Adhesive fiber stratification in uropathogenic Escherichia coli biofilms unveils oxygen-mediated control of type 1 pili

An Overview of Two-Component Signal Transduction Systems Implicated in Extra-Intestinal Pathogenic E. coli Infections

Extra-intestinal pathogenic E. coli (ExPEC) infections are common in mammals and birds. The predominant ExPEC types are avian pathogenic E. coli (APEC), neonatal meningitis causing E. coli/meningitis associated E. coli (NMEC/MAEC), and uropathogenic E. coli (UPEC). Many reviews have described current knowledge on ExPEC infection strategies and virulence factors, especially for UPEC. However, surprisingly little has been reported on the regulatory modules that have been identified as critical in ExPEC pathogenesis. Two-component systems (TCSs) comprise the predominant method by which bacteria respond to changing environments and play significant roles in modulating bacterial fitness in diverse niches. Recent studies have highlighted the potential of manipulating signal transduction systems as a means to chemically re-wire bacterial pathogens, thereby reducing selective pressure and avoiding the emergence of antibiotic resistance. This review begins by providing a brief introduction to characterized infection strategies and common virulence factors among APEC, NMEC, and UPEC and continues with a comprehensive overview of two-component signal transduction networks that have been shown to influence ExPEC pathogenesis.

Identification of a High-Affinity Pyruvate Receptor in Escherichia coli

Two-component systems are crucial for signal perception and modulation of bacterial behavior. Nevertheless, to date, very few ligands have been identified that directly interact with histidine kinases. The histidine kinase/response regulator system YehU/YehT of Escherichia coli is part of a nutrient-sensing network. Here we demonstrate that this system senses the onset of nutrient limitation in amino acid rich media and responds to extracellular pyruvate. Binding of radiolabeled pyruvate was found for full-length YehU in right-side-out membrane vesicles as well as for a truncated, membrane-integrated variant, confirming that YehU is a high-affinity receptor for extracellular pyruvate. Therefore we propose to rename YehU/YehT as BtsS/BtsR, after "Brenztraubensäure", the name given to pyruvic acid when it was first synthesized. The function of BtsS/BtsR was also assessed in a clinically relevant uropathogenic E. coli strain. Quantitative transcriptional analysis revealed BtsS/BtsR importance during acute and chronic urinary-tract infections.

The Significant Influence of Bacterial Reaction on Physico-Chemical Property Changes of Biodegradable Natural and Synthetic Polymers Using Escherichia coli

Escherichia coli (E. coli) was used to activate hydrolysis reaction along with biodegradation in natural and synthetic fibers to identify possibilities as alternative substitutes for textile wastes using chemical solutions and enzymes. To confirm the reaction between the bacterial infections of E. coli and the excessively abundant interstitial spaces of the fibers, various types of natural and synthetic fibers such as cotton, wool, polyethylene terephalate (PET), polyadmide (PA), polyethylene (PE), and polypropylene (PP) were used to confirm the physico-chemical reactions. Tensile strength analysis, scanning electron microscopy (SEM), X-ray photoelectron spectroscopy (XPS), and contact angle analysis were used to determine the physico-chemical property changes of the fiber by the bacteria. When biofilm was formed on the fiber surface, various physical changes such as the following were observed: (i) in the analysis of tensile strength, all except PA and PP were decreased and a decrease in cotton fibers was noticeable (ii) depending on the type of fibers, the degree of roughness was different, but generally the surface became rough. In this study, the change of roughness was the most severe on the cotton fiber surface and the change of PET and PA fiber was relatively small. It was found that the intensity peak of oxygen was increased, except for the in cases of PA and PP, through the change of chemical properties by XPS analysis. Changes in topographical properties on the surface through contact angle analysis were stronger in hydrophilic properties, and in the case of cotton, completely hydrophilic surfaces were formed. Through this study, PA and PP fibers, which are Olefin fibers, were theoretically free of physicochemical and topographical changes since there were no functional groups that could trigger the hydrolysis reaction.

Characterization of blue light irradiation effects on pathogenic and nonpathogenic Escherichia coli

Blue light irradiation (BLI) is an FDA-approved method for treating certain types of infections, like acne, and is becoming increasingly attractive as an antimicrobial strategy as the prevalence of antibiotic-resistant "superbugs" rises. However, no study has delineated the effectiveness of BLI throughout different bacterial growth phases, especially in more BLI-tolerant organisms such as Escherichia coli. While the vast majority of E. coli strains are nonpathogenic, several E. coli pathotypes exist that cause infection within and outside the gastrointestinal tract. Here, we compared the response of E. coli strains from five phylogenetic groups to BLI with a 455 nm wavelength (BLI₄₅₅ ), using colony-forming unit and ATP measurement assays. Our results revealed that BLI₄₅₅ is not bactericidal, but can retard E. coli growth in a manner that is dependent on culture age and strain background. This observation is critical, given that bacteria on and within mammalian hosts are found in different phases of growth.

Blood Serum Affects Polysaccharide Production and Surface Protein Expression in S. Aureus

BACKGROUND

S. aureus biofilm serves a major role in pathogenesis. Two of the major components of bacterial biofilm are Polysaccharides intercellular adhesions (PIA) and surface proteins. It is not known how PIA and surface proteins expressions are affected in presence of blood serum. Analyses of surface proteins expressions will provide more effective biomarker discovery that might lead to development of antimicrobial therapeutics to meet the challenges of biofilm-related infections.

METHOD

Secondary cultures of S. aureus Philips, a biofilm-forming bacterium, were generated by inoculating 1 ml of overnight culture into 50 ml of TSB. Bacteria were cultured at several concentrations of blood serum and found that 12.5% supplemented blood serum provide s similar growth curve as normal TSB (100%). One and 2 D SASPAGE were used to separate proteins and the differentially expressed proteins were identified by nano-LC/MS.

RESULTS

Polysaccharide intercellular adhesions production was significantly increased due to the addition of blood serum in the media. We also identified two serum proteins, apolipoprotein and globulin (Fc and Fab), that remained attached with the membrane fraction of bacterial proteins.

CONCLUSION

These results have strongly demonstrated that blood serum influences the exopolysaccharide expression in S. aureus.

Purine Biosynthesis Metabolically Constrains Intracellular Survival of Uropathogenic Escherichia coli

The ability to de novo synthesize purines has been associated with the intracellular survival of multiple bacterial pathogens. Uropathogenic Escherichia coli (UPEC), the predominant cause of urinary tract infections, undergoes a transient intracellular lifestyle during which bacteria clonally expand into multicellular bacterial communities within the cytoplasm of bladder epithelial cells. Here, we characterized the contribution of the conserved de novo purine biosynthesis-associated locus cvpA-purF to UPEC pathogenesis. Deletion of cvpA-purF, or of purF alone, abolished de novo purine biosynthesis but did not impact bacterial adherence properties in vitro or in the bladder lumen. However, upon internalization by bladder epithelial cells, UPEC deficient in de novo purine biosynthesis was unable to expand into intracytoplasmic bacterial communities over time, unless it was extrachromosomally complemented. These findings indicate that UPEC is deprived of purine nucleotides within the intracellular niche and relies on de novo purine synthesis to meet this metabolic requirement.

Bacterial pili, with emphasis on Mycobacterium tuberculosis curli pili: potential biomarkers for point-of care tests and therapeutics

CONTEXT

Novel biomarkers are essential for developing rapid diagnostics and therapeutic interventions Objective: This review aimed to highlight biomarker characterisation and assessment of unique bacterial pili.

METHODS

A PubMed search for bacterial pili, diagnostics, vaccine and therapeutics was performed, with emphasis on the well characterised pili.

RESULTS

In total, 46 papers were identified and reviewed.

CONCLUSION

Extensive analyses of pili enabled by advanced nanotechnology and whole genome sequencing provide evidence that they are strong biomarker candidates. Mycobacterium tuberculosis curli pili are emphasised as important epitopes for the development of much needed point-of-care diagnostics and therapeutics.

Functional analysis of Escherichia coli Yad fimbriae reveals their potential role in environmental persistence

Initial adhesion of bacterial cells to surfaces or host tissues is a key step in colonisation and biofilm formation processes, and is mediated by cell surface appendages. It was previously demonstrated that Escherichia coli K-12 possesses an arsenal of silenced chaperone-usher fimbriae that were functional when constitutively expressed. Among them, production of prevalent Yad fimbriae induces adhesion to abiotic surfaces. Functional characterisation of Yad fimbriae were undertook, and YadN was identified as the most abundant and potential major pilin, and YadC as the potential tip-protein of Yad fimbriae. It was showed that Yad production participates to binding of E. coli K-12 to human eukaryotic cells (Caco-2) and inhibits macrophage phagocytosis, but also enhances E. coli K-12 binding to xylose, a major component of the plant cell wall, through its tip-lectin YadC. Consistently, it was demonstrated that Yad production provides E. coli with a competitive advantage in colonising corn seed rhizospheres. The latter phenotype is correlated with induction of Yad expression at temperatures below 37°C, and under anaerobic conditions, through a complex regulatory network. Taken together, these results suggest that Yad fimbriae are versatile adhesins that beyond potential capacities to modulate host-pathogen interactions might contribute to E. coli environmental persistence.

The UbiI (VisC) Aerobic Ubiquinone Synthase Is Required for Expression of Type 1 Pili, Biofilm Formation, and Pathogenesis in Uropathogenic Escherichia coli

Uropathogenic Escherichia coli (UPEC), which causes the majority of urinary tract infections (UTI), uses pilus-mediated adherence to initiate biofilm formation in the urinary tract. Oxygen gradients within E. coli biofilms regulate expression and localization of adhesive type 1 pili. A transposon mutant screen for strains defective in biofilm formation identified the ubiI (formerly visC) aerobic ubiquinone synthase gene as critical for UPEC biofilm formation. In this study, we characterized a nonpolar ubiI deletion mutant and compared its behavior to that of wild-type bacteria grown under aerobic and anoxic conditions. Consistent with its function as an aerobic ubiquinone-8 synthase, deletion of ubiI in UPEC resulted in reduced membrane potential, diminished motility, and reduced expression of chaperone-usher pathway pili. Loss of aerobic respiration was previously shown to negatively impact expression of type 1 pili. To determine whether this reduction in type 1 pili was due to an energy deficit, wild-type UPEC and the ubiI mutant were compared for energy-dependent phenotypes under anoxic conditions, in which quinone synthesis is undertaken by anaerobic quinone synthases. Under anoxic conditions, the two strains exhibited wild-type levels of motility but produced diminished numbers of type 1 pili, suggesting that the reduction of type 1 pilus expression in the absence of oxygen is not due to a cellular energy deficit. Acute- and chronic-infection studies in a mouse model of UTI revealed a significant virulence deficit in the ubiI mutant, indicating that UPEC encounters enough oxygen in the bladder to induce aerobic ubiquinone synthesis during infection.

IMPORTANCE

The majority of urinary tract infections are caused by uropathogenic E. coli, a bacterium that can respire in the presence and absence of oxygen. The bladder environment is hypoxic, with oxygen concentrations ranging from 4% to 7%, compared to 21% atmospheric oxygen. This work provides evidence that aerobic ubiquinone synthesis must be engaged during bladder infection, indicating that UPEC bacteria sense and use oxygen as a terminal electron acceptor in the bladder and that this ability drives infection potential despite the fact that UPEC is a facultative anaerobe.

Biofilms 2015: Multidisciplinary Approaches Shed Light into Microbial Life on Surfaces

The 7th ASM Conference on Biofilms was held in Chicago, Illinois, from 24 to 29 October 2015. The conference provided an international forum for biofilm researchers across academic and industry platforms, and from different scientific disciplines, to present and discuss new findings and ideas. The meeting covered a wide range of topics, spanning environmental sciences, applied biology, evolution, ecology, physiology, and molecular biology of the biofilm lifestyle. This report summarizes the presentations with regard to emerging biofilm-related themes.

The innate immune protein calprotectin promotes Pseudomonas aeruginosa and Staphylococcus aureus interaction

Microorganisms form biofilms containing differentiated cell populations. To determine factors driving differentiation, we herein visualize protein and metal distributions within Pseudomonas aeruginosa biofilms using imaging mass spectrometry. These in vitro experiments reveal correlations between differential protein distribution and metal abundance. Notably, zinc- and manganese-depleted portions of the biofilm repress the production of anti-staphylococcal molecules. Exposure to calprotectin (a host protein known to sequester metal ions at infectious foci) recapitulates responses occurring within metal-deplete portions of the biofilm and promotes interaction between P. aeruginosa and Staphylococcus aureus. Consistent with these results, the presence of calprotectin promotes co-colonization of the murine lung, and polymicrobial communities are found to co-exist in calprotectin-enriched airspaces of a cystic fibrosis lung explant. These findings, which demonstrate that metal fluctuations are a driving force of microbial community structure, have clinical implications because of the frequent occurrence of P. aeruginosa and S. aureus co-infections.

Co-infections with Pseudomonas aeruginosa and Staphylococcus aureus are common in cystic fibrosis patients. Here, the authors show that metal depletion induced by a host protein, calprotectin, promotes co-existence of both pathogens by inhibiting production of anti-staphylococcal molecules by P. aeruginosa.

Detecting Bacterial Surface Organelles on Single Cells Using Optical Tweezers

Bacterial cells display a diverse array of surface organelles that are important for a range of processes such as intercellular communication, motility and adhesion leading to biofilm formation, infections, and bacterial spread. More specifically, attachment to host cells by Gram-negative bacteria are mediated by adhesion pili, which are nanometers wide and micrometers long fibrous organelles. Since these pili are significantly thinner than the wavelength of visible light, they cannot be detected using standard light microscopy techniques. At present, there is no fast and simple method available to investigate if a single cell expresses pili while keeping the cell alive for further studies. In this study, we present a method to determine the presence of pili on a single bacterium. The protocol involves imaging the bacterium to measure its size, followed by predicting the fluid drag based on its size using an analytical model, and thereafter oscillating the sample while a single bacterium is trapped by an optical tweezer to measure its effective fluid drag. Comparison between the predicted and the measured fluid drag thereby indicate the presence of pili. Herein, we verify the method using polymer coated silica microspheres and Escherichia coli bacteria expressing adhesion pili. Our protocol can in real time and within seconds assist single cell studies by distinguishing between piliated and nonpiliated bacteria.

Metabolic Requirements of Escherichia coli in Intracellular Bacterial Communities during Urinary Tract Infection Pathogenesis

Uropathogenic Escherichia coli (UPEC) is the primary etiological agent of over 85% of community-acquired urinary tract infections (UTIs). Mouse models of infection have shown that UPEC can invade bladder epithelial cells in a type 1 pilus-dependent mechanism, avoid a TLR4-mediated exocytic process, and escape into the host cell cytoplasm. The internalized UPEC can clonally replicate into biofilm-like intracellular bacterial communities (IBCs) of thousands of bacteria while avoiding many host clearance mechanisms. Importantly, IBCs have been documented in urine from women and children suffering acute UTI. To understand this protected bacterial niche, we elucidated the transcriptional profile of bacteria within IBCs using microarrays. We delineated the upregulation within the IBC of genes involved in iron acquisition, metabolism, and transport. Interestingly, lacZ was highly upregulated, suggesting that bacteria were sensing and/or utilizing a galactoside for metabolism in the IBC. A ΔlacZ strain displayed significantly smaller IBCs than the wild-type strain and was attenuated during competitive infection with a wild-type strain. Similarly, a galK mutant resulted in smaller IBCs and attenuated infection. Further, analysis of the highly upregulated gene yeaR revealed that this gene contributes to oxidative stress resistance and type 1 pilus production. These results suggest that bacteria within the IBC are under oxidative stress and, consistent with previous reports, utilize nonglucose carbon metabolites. Better understanding of the bacterial mechanisms used for IBC development and establishment of infection may give insights into development of novel anti-virulence strategies.

Urinary tract infections (UTIs) are one of the most common bacterial infections, impacting mostly women. Every year, millions of UTIs occur in the U.S. with most being caused by uropathogenic E. coli (UPEC). During a UTI, UPEC invade bladder cells and form an intracellular bacterial community (IBC) that allows for the bacteria to replicate protected from the host immune response. In this study, we investigated genes that are expressed by UPEC within the IBC and determined how they contribute to the formation of this specialized community. Our findings suggest that galactose is important for UPEC growth in the IBC. Additionally, we found that a gene involved in oxidative stress is also important in the regulation of a key factor needed for UPEC invasion of bladder cells. These results may open the door for the development of treatments to diminish UTI frequency and/or severity.

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.

Perspective: Adhesion Mediated Signal Transduction in Bacterial Pathogens

During the infection process, pathogenic bacteria undergo large-scale transcriptional changes to promote virulence and increase intrahost survival. While much of this reprogramming occurs in response to changes in chemical environment, such as nutrient availability and pH, there is increasing evidence that adhesion to host-tissue can also trigger signal transduction pathways resulting in differential gene expression. Determining the molecular mechanisms of adhesion-mediated signaling requires disentangling the contributions of chemical and mechanical stimuli. Here we highlight recent work demonstrating that surface attachment drives a transcriptional response in bacterial pathogens, including uropathogenic Escherichia coli (E. coli), and discuss the complexity of experimental design when dissecting the specific role of adhesion-mediated signaling during infection.

The Challenging World of Biofilm Physiology

Worldwide, infectious diseases are one of the leading causes of death among children. At least 65% of all infections are caused by the biofilm mode of bacterial growth. Bacteria colonise surfaces and grow as multicellular biofilm communities surrounded by a polymeric matrix as a common survival strategy. These sessile communities endow bacteria with high tolerance to antimicrobial agents and hence cause persistent and chronic bacterial infections, such as dental caries, periodontitis, otitis media, cystic fibrosis and pneumonia. The highly complex nature and the rapid adaptability of the biofilm population impede our understanding of the process of biofilm formation, but an important role for oxygen-binding proteins herein is clear. Much research on this bacterial lifestyle is already performed, from genome/proteome analysis to in vivo antibiotic susceptibility testing, but without significant progress in biofilm treatment or eradication. This review will present the multiple challenges of biofilm research and discuss possibilities to cross these barriers in future experimental studies.

The yin-yang driving urinary tract infection and how proteomics can enhance research, diagnostics, and treatment

Bacterial urinary tract infections (UTIs) afflict millions of people worldwide both in the community and the hospital setting. The onset, duration, and severity of infection depend on the characteristics of the invading pathogen (yin), as well as the immune response elicited by the infected individual (yang). Uropathogenic Escherichia coli (UPEC) account for the majority of UTIs, and extensive investigations by many scientific groups have elucidated an elaborate pathogenic UPEC life cycle, involving the occupation of extracellular and intracellular niches and the expression of an arsenal of virulence factors that facilitate niche occupation. This review will summarize the current knowledge on UPEC pathogenesis; the host immune responses elicited to combat infection; and it will describe proteomics approaches used to understand UPEC pathogenesis, as well as drive diagnostics and treatment options. Finally, new strategies are highlighted that could be applied toward furthering our knowledge regarding host-bacterial interactions during UTI.

Sialic acid and N-acetylglucosamine Regulate type 1 Fimbriae Synthesis

Type 1 fimbriae of E. coli , a chaperon-usher bacterial adhesin, are synthesized by the majority of strains of the bacterium. Although frequently produced by commensal strains, the adhesin is nevertheless a virulence factor in Extraintestinal Pathogenic E. coli (ExPEC). The role of the adhesin in pathogenesis is best understood in Uropathogenic E. coli (UPEC). Host attachment and invasion by type 1 fimbriate bacteria activates inflammatory pathways, with TLR4 signaling playing a predominant role. In a mouse model of cystitis, type 1 fimbriation not only enhances UPEC adherence to the surface of superficial umbrella cells of the bladder urothelium, but is both necessary and sufficient for their invasion. Moreover the adhesin plays a role in the formation of transient intracellular bacterial communities (IBCs) within the cytoplasm of urothelial cells as part of UPEC cycles of invasion. The expression of type 1 fimbriation is controlled by phase variation at the transcriptional level, a mode of gene regulation in which bacteria switch reversibly between fimbriate and afimbriate phases. Phase variation has been widely considered to be a mechanism enabling immune evasion. Notwithstanding the apparently random nature of phase variation, switching of type 1 fimbrial expression is nevertheless controlled by a range of environmental signals that include the amino sugars sialic acid and N-acetylglucosamine (GlcNAc). Sialic acid plays a pivotal role in innate immunity, including signaling by the toll-like receptors. Here how sialic acid and GlcNAc control type 1 fimbriation is described and the potential significance of this regulatory response is discussed.