory response. Our study demonstrates that HlyA stimulation caused perturbance in potassium homeostasis, which led to the mitochondrial dysfunction followed by an acute inflammatory response, resulting in cell death. However, the repletion of intracellular potassium stores could avoid HlyA induced macrophage cell death. The findings of this study will help to understand the mechanism of α-hemolysin induced inflammatory response and cell death.

Current and innovative approaches in the treatment of non-muscle invasive bladder cancer: the role of transurethral resection of bladder tumor and organoids

Background Bladder cancer is the 7th most common cancer in men. About 75% of all bladder cancer are non-muscle invasive (NMIBC). The golden standard for definite diagnosis and first-line treatment of NMIBC is transurethral resection of bladder tumour (TURB). Historically, the monopolar current was used first, today bipolar current is preferred by most urologists. Following TURB, depending on the tumour grade, additional intravesical chemo- or/and immunotherapy is indicated, in order to prevent recurrence and need for surgical resection. Development of new technologies, molecular and cell biology, enabled scientists to develop organoids - systems of human cells that are cultivated in the laboratory and have characteristics of the tissue from which they were harvested. In the field of urologic cancers, the organoids are used mainly for studying the course of different diseases, however, in the field of bladder cancer the data are scarce. Conclusions Different currents - monopolar and bipolar, have different effect on urothelium, that is important for oncological results and pathohistological interpretation. Specimens of bladder cancer can be used for preparation of organoids that are further used for studying carcinogenesis. Bladder organoids are step towards personalised medicine, especially for testing effectiveness of chemo-/immunotherapeutics.

Complex Multilevel Control of Hemolysin Production by Uropathogenic Escherichia coli

Uropathogenic E. coli (UPEC) is the major cause of urinary tract infections and a frequent cause of sepsis. Nearly half of all UPEC strains produce the potent cytotoxin hemolysin, and its expression is associated with enhanced virulence. In this study, we explored hemolysin variation within the globally dominant UPEC ST131 clone, finding that strains from the ST131 sublineage with the greatest multidrug resistance also possess the strongest hemolytic activity. We also employed an innovative forward genetic screen to define the set of genes required for hemolysin production. Using this approach, and subsequent targeted mutagenesis and complementation, we identified new hemolysin-controlling elements involved in LPS inner core biosynthesis and cytoplasmic chaperone activity, and we show that mechanistically they are required for hemolysin secretion. These original discoveries substantially enhance our understanding of hemolysin regulation, secretion and function.

Uropathogenic Escherichia coli (UPEC) is the major cause of urinary tract infections. Nearly half of all UPEC strains secrete hemolysin, a cytotoxic pore-forming toxin. Here, we show that the prevalence of the hemolysin toxin gene (hlyA) is highly variable among the most common 83 E. coli sequence types (STs) represented on the EnteroBase genome database. To explore this diversity in the context of a defined monophyletic lineage, we contextualized sequence variation of the hlyCABD operon within the genealogy of the globally disseminated multidrug-resistant ST131 clone. We show that sequence changes in hlyCABD and its newly defined 1.616-kb-long leader sequence correspond to phylogenetic designation, and that ST131 strains with the strongest hemolytic activity belong to the most extensive multidrug-resistant sublineage (clade C2). To define the set of genes involved in hemolysin production, the clade C2 strain S65EC was completely sequenced and subjected to a genome-wide screen by combining saturated transposon mutagenesis and transposon-directed insertion site sequencing with the capacity to lyse red blood cells. Using this approach, and subsequent targeted mutagenesis and complementation, 13 genes were confirmed to be specifically required for production of active hemolysin. New hemolysin-controlling elements included discrete sets of genes involved in lipopolysaccharide (LPS) inner core biosynthesis (waaC, waaF, waaG, and rfaE) and cytoplasmic chaperone activity (dnaK and dnaJ), and we show these are required for hemolysin secretion. Overall, this work provides a unique description of hemolysin sequence diversity in a single clonal lineage and describes a complex multilevel system of regulatory control for this important toxin.

Variation in hemolysin A expression between uropathogenic Escherichia coli isolates determines NLRP3-dependent vs. -independent macrophage cell death and host colonization

Uropathogenic Escherichia coli (UPEC) is the major cause of urinary tract infections (UTIs). The multidrug-resistant E. coli sequence type 131 (ST131) clone is a serious threat to human health, yet its effects on immune responses are not well understood. Here we screened a panel of ST131 isolates, finding that only strains expressing the toxin hemolysin A (HlyA) killed primary human macrophages and triggered maturation of the inflammasome-dependent cytokine IL-1β. Using a representative strain, the requirement for the hlyA gene in these responses was confirmed. We also observed considerable heterogeneity in levels of cell death initiated by different HlyA^+ve ST131 isolates, and this correlated with secreted HlyA levels. Investigation into the biological significance of this variation revealed that an ST131 strain producing low levels of HlyA initiated cell death that was partly dependent on the nod-like receptor family pyrin domain-containing 3 (NLRP3) inflammasome, with this response being associated with a host-protective role in a mouse UTI model. When the same ST131 strain was engineered to overexpress high HlyA levels, macrophage cell death occurred even when NLRP3 function was abrogated, and bladder colonization was significantly increased. Thus, variation in HlyA expression in UPEC affects mechanisms by which macrophages die, as well as host susceptibility vs. resistance to colonization.-Murthy, A. M. V., Sullivan, M. J., Nhu, N. T. K., Lo, A. W., Phan, M.-D., Peters, K. M., Boucher, D., Schroder, K., Beatson, S. A., Ulett, G. C., Schembri, M. A., Sweet, M. J. Variation in hemolysin A expression between uropathogenic Escherichia coli isolates determines NLRP3-dependent vs. -independent macrophage cell death and host colonization.

Modeling Host-Pathogen Interactions in the Context of the Microenvironment: Three-Dimensional Cell Culture Comes of Age

Tissues and organs provide the structural and biochemical landscapes upon which microbial pathogens and commensals function to regulate health and disease. While flat two-dimensional (2-D) monolayers composed of a single cell type have provided important insight into understanding host-pathogen interactions and infectious disease mechanisms, these reductionist models lack many essential features present in the native host microenvironment that are known to regulate infection, including three-dimensional (3-D) architecture, multicellular complexity, commensal microbiota, gas exchange and nutrient gradients, and physiologically relevant biomechanical forces (e.g., fluid shear, stretch, compression). A major challenge in tissue engineering for infectious disease research is recreating this dynamic 3-D microenvironment (biological, chemical, and physical/mechanical) to more accurately model the initiation and progression of host-pathogen interactions in the laboratory. Here we review selected 3-D models of human intestinal mucosa, which represent a major portal of entry for infectious pathogens and an important niche for commensal microbiota. We highlight seminal studies that have used these models to interrogate host-pathogen interactions and infectious disease mechanisms, and we present this literature in the appropriate historical context. Models discussed include 3-D organotypic cultures engineered in the rotating wall vessel (RWV) bioreactor, extracellular matrix (ECM)-embedded/organoid models, and organ-on-a-chip (OAC) models. Collectively, these technologies provide a more physiologically relevant and predictive framework for investigating infectious disease mechanisms and antimicrobial therapies at the intersection of the host, microbe, and their local microenvironments.

Regulation of hemolysin in uropathogenic Escherichia coli fine-tunes killing of human macrophages

Uropathogenic E. coli (UPEC) causes the majority of urinary tract infections (UTIs), which are a major global public health concern. UPEC uses numerous mechanisms to subvert the innate immune system, including targeting macrophage functions. We recently showed that some UPEC strains rapidly kill human macrophages via an NLRP3-independent pathway, and also trigger NLRP3-dependent IL-1β processing. In this study, we used random transposon mutagenesis in the reference strain CFT073 to identify UPEC genes that mediate human macrophage cell death. Our approach revealed that the hemolysin A (HlyA) toxin is essential for triggering both cell death and NLRP3 inflammasome-mediated IL-1β release in human macrophages. Random transposon mutagenesis also identified the cof gene, which encodes a poorly characterized phosphatase, as a novel hemolysin regulator; a CFT073 mutant deleted for the cof gene secreted significantly reduced levels of HlyA, had diminished hemolytic activity, and was impaired in its capacity to trigger human macrophage cell death and IL-1β release. Together, our findings reveal that Cof fine-tunes production of hemolysin, an important determinant of both UPEC-mediated inflammasome activation and human macrophage cell death.

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.

The potential of organoids in urological cancer research

Technical advances in the development of organoid systems enable cell lines, primary adult cells, or stem or progenitor cells to develop into diverse, multicellular entities, which can self-renew, self-organize, and differentiate. These 3D organoid cultures have proven to be of value in increasing our understanding of the biology of disease and offer the potential of regenerative and genetic therapies. The successful application of 3D organoids derived from adult tissue into urological cancer research can further our understanding of these diseases and could also provide preclinical cancer models to realize the precision medicine paradigm by therapeutic screening of individual patient samples ex vivo. Kidney organoids derived from induced pluripotent stem cells provide personalized biomarkers, which can be correlated with genetic and clinical information. Organoid models can also improve our comprehension of aspects of particular diseases; for example, in prostate cancer, 3D organoids can aid in the identification of tumour-initiating cells from an epithelial cell lineage. Furthermore, kidney organoid differentiation from human pluripotent stem cells enables gene editing to model disease in kidney tubular epithelial cells. State-of-the-art human organoid cultures have potential as tools in basic and clinical research in renal, bladder, and prostatic diseases.

Immunomodulation in the canine endometrium by uteropathogenic Escherichia coli

This study was designed to evaluate the role of E. coli α-hemolysin (HlyA) in the pathogenesis of canine pyometra, and on the immune response of canine endometrial epithelial and stromal cells. In Experiment 1, the clinical, hematological, biochemical and uterine histological characteristics of β-hemolytic and non-hemolytic E. coli pyometra bitches were compared. More (p < 0.05) metritis cases were observed in β-hemolytic E. coli pyometra uteri than in non-hemolytic E. coli pyometra uteri. β-hemolytic E. coli pyometra endometria had higher gene transcription of IL-1β and IL-8 and lower gene transcription of IL-6 than non-hemolytic E. coli pyometra endometria (p < 0.01). In Experiment 2, the immune response of endometrial epithelial and stromal cells, to hemolytic (Pyo18) and non-hemolytic E. coli strains (Pyo18 with deleted hlya-Pyo18ΔhlyA- and Pyo14) were compared. Following 4 h of incubation, Pyo18 decreased epithelial cell numbers to 54% (p < 0.001), and induced death of all stromal cells (p < 0.0001), whereas Pyo18ΔhlyA and Pyo14 had no effect on cell numbers. Compared to Pyo18ΔhlyA and Pyo14, respectively, Pyo18 induced a lower transcription level of IL-1β (0.99 vs 152.0 vs 50.9 fold increase, p < 0.001), TNFα (3.2 vs 49.9 vs 12.9 fold increase, p < 0.05) and IL-10 (0.4 vs 3.6 vs 2.6 fold increase, p < 0.001) in stromal cells, after 1 h of incubation. This may be seen as an attempt of hemolytic E. coli to delay the activation of the immune response. In conclusion, endometrial epithelial and stromal cell damage induced by HlyA is a potential relevant step of E. coli virulence in the pathogenesis of pyometra.

Microgravity as a biological tool to examine host-pathogen interactions and to guide development of therapeutics and preventatives that target pathogenic bacteria

Space exploration programs have long been interested in the effects of spaceflight on biology. This research is important not only in its relevance to future deep space exploration, but also because it has allowed investigators to ask questions about how gravity impacts cell behavior here on Earth. In the 1980s, scientists designed and built the first rotating wall vessel, capable of mimicking the low shear environment found in space. This vessel has since been used to investigate growth of both microorganisms and human tissue cells in low shear modeled microgravity conditions. Bacterial behavior has been shown to be altered both in space and under simulated microgravity conditions. In some cases, bacteria appear attenuated, whereas in others virulence is enhanced. This has consequences not only for manned spaceflight, but poses larger questions about the ability of bacteria to sense the world around them. By using the microgravity environment as a tool, we can exploit this phenomenon in the search for new therapeutics and preventatives against pathogenic bacteria for use both in space and on Earth.

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.

Hemolysin of uropathogenic Escherichia coli: A cloak or a dagger?

Hemolysin from uropathogenic Escherichia coli (UPEC) is a hemolytic and cytotoxic protein active against a broad range of species and cell types. Expression of hemolysin correlates with severity of infection, as up to 78% of UPEC isolates from pyelonephritis cases express hemolysin. Despite decades of research on hemolysin activity, the mechanism of intoxication and the function of hemolysin in UPEC infection remain elusive. Early in vitro research established the role of hemolysin as a lytic protein at high doses. It is hypothesized that hemolysin is secreted at sublytic doses in vivo and recent research has focused on understanding the more subtle effects of hemolysin both in vitro and in elegant infection models in vivo, including inoculation by micropuncture of individual kidney nephrons. As the field continues to evolve, comparisons of hemolysin function in isolates from a range of UTI infections will be important for delineating the role of this toxin. This article is part of a Special Issue entitled: Pore-Forming Toxins edited by Mauro Dalla Serra and Franco Gambale.

Engineered in vitro disease models

The ultimate goal of most biomedical research is to gain greater insight into mechanisms of human disease or to develop new and improved therapies or diagnostics. Although great advances have been made in terms of developing disease models in animals, such as transgenic mice, many of these models fail to faithfully recapitulate the human condition. In addition, it is difficult to identify critical cellular and molecular contributors to disease or to vary them independently in whole-animal models. This challenge has attracted the interest of engineers, who have begun to collaborate with biologists to leverage recent advances in tissue engineering and microfabrication to develop novel in vitro models of disease. As these models are synthetic systems, specific molecular factors and individual cell types, including parenchymal cells, vascular cells, and immune cells, can be varied independently while simultaneously measuring system-level responses in real time. In this article, we provide some examples of these efforts, including engineered models of diseases of the heart, lung, intestine, liver, kidney, cartilage, skin and vascular, endocrine, musculoskeletal, and nervous systems, as well as models of infectious diseases and cancer. We also describe how engineered in vitro models can be combined with human inducible pluripotent stem cells to enable new insights into a broad variety of disease mechanisms, as well as provide a test bed for screening new therapies.

Liver-Tumor Hybrid Organoids for Modeling Tumor Growth and Drug Response In Vitro

Current in vitro models for tumor growth and metastasis are poor facsimiles of in vivo cancer physiology and thus, are not optimal for anti-cancer drug development. Three dimensional (3D) tissue organoid systems, which utilize human cells in a tailored microenvironment, have the potential to recapitulate in vivo conditions and address the drawbacks of current tissue culture dish 2D models. In this study, we created liver-based cell organoids in a rotating wall vessel bioreactor. The organoids were further inoculated with colon carcinoma cells in order to create liver-tumor organoids for in vitro modeling of liver metastasis. Immunofluorescent staining revealed notable phenotypic differences between tumor cells in 2D and inside the organoids. In 2D they displayed an epithelial phenotype, and only after transition to the organoids did the cells present with a mesenchymal phenotype. The cell surface marker expression results suggested that WNT pathway might be involved in the phenotypic changes observed between cells in 2D and organoid conditions, and may lead to changes in cell proliferation. Manipulating the WNT pathway with an agonist and antagonist showed significant changes in sensitivity to the anti-proliferative drug 5-fluoruracil. Collectively, the results show the potential of in vitro 3D liver-tumor organoids to serve as a model for metastasis growth and for testing the response of tumor cells to current and newly discovered drugs.

Antibodies against hemolysin and cytotoxic necrotizing factor type 1 (CNF1) reduce bladder inflammation in a mouse model of urinary tract infection with toxigenic uropathogenic Escherichia coli

Uropathogenic Escherichia coli (UPEC) is the leading cause of cystitis. Cytotoxic necrotizing factor 1 (CNF1) and hemolysin (Hly) are toxins made by approximately 50% of UPEC isolates. CNF1 and Hly contribute to the robust inflammatory response in the bladders of mice challenged with UPEC strain CP9. We hypothesized that antibodies against CNF1 and/or Hly would reduce cystitis caused by CP9. To test this theory, we immunized female C3H/HeOuJ mice subcutaneously with a genetically derived Hly toxoid or genetically derived CNF1 toxoid plus sublethal doses of CNF1. We collected serum and observed increasing titers of specific and neutralizing antibodies against Hly or CNF1 over time. We challenged the mice intraurethrally with CP9 and euthanized them 24 h later. We observed 10-fold lower bacterial titers in the urine of Hly-immunized mice than in that of sham-immunized mice but no difference in kidney bacterial titers. Immunized mice also exhibited significantly less cystitis than sham-immunized mice. In CNF1-vaccinated mice, we detected neither a difference in urine or kidney bacterial titers nor a reduction in the severity of cystitis versus that of sham-immunized mice. We then passively administered an anti-CNF1 monoclonal antibody intraperitoneally to female C3H/HeOuJ mice prior to intraurethral challenge with CP9. Upon challenge, we noted no difference in colonization of the urine or kidney; however, cystitis was reduced significantly in mice treated with the anti-CNF1 antibody versus that in the bladders of mice given an isotype control antibody. Taken together, our data demonstrate that antibodies against CNF1 or Hly reduce the bladder pathology caused by UPEC.

Dysregulation of Escherichia coli α-hemolysin expression alters the course of acute and persistent urinary tract infection

Urinary tract infections (UTIs) are among the most common bacterial infections, causing considerable morbidity in females. Infection is highly recurrent despite appropriate antibiotic treatment. Uropathogenic Escherichia coli (UPEC), the most common causative agent of UTIs, invades bladder epithelial cells (BECs) and develops into clonal intracellular bacterial communities (IBCs). Upon maturation, IBCs disperse, with bacteria spreading to neighboring BECs to repeat this cycle. This process allows UPEC to gain a foothold in the face of innate defense mechanisms, including micturition, epithelial exfoliation, and the influx of polymorphonuclear leukocytes. Here, we investigated the mechanism and dynamics of urothelial exfoliation in the early acute stages of infection. We show that UPEC α-hemolysin (HlyA) induces Caspase-1/Caspase-4-dependent inflammatory cell death in human urothelial cells, and we demonstrate that the response regulator (CpxR)-sensor kinase (CpxA) two-component system (CpxRA), which regulates virulence gene expression in response to environmental signals, is critical for fine-tuning HlyA cytotoxicity. Deletion of the cpxR transcriptional response regulator derepresses hlyA expression, leading to enhanced Caspase-1/Caspase-4- and NOD-like receptor family, pyrin domain containing 3-dependent inflammatory cell death in human urothelial cells. In vivo, overexpression of HlyA during acute bladder infection induces more rapid and extensive exfoliation and reduced bladder bacterial burdens. Bladder fitness is restored fully by inhibition of Caspase-1 and Caspase-11, the murine homolog of Caspase-4. Thus, we have discovered that fine-tuning of HlyA expression by the CpxRA system is critical for enhancing UPEC fitness in the urinary bladder. These results have significant implications for our understanding of how UPEC establishes persistent colonization.

Virulence factors of uropathogenic E. coli and their interaction with the host

Urinary tract infections (UTIs) belong to the most common infectious diseases worldwide. The most frequently isolated pathogen from uncomplicated UTIs is Escherichia coli. To establish infection in the urinary tract, E. coli has to overcome several defence strategies of the host, including the urine flow, exfoliation of urothelial cells, endogenous antimicrobial factors and invading neutrophils. Thus, uropathogenic E. coli (UPEC) harbour a number of virulence and fitness factors enabling the bacterium to resist and overcome these different defence mechanisms. There is no particular factor which allows the identification of UPEC among the commensal faecal flora apart from the ability to enter the urinary tract and cause an infection. Many of potential virulence or fitness factors occur moreover with high redundancy. Fimbriae are inevitable for adherence to and invasion into the host cells; the type 1 pilus is an established virulence factor in UPEC and indispensable for successful infection of the urinary tract. Flagella and toxins promote bacterial dissemination, while different iron-acquisition systems allow bacterial survival in the iron-limited environment of the urinary tract. The immune response to UPEC is primarily mediated by toll-like receptors recognising lipopolysaccharide, flagella and other structures on the bacterial surface. UPEC have the capacity to subvert this immune response of the host by means of actively impacting on pro-inflammatory signalling pathways, or by physical masking of immunogenic structures. The large repertoire of bacterial virulence and fitness factors in combination with host-related differences results in a complex interaction between host and pathogen in the urinary tract.

Critical analysis of 3-D organoid in vitro cell culture models for high-throughput drug candidate toxicity assessments

Drug failure due to toxicity indicators remains among the primary reasons for staggering drug attrition rates during clinical studies and post-marketing surveillance. Broader validation and use of next-generation 3-D improved cell culture models are expected to improve predictive power and effectiveness of drug toxicological predictions. However, after decades of promising research significant gaps remain in our collective ability to extract quality human toxicity information from in vitro data using 3-D cell and tissue models. Issues, challenges and future directions for the field to improve drug assay predictive power and reliability of 3-D models are reviewed.

Virulence factors and o-serogroups profiles of uropathogenic Escherichia coli isolated from Iranian pediatric patients

Background:

Uropathogenic Escherichia coli O- Serogroups with their virulence factors are the most prevalent causes of UTIs.

Objectives:

The present investigation was performed to study the virulence factors and O-Serogroups profiles of UPEC isolated from Iranian pediatric patients.

Patients and Methods:

This cross sectional investigation was performed on 100 urine samples collected from hospitalized pediatrics of Baqiyatallah Hospital, Tehran, Iran. Midstream urine was collected to decrease potential bacterial, cellular and artifactual contamination. All samples were cultured and those with positive results were subjected to polymerase chain reactions to detect pap, cnf1, afa, sfa and hlyA genes and various O- Serogroups.

Results:

We found that 37.5% of boys and 75% of girls had positive results for Escherichia coli. We also found that O1 (19.33%), O2 (13.33%), O6 (13.33%), O4 (11.66%), and O18 (11.66 %) were the most commonly detected Serogroups. Totally, the serogroup of 5% of all strains were not detected. In addition, all of these O- Serogroups were pap+, cnf1+, hlyA+, and afa+. Totally, pap (70 %), cnf1 (56.66 %), and hlyA (43.33 %) were the most commonly detected virulence genes in the both studied groups of children. The sfa (30 %) and afa (26.66 %) genes had the lowest incidence rates.

Conclusions:

Special health care should be performed on UTIs management in Iranian pediatric patients. Extended researches should be performed to evaluate relation between other O-Serogroups and virulent genes.

Human bladder uroepithelial cells synergize with monocytes to promote IL-10 synthesis and other cytokine responses to uropathogenic Escherichia coli

Urinary tract infections are a major source of morbidity for women and the elderly, with Uropathogenic Escherichia coli (UPEC) being the most prevalent causative pathogen. Studies in recent years have defined a key anti-inflammatory role for Interleukin-10 (IL-10) in urinary tract infection mediated by UPEC and other uropathogens. We investigated the nature of the IL-10-producing interactions between UPEC and host cells by utilising a novel co-culture model that incorporated lymphocytes, mononuclear and uroepithelial cells in histotypic proportions. This co-culture model demonstrated synergistic IL-10 production effects between monocytes and uroepithelial cells following infection with UPEC. Membrane inserts were used to separate the monocyte and uroepithelial cell types during infection and revealed two synergistic IL-10 production effects based on contact-dependent and soluble interactions. Analysis of a comprehensive set of immunologically relevant biomarkers in monocyte-uroepithelial cell co-cultures highlighted that multiple cytokine, chemokine and signalling factors were also produced in a synergistic or antagonistic fashion. These results demonstrate that IL-10 responses to UPEC occur via multiple interactions between several cells types, implying a complex role for infection-related IL-10 during UTI. Development and application of the co-culture model described in this study is thus useful to define the degree of contact dependency of biomarker production to UPEC, and highlights the relevance of histotypic co-cultures in studying complex host-pathogen interactions.

From in vitro to in vivo Models of Bacterial Biofilm-Related Infections

The influence of microorganisms growing as sessile communities in a large number of human infections has been extensively studied and recognized for 30–40 years, therefore warranting intense scientific and medical research. Nonetheless, mimicking the biofilm-life style of bacteria and biofilm-related infections has been an arduous task. Models used to study biofilms range from simple in vitro to complex in vivo models of tissues or device-related infections. These different models have progressively contributed to the current knowledge of biofilm physiology within the host context. While far from a complete understanding of the multiple elements controlling the dynamic interactions between the host and biofilms, we are nowadays witnessing the emergence of promising preventive or curative strategies to fight biofilm-related infections. This review undertakes a comprehensive analysis of the literature from a historic perspective commenting on the contribution of the different models and discussing future venues and new approaches that can be merged with more traditional techniques in order to model biofilm-infections and efficiently fight them.

Cytotoxic necrotizing factor 1 and hemolysin from uropathogenic Escherichia coli elicit different host responses in the murine bladder

Cytotoxic necrotizing factor 1 (CNF1) and hemolysin (HlyA1) are toxins produced by uropathogenic Escherichia coli (UPEC). We previously showed that these toxins contribute to the inflammation and tissue damage seen in a mouse model of ascending urinary tract infection. CNF1 constitutively activates small Rho GTPases by deamidation of a conserved glutamine residue, and HlyA1 forms pores in eukaryotic cell membranes. In this study, we used cDNA microarrays of bladder tissue isolated from mice infected intraurethrally with wild-type CP9, CP9cnf1, or CP9ΔhlyA to further evaluate the role that each toxin plays in the host response to UPEC. Regardless of the strain used, we found that UPEC itself elicited a significant change in host gene expression 24 h after inoculation. The largest numbers of upregulated genes were in the cytokine and chemokine signaling and Toll-like receptor signaling pathways. CNF1 exerted a strong positive influence on expression of genes involved in innate immunity and signal transduction and a negative impact on metabolism- and transport-associated genes. HlyA1 evoked an increase in expression of genes that encode innate immunity factors and a decrease in expression of genes involved in cytoskeletal and metabolic processes. Multiplex cytokine and myeloperoxidase assays corroborated our finding that a strong proinflammatory response was elicited by all strains tested. Bladders challenged intraurethrally with purified CNF1 displayed pathology similar to but significantly less intense than the pathology that we observed in CP9-challenged mice. Our data demonstrate substantial roles for CNF1 and HlyA1 in initiation of a strong proinflammatory response to UPEC in the bladder.

The UPEC pore-forming toxin α-hemolysin triggers proteolysis of host proteins to disrupt cell adhesion, inflammatory, and survival pathways

Uropathogenic Escherichia coli (UPEC), which are the leading cause of both acute and chronic urinary tract infections, often secrete a labile pore-forming toxin known as α-hemolysin (HlyA). We show that stable insertion of HlyA into epithelial cell and macrophage membranes triggers degradation of the cytoskeletal scaffolding protein paxillin and other host regulatory proteins, as well as components of the proinflammatory NFκB signaling cascade. Proteolysis of these factors requires host serine proteases, and paxillin degradation specifically involves the serine protease mesotrypsin. The induced activation of mesotrypsin by HlyA is preceded by redistribution of mesotrypsin precursors from the cytosol into foci along microtubules and within nuclei. HlyA intoxication also stimulated caspase activation, which occurred independently of effects on host serine proteases. HlyA-induced proteolysis of host proteins likely allows UPEC to not only modulate epithelial cell functions, but also disable macrophages and suppress inflammatory responses.

Culturing and applications of rotating wall vessel bioreactor derived 3D epithelial cell models

Cells and tissues in the body experience environmental conditions that influence their architecture, intercellular communications, and overall functions. For in vitro cell culture models to accurately mimic the tissue of interest, the growth environment of the culture is a critical aspect to consider. Commonly used conventional cell culture systems propagate epithelial cells on flat two-dimensional (2-D) impermeable surfaces. Although much has been learned from conventional cell culture systems, many findings are not reproducible in human clinical trials or tissue explants, potentially as a result of the lack of a physiologically relevant microenvironment. Here, we describe a culture system that overcomes many of the culture condition boundaries of 2-D cell cultures, by using the innovative rotating wall vessel (RWV) bioreactor technology. We and others have shown that organotypic RWV-derived models can recapitulate structure, function, and authentic human responses to external stimuli similarly to human explant tissues (1-6). The RWV bioreactor is a suspension culture system that allows for the growth of epithelial cells under low physiological fluid shear conditions. The bioreactors come in two different formats, a high-aspect rotating vessel (HARV) or a slow-turning lateral vessel (STLV), in which they differ by their aeration source. Epithelial cells are added to the bioreactor of choice in combination with porous, collagen-coated microcarrier beads (Figure 1A). The cells utilize the beads as a growth scaffold during the constant free fall in the bioreactor (Figure 1B). The microenvironment provided by the bioreactor allows the cells to form three-dimensional (3-D) aggregates displaying in vivo-like characteristics often not observed under standard 2-D culture conditions (Figure 1D). These characteristics include tight junctions, mucus production, apical/basal orientation, in vivo protein localization, and additional epithelial cell-type specific properties. The progression from a monolayer of epithelial cells to a fully differentiated 3-D aggregate varies based on cell type(1, 7-13). Periodic sampling from the bioreactor allows for monitoring of epithelial aggregate formation, cellular differentiation markers and viability (Figure 1D). Once cellular differentiation and aggregate formation is established, the cells are harvested from the bioreactor, and similar assays performed on 2-D cells can be applied to the 3-D aggregates with a few considerations (Figure 1E-G). In this work, we describe detailed steps of how to culture 3-D epithelial cell aggregates in the RWV bioreactor system and a variety of potential assays and analyses that can be executed with the 3-D aggregates. These analyses include, but are not limited to, structural/morphological analysis (confocal, scanning and transmission electron microscopy), cytokine/chemokine secretion and cell signaling (cytometric bead array and Western blot analysis), gene expression analysis (real-time PCR), toxicological/drug analysis and host-pathogen interactions. The utilization of these assays set the foundation for more in-depth and expansive studies such as metabolomics, transcriptomics, proteomics and other array-based applications. Our goal is to present a non-conventional means of culturing human epithelial cells to produce organotypic 3-D models that recapitulate the human in vivo tissue, in a facile and robust system to be used by researchers with diverse scientific interests.

Role of Uropathogenic Escherichia coli Virulence Factors in Development of Urinary Tract Infection and Kidney Damage

Uropathogenic Escherichia coli (UPEC) is a causative agent in the vast majority of urinary tract infections (UTIs), including cystitis and pyelonephritis, and infectious complications, which may result in acute renal failure in healthy individuals as well as in renal transplant patients. UPEC expresses a multitude of virulence factors to break the inertia of the mucosal barrier. In response to the breach by UPEC into the normally sterile urinary tract, host inflammatory responses are triggered leading to cytokine production, neutrophil influx, and the exfoliation of infected bladder epithelial cells. Several signaling pathways activated during UPEC infection, including the pathways known to activate the innate immune response, interact with calcium-dependent signaling pathways. Some UPEC isolates, however, might possess strategies to delay or suppress the activation of components of the innate host response in the urinary tract. Studies published in the recent past provide new information regarding how virulence factors of uropathogenic E. coli are involved in activation of the innate host response. Despite numerous host defense mechanisms, UPEC can persist within the urinary tract and may serve as a reservoir for recurrent infections and serious complications. Presentation of the molecular details of these events is essential for development of successful strategies for prevention of human UTIs and urological complications associated with UTIs.

Epithelial cell coculture models for studying infectious diseases: benefits and limitations

Countless in vitro cell culture models based on the use of epithelial cell types of single lineages have been characterized and have provided insight into the mechanisms of infection for various microbial pathogens. Diverse culture models based on disease-relevant mucosal epithelial cell types derived from gastrointestinal, genitourinary, and pulmonary organ systems have delineated many key host-pathogen interactions that underlie viral, parasitic, and bacterial disease pathogenesis. An alternative to single lineage epithelial cell monoculture, which offers more flexibility and can overcome some of the limitations of epithelial cell culture models based on only single cell types, is coculture of epithelial cells with other host cell types. Various coculture models have been described, which incorporate epithelial cell types in culture combination with a wide range of other cell types including neutrophils, eosinophils, monocytes, and lymphocytes. This paper will summarize current models of epithelial cell coculture and will discuss the benefits and limitations of epithelial cell coculture for studying host-pathogen dynamics in infectious diseases.

Evolution of Cryptosporidium in vitro culture

This overview discusses findings from culturing Cryptosporidium spp. in cell and axenic cultures as well as factors limiting the development of this parasite in cultivation systems during recent years. A systematic review is undertaken of findings regarding the life cycle of the parasite, taking into account physiological, biochemical and genetic aspects, in the hope that this attempt will facilitate future approaches to research and developments in the understanding of Cryptosporidium biology.

Attenuation of human neutrophil migration and function by uropathogenic bacteria

The establishment of bacterial infections at mucosal epithelial surfaces is determined by the balance of virulence attributes of the pathogen with the activity of innate host defenses. Polymorphonuclear leukocytes (PMN) are key responders in many bacterial infections, but the mechanisms by which pathogens subvert these early responses to establish infection are largely undefined. Here, we model early interactions between human PMN and the primary cause of urinary tract infections, namely uropathogenic Escherichia coli (UPEC). Our objective was to define virulence phenotypes of uropathogens that permit evasion of PMN activity. We show that UPEC strains, as compared with laboratory and commensal E. coli, resist phagocytic killing and dampen the production of antimicrobial reactive oxygen species by PMN. Analysis of the transcriptional responses of PMN to E. coli strains revealed that UPEC exposure downregulates the expression of PMN genes that direct pro-inflammatory signaling and PMN chemotaxis, adhesion, and migration. Consistent with these data, UPEC attenuated transepithelial neutrophil recruitment in an in vitro model of acute infection and in a murine model of bacterial cystitis. We propose that these UPEC strategies are important in the establishment of epithelial infection, and that the findings are germane to bacterial infections at other epithelial surfaces.

Organotypic 3D cell culture models: using the rotating wall vessel to study host-pathogen interactions

Appropriately simulating the three-dimensional (3D) environment in which tissues normally develop and function is crucial for engineering in vitro models that can be used for the meaningful dissection of host-pathogen interactions. This Review highlights how the rotating wall vessel bioreactor has been used to establish 3D hierarchical models that range in complexity from a single cell type to multicellular co-culture models that recapitulate the 3D architecture of tissues observed in vivo. The application of these models to the study of infectious diseases is discussed.

Alveolar epithelium protects macrophages from quorum sensing-induced cytotoxicity in a three-dimensional co-culture model

The quorum sensing signal N-(3-oxododecanoyl)-l-homoserine lactone (3-oxo-C(12) HSL), produced by Pseudomonas aeruginosa, exerts cytotoxic effects in macrophages in vitro, which is believed to affect host innate immunity in vivo. However, the medical significance of this finding to pulmonary disease remains unclear since the multicellular complexity of the lung was not considered in the assessment of macrophage responses to 3-oxo-C(12) HSL. We developed a novel three-dimensional co-culture model of alveolar epithelium and macrophages using the rotating wall vessel (RWV) bioreactor, by adding undifferentiated monocytes to RWV-derived alveolar epithelium. Our three-dimensional model expressed important architectural/phenotypic hallmarks of the parental tissue, as evidenced by highly differentiated epithelium, spontaneous differentiation of monocytes to functional macrophage-like cells, localization of these cells on the alveolar surface and a macrophage-to-epithelial cell ratio relevant to the in vivo situation. Co-cultivation of macrophages with alveolar epithelium counteracted 3-oxo-C(12) HSL-induced cytotoxicity via removal of quorum sensing molecules by alveolar cells. Furthermore, 3-oxo-C(12) HSL induced the intercellular adhesion molecule ICAM-1 in both alveolar epithelium and macrophages. These data stress the importance of multicellular organotypic models to integrate the role of different cell types in overall lung homeostasis and disease development in response to external factors.

The generation of 3-D tissue models based on hyaluronan hydrogel-coated microcarriers within a rotating wall vessel bioreactor

With the increasing necessity for functional tissue- and organ equivalents in the clinic, the optimization of techniques for the in vitro generation of organotypic structures that closely resemble the native tissue is of paramount importance. The engineering of a variety of highly differentiated tissues has been achieved using the rotating wall vessel (RWV) bioreactor technology, which is an optimized suspension culture allowing cells to grow in three-dimensions (3-D). However, certain cell types require the use of scaffolds, such as collagen-coated microcarrier beads, for optimal growth and differentiation in the RWV. Removal of the 3-D structures from the microcarriers involves enzymatic treatment, which disrupts the delicate 3-D architecture and makes it inapplicable for potential implantation. Therefore, we designed a microcarrier bead coated with a synthetic extracellular matrix (ECM) composed of a disulfide-crosslinked hyaluronan and gelatin hydrogel for 3-D tissue engineering, that allows for enzyme-free cell detachment under mild reductive conditions (i.e. by a thiol-disulfide exchange reaction). The ECM-coated beads (ECB) served as scaffold to culture human intestinal epithelial cells (Int-407) in the RWV, which formed viable multi-layered cell aggregates and expressed epithelial differentiation markers. The cell aggregates remained viable following dissociation from the microcarriers, and could be returned to the RWV bioreactor for further culturing into bead-free tissue assemblies. The developed ECBs thus offer the potential to generate scaffold-free 3-D tissue assemblies, which could further be explored for tissue replacement and remodeling.

Different responsiveness of endothelial cells to vascular endothelial growth factor and basic fibroblast growth factor added to culture media under gravity and simulated microgravity

When incubated under simulated microgravity (s-microg), endothelial cells (EC) form tubular structures that resemble vascular intimas. This delayed formation of 3D EC structures begins between the 5th and 7th day of culturing EC under conditions of s-microg, when double-row cell assemblies become visible. With the aim of learning about this initial phase of tubular structure formation, we found that NFkappaBp65 protein content was similar in all cell populations, but gene and protein expression of phosphokinase A catalytic subunit, phosphokinase Calpha, and extracellular signal-regulated kinases 1 and 2 was altered in cells cultured under s-microg. Apoptosis remained below 30% in all EC cultures. In contrast to controls, the 7-day-old s-microg cultures contained 3D aggregates with proliferating cells, enhanced numbers of necrotic cells, and osteopontin-negative EC as well as supernatants with reduced quantities of vascular endothelial growth factor (VEGF), basic fibroblast growth factor (bFGF), soluble TNFRSF5, TNFSF5, intercellular adhesion molecule-1, tumor necrosis factor receptor 2, IL-18, complement C3, and von Willebrand factor. VEGF and/or bFGF (10 ng/mL) application influenced the accumulation of proteins in supernatants more profoundly under 1 g than under s-microg. These findings provide evidence that phosphokinase Calpha plays a key role in tube formation. Improving the interaction of VEGF and/or bFGF with EC under s-microg could enhance the engineering of vascular intimas.