The bacterial amyloid curli is associated with urinary source bloodstream infection

A convergent evolutionary pathway attenuating cellulose production drives enhanced virulence of some bacteria

Bacteria adapt to selective pressure in their immediate environment in multiple ways. One mechanism involves the acquisition of independent mutations that disable or modify a key pathway, providing a signature of adaptation via convergent evolution. Extra-intestinal pathogenic Escherichia coli (ExPEC) belonging to sequence type 95 (ST95) represent a global clone frequently associated with severe human infections including acute pyelonephritis, sepsis, and neonatal meningitis. Here, we analysed a publicly available dataset of 613 ST95 genomes and identified a series of loss-of-function mutations that disrupt cellulose production or its modification in 55.3% of strains. We show the inability to produce cellulose significantly enhances ST95 invasive infection in a rat model of neonatal meningitis, leading to the disruption of intestinal barrier integrity in newborn pups and enhanced dissemination to the liver, spleen and brain. Consistent with these observations, disruption of cellulose production in ST95 augmented innate immune signalling and tissue neutrophil infiltration in a mouse model of urinary tract infection. Mutations that disrupt cellulose production were also identified in other virulent ExPEC STs, Shigella and Salmonella, suggesting a correlative association with many Enterobacteriaceae that cause severe human infection. Together, our findings provide an explanation for the emergence of hypervirulent Enterobacteriaceae clones.

Epidemiology and characterization of Providencia stuartii isolated from hospitalized patients in southern Brazil: a possible emerging pathogen

This study aimed to characterize the virulence factors and antimicrobial resistance of Providencia stuartii , an opportunistic pathogen that causes human infections. We examined 45 isolates of P. stuartii both genotypically and phenotypically by studying their adherence to HeLa cells, biofilm formation, cytotoxicity and antimicrobial resistance, and analysed their genomes for putative virulence and resistance genes. This study found that most isolates possessed multiple virulence genes, including fimA, mrkA, fptA, iutA, ireA and hlyA, and were cytotoxic to Vero cells. All the isolates were resistant to amoxicillin plus clavulanic acid, levofloxacin and sulfamethoxazole plus trimethoprim, and most were resistant to ceftriaxone and cefepime. All isolates harboured extended-spectrum beta-lactamase coding genes such as bla CTX-M-2 and 23/45(51.11 %) of them also harboured bla CTX-M-9. The gene KPC-2 (carbapenemase) was detected in 8/45(17.77 %) isolates. This study also found clonality among the isolates, indicating the possible spread of the pathogen among patients at the hospital. These results have significant clinical and epidemiological implications and emphasize the importance of a continued understanding of the virulence and antimicrobial resistance of this pathogen for the prevention and treatment of future infections.

Nordihydroguaiaretic Acid (NDGA) Inhibits CsgA Polymerization, Bacterial Amyloid Biogenesis, and Biofilm Formation

Escherichia coli and other Enterobacteriaceae thrive in robust biofilm communities through the coproduction of curli amyloid fibers and phosphoethanolamine cellulose. Curli promote adhesion to abiotic surfaces and plant and human host tissues and are associated with pathogenesis in urinary tract infection and food-borne illness. The production of curli in the host has also been implicated in the pathogenesis of neurodegenerative diseases. We report that the natural product nordihydroguaiaretic acid (NDGA) is effective as a curlicide in E. coli. NDGA prevents CsgA polymerization in vitro in a dose-dependent manner. NDGA selectively inhibits cell-associated curli assembly and inhibits uropathogenic E. coli biofilm formation. More broadly, this work emphasizes the ability to evaluate and identify bioactive amyloid assembly inhibitors by using the powerful gene-directed amyloid biogenesis machinery in E. coli.

Designed α-sheet peptides disrupt uropathogenic E. coli biofilms rendering bacteria susceptible to antibiotics and immune cells

Uropathogenic Escherichia coli account for the largest proportion of nosocomial infections in the United States. Nosocomial infections are a major source of increased costs and treatment complications. Many infections are biofilm associated, rendering antibiotic treatments ineffective or cause additional complications (e.g., microbiome depletion). This work presents a potentially complementary non-antibiotic strategy to fight nosocomial infections by inhibiting the formation of amyloid fibrils, a proteinaceous structural reinforcement known as curli in E. coli biofilms. Despite extensive characterization of the fibrils themselves and their associated secretion system, mechanistic details of curli assembly in vivo remain unclear. We hypothesized that, like other amyloid fibrils, curli polymerization involves a unique secondary structure termed "α-sheet". Biophysical studies herein confirmed the presence of α-sheet structure in prefibrillar species of CsgA, the major component of curli, as it aggregated. Binding of synthetic α-sheet peptides to the soluble α-sheet prefibrillar species inhibited CsgA aggregation in vitro and suppressed amyloid fibril formation in biofilms. Application of synthetic α-sheet peptides also enhanced antibiotic susceptibility and dispersed biofilm-resident bacteria for improved uptake by phagocytic cells. The ability of synthetic α-sheet peptides to reduce biofilm formation, improve antibiotic susceptibility, and enhance clearance by macrophages has broad implications for combating biofilm-associated infections.

A high-throughput sequencing approach identifies immunotherapeutic targets for bacterial meningitis in neonates

BACKGROUND

Worldwide, Escherichia coli is the leading cause of neonatal Gram-negative bacterial meningitis, but full understanding of the pathogenesis of this disease is not yet achieved. Moreover, to date, no vaccine is available against bacterial neonatal meningitis.

METHODS

Here, we used Transposon Sequencing of saturated banks of mutants (TnSeq) to evaluate E. coli K1 genetic fitness in murine neonatal meningitis. We identified E. coli K1 genes encoding for factors important for systemic dissemination and brain infection, and focused on products with a likely outer-membrane or extra-cellular localization, as these are potential vaccine candidates. We used in vitro and in vivo models to study the efficacy of active and passive immunization.

RESULTS

We selected for further study the conserved surface polysaccharide Poly-β-(1-6)-N-Acetyl Glucosamine (PNAG), as a strong candidate for vaccine development. We found that PNAG was a virulence factor in our animal model. We showed that both passive and active immunization successfully prevented and/or treated meningitis caused by E. coli K1 in neonatal mice. We found an excellent opsonophagocytic killing activity of the antibodies to PNAG and in vitro these antibodies were also able to decrease binding, invasion and crossing of E. coli K1 through two blood brain barrier cell lines. Finally, to reinforce the potential of PNAG as a vaccine candidate in bacterial neonatal meningitis, we demonstrated that Group B Streptococcus, the main cause of neonatal meningitis in developed countries, also produced PNAG and that antibodies to PNAG could protect in vitro and in vivo against this major neonatal pathogen.

INTERPRETATION

Altogether, these results indicate the utility of a high-throughput DNA sequencing method to identify potential immunotherapy targets for a pathogen, including in this study a potential broad-spectrum target for prevention of neonatal bacterial infections.

FUNDINGS

ANR Seq-N-Vaq, Charles Hood Foundation, Hearst Foundation, and Groupe Pasteur Mutualité.

Polysaccharides from Vaccaria segetalis seeds reduce urinary tract infections by inhibiting the adhesion and invasion abilities of uropathogenic Escherichia coli

The seeds of Vaccaria segetalis (Neck.) are from a traditional medicinal plant Garcke, also called Wang-Bu-Liu-Xing in China. According to the Chinese Pharmacopoeia, the seeds of V. segetalis can be used for treating urinary system diseases. This study was designed to investigate the underlying mechanism of VSP (polysaccharides from Vaccaria segetalis) against urinary tract infections caused by uropathogenic Escherichia coli (UPEC). Here, both in vitro and in vivo infection models were established with the UPEC strain CFT073. Bacterial adhesion and invasion into bladder epithelial cells were analyzed. We found that VSP reduced the adhesion of UPEC to the host by inhibiting the expression of bacterial hair follicle adhesion genes. VSP also reduced the invasion of UPEC by regulating the uroplakins and Toll-like receptors of host epithelial cells. In addition, the swarming motility and flagella-mediated motility genes flhC, flhD and Flic of UPEC were diminished after VSP intervention. Taken together, our findings reveal a possible mechanism by which VSP interferes with the adhesion and invasion of UPEC.

Assessment of Bacterial Isolates from the Urine Specimens of Urinary Tract Infected Patient

Urinary tract infections (UTIs) maintained a serious public health concern, as did the growth in antibiotic resistance both between uropathogenic microorganisms. A regular assessment of the microbiological agents that cause UTIs, as well as their antimicrobial resistance, is essential for a tailored empirical antibiotic response. Knowing the variables that cause UTIs can help you intervene quickly and simply to get the condition under control. The most common infecting species in acute infection is Escherichia coli (E. coli). To strengthen infection control strategies, it is necessary to know the prevalence and location of UTI. The goal of this research is to measure the frequency of microorganisms isolated from patients with UTIs as well as the antimicrobial sensitivity characteristics of Gram-negative bacteria. The purpose of this research has been to evaluate the frequency of UTIs by extracting and characterizing the various bacterial etiological organisms, as well as to assess the factors linked to UTIs. The goal of this research is to identify, characterize, and establish the antibiotic susceptibility patterns of bacteria linked to urinary tract infections. Fresh collected urine specimen was taken from inpatients or outpatients in UTI cases and bacteriologically tested using conventional microbiological methods. The Kirby-Bauer disc diffusion method was used to create the antibiogram. Staphylococcus saprophyticus, Staphylococcus aureus (28%), and Escherichia coli (24.6%) were the most common isolates (20%). The evaluated agents' antibacterial activity was all in the following order: cefixime, ciprofloxacin, augmentin, gentamicin, ceftazidime, nitrofurantoin, ofloxacin, and cefuroxime. It was discovered that each and every one of the microbes exhibited varied degrees of resistance to the antibiotics nitrofurantoin, ciprofloxacin, and ofloxacin. Every type of bacteria, with the exception of those belonging to the genus Streptococcus, has a Multiple Antibiotic Resistance Index (MARI) that is more than 0.2. The first-line therapies for urinary tract infections (UTIs) in the region would consist of ciprofloxacin, ofloxacin, and nitrofurantoin. Lower urinary tract infections almost never result in problems if they are diagnosed and treated as soon as possible and in the correct manner. However, if treatment is not sought, a urinary tract infection can lead to serious complications.

Virulence, resistance and clonality of Proteus mirabilis isolated from patients with community-acquired urinary tract infection (CA-UTI) in Brazil

Urinary tract infections (UTIs) are among the most common human infections, both in hospitals and in communities. Proteus mirabilis is known to cause community-acquired urinary tract infection (CA-UTI) and is an important causative agent of nosocomial UTIs. The pathogenesis of this species is related to its ability to manifest virulence factors, such as biofilms, adhesion molecules, urease, proteases, siderophores, and toxins. In this study, we investigated the virulence, sensitivity to antimicrobials, and clonal relationship of 183 strains isolated from the urine of CA-UTI patients in Londrina, Paraná State, Brazil. A total of 100% of the strains were positive for hpmA, ptA, zapA, mrpA, pmfA, ireA, and atfA virulence genes. The ucaA gene was positive in 81.4% of the cases. The strains showed high rates of sensitivity to the evaluated antimicrobials, and only one was ESBL-positive. All the tested bacteria showed the capacity to form biofilms: 73.2% had a very strong intensity, while 25.7% had a strong intensity, and 1.1% had a moderate intensity. Regarding clonality, 40 clonal clusters were found among the microorganisms tested. Our results showed that strains of P. mirabilis isolated from CA-UTI patients have several virulence factors. Although the urinary clinical isolates studied showed high sensitivity to antimicrobials, the strains showed a strong capacity to form biofilms, making antibiotic therapy difficult. In addition, it was observed that there were clones of P. mirabilis circulating in the city of Londrina.

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All strains presented a variety of virulence genes.

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It was observed that there were clones of P. mirabilis circulating.

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98.1% of strains produced strong or very strong biofilm.

Persistent Bacteriuria and Antibodies Recognizing Curli/eDNA Complexes From Escherichia coli Are Linked to Flares in Systemic Lupus Erythematosus

OBJECTIVE

Infections contribute to morbidity and mortality in systemic lupus erythematosus (SLE). Uropathogenic Escherichia coli (UPEC) are known to trigger urinary tract infections (UTIs) and form biofilms, which are multicellular communities of bacteria that are strengthened by amyloids such as curli. We previously reported that curli naturally form complexes with bacterial extracellular DNA (eDNA), and these curli/eDNA complexes induce hallmark features of lupus in mouse models. The present study was undertaken to investigate whether anti-curli/eDNA complex antibodies play a role in the pathogenesis of SLE or development of flares in SLE.

METHODS

In total, 96 SLE patients who met at least 4 Systemic Lupus International Collaborating Clinics disease criteria were investigated. Anti-curli/eDNA complex antibodies in the plasma were tested for both IgG and IgA subclasses. Results were compared to that in 54 age-, sex-, and race/ethnicity-matched healthy controls. Correlations of the levels of anti-curli/eDNA antibodies with clinical parameters, lupus disease status, and frequency of bacteriuria were assessed.

RESULTS

Anti-curli/eDNA antibodies were detected in the plasma of SLE patients and healthy controls, and their levels correlated with the presence of asymptomatic persistent bacteriuria and occurrence of disease flares in lupus patients. Persistent bacteriuria contained curli-producing UPEC, and this was associated with an inflammatory phenotype. Finally, curli/eDNA complexes cross-reacted with lupus autoantigens, such as double-stranded DNA, in binding autoantibodies.

CONCLUSION

These results suggest that UTIs and persistent bacteriuria are environmental triggers of lupus and its flares. Antibodies against curli/eDNA could serve as a sign of systemic exposure to bacterial products in SLE.

NMR insights into the pre-amyloid ensemble and secretion targeting of the curli subunit CsgA

The biofilms of Enterobacteriaceae are fortified by assembly of curli amyloid fibres on the cell surface. Curli not only provides structural reinforcement, but also facilitates surface adhesion. To prevent toxic intracellular accumulation of amyloid precipitate, secretion of the major curli subunit, CsgA, is tightly regulated. In this work, we have employed solution state NMR spectroscopy to characterise the structural ensemble of the pre-fibrillar state of CsgA within the bacterial periplasm, and upon recruitment to the curli pore, CsgG, and the secretion chaperone, CsgE. We show that the N-terminal targeting sequence (N) of CsgA binds specifically to CsgG and that its subsequent sequestration induces a marked transition in the conformational ensemble, which is coupled to a preference for CsgE binding. These observations lead us to suggest a sequential model for binding and structural rearrangement of CsgA at the periplasmic face of the secretion machinery.

Curli of Uropathogenic Escherichia coli Enhance Urinary Tract Colonization as a Fitness Factor

Curli, a type of fimbriae widely distributed in uropathogenic Escherichia coli (UPEC), are involved in adhesion to human bladder cell surfaces and biofilm development. The role of UPEC curli was evaluated in a murine model of urinary tract infection. The aim of this study was to establish the role of curli in C57BL/6 mice transurethrally infected with curli-producing and non-curli-producing UPEC strains. We confirmed that curli enhanced UPEC colonization in the urinary tract, resulting in damage to both the bladder and kidney. Intranasal immunization with recombinant CsgA protein protected against colonization by curli-producing UPEC in the urinary tract. Quantification of cytokines from urinary tract organs showed increases in interleukin-6 and tumor necrosis factor (TNF) release in the kidneys 48 h postinfection with curli-producing UPEC. By contrast, mice infected with non-curli-producing UPEC showed the highest release of interleukin-6, -10, and -17A and TNF. Curli may obscure other fimbriae and LPS, preventing interactions with Toll-like receptors. When intranasal immunization with recombinant FimH and PapG proteins and subsequent infection with this strain were performed, cytokine quantification showed a decrease in the stimulation and release by the uroepithelium. Thus, curli are amyloid-like fimbriae that enhances colonization in the urinary tract and a possible fitness factor.

Phosphoethanolamine cellulose enhances curli-mediated adhesion of uropathogenic Escherichia coli to bladder epithelial cells

Uropathogenic Escherichia coli (UPEC) are the major causative agents of urinary tract infections, employing numerous molecular strategies to contribute to adhesion, colonization, and persistence in the bladder niche. Identifying strategies to prevent adhesion and colonization is a promising approach to inhibit bacterial pathogenesis and to help preserve the efficacy of available antibiotics. This approach requires an improved understanding of the molecular determinants of adhesion to the bladder urothelium. We designed experiments using a custom-built live cell monolayer rheometer (LCMR) to quantitatively measure individual and combined contributions of bacterial cell surface structures [type 1 pili, curli, and phosphoethanolamine (pEtN) cellulose] to bladder cell adhesion. Using the UPEC strain UTI89, isogenic mutants, and controlled conditions for the differential production of cell surface structures, we discovered that curli can promote stronger adhesive interactions with bladder cells than type 1 pili. Moreover, the coproduction of curli and pEtN cellulose enhanced adhesion. The LCMR enables the evaluation of adhesion under high-shear conditions to reveal this role for pEtN cellulose which escaped detection using conventional tissue culture adhesion assays. Together with complementary biochemical experiments, the results support a model wherein cellulose serves a mortar-like function to promote curli association with and around the bacterial cell surface, resulting in increased bacterial adhesion strength at the bladder cell surface.

Discovery of New Genes Involved in Curli Production by a Uropathogenic Escherichia coli Strain from the Highly Virulent O45:K1:H7 Lineage

Curli are bacterial surface-associated amyloid fibers that bind to the dye Congo red (CR) and facilitate uropathogenic Escherichia coli (UPEC) biofilm formation and protection against host innate defenses. Here we sequenced the genome of the curli-producing UPEC pyelonephritis strain MS7163 and showed it belongs to the highly virulent O45:K1:H7 neonatal meningitis-associated clone. MS7163 produced curli at human physiological temperature, and this correlated with biofilm growth, resistance of sessile cells to the human cationic peptide cathelicidin, and enhanced colonization of the mouse bladder. We devised a forward genetic screen using CR staining as a proxy for curli production and identified 41 genes that were required for optimal CR binding, of which 19 genes were essential for curli synthesis. Ten of these genes were novel or poorly characterized with respect to curli synthesis and included genes involved in purine de novo biosynthesis, a regulator that controls the Rcs phosphorelay system, and a novel repressor of curli production (referred to as rcpA). The involvement of these genes in curli production was confirmed by the construction of defined mutants and their complementation. The mutants did not express the curli major subunit CsgA and failed to produce curli based on CR binding. Mutation of purF (the first gene in the purine biosynthesis pathway) and rcpA also led to attenuated colonization of the mouse bladder. Overall, this work has provided new insight into the regulation of curli and the role of these amyloid fibers in UPEC biofilm formation and pathogenesis.

Uropathogenic Escherichia coli (UPEC) strains are the most common cause of urinary tract infection, a disease increasingly associated with escalating antibiotic resistance. UPEC strains possess multiple surface-associated factors that enable their colonization of the urinary tract, including fimbriae, curli, and autotransporters. Curli are extracellular amyloid fibers that enhance UPEC virulence and promote biofilm formation. Here we examined the function and regulation of curli in a UPEC pyelonephritis strain belonging to the highly virulent O45:K1:H7 neonatal meningitis-associated clone. Curli expression at human physiological temperature led to increased biofilm formation, resistance of sessile cells to the human cationic peptide LL-37, and enhanced bladder colonization. Using a comprehensive genetic screen, we identified multiple genes involved in curli production, including several that were novel or poorly characterized with respect to curli synthesis. In total, this study demonstrates an important role for curli as a UPEC virulence factor that promotes biofilm formation, resistance, and pathogenesis.

Exploring Proteins Containing Amyloidogenic Regions in the Proteomes of Bacteria of the Order Rhizobiales

Amyloids are protein fibrils with a highly ordered spatial structure called cross-β. To date, amyloids were shown to be implicated in a wide range of biological processes, both pathogenic and functional. In bacteria, functional amyloids are involved in forming biofilms, storing toxins, overcoming the surface tension, and other functions. Rhizobiales represent an economically important group of Alphaproteobacteria, various species of which are not only capable of fixing nitrogen in the symbiosis with leguminous plants but also act as the causative agents of infectious diseases in animals and plants. Here, we implemented bioinformatic screening for potentially amyloidogenic proteins in the proteomes of more than 80 species belonging to the order Rhizobiales. Using SARP (Sequence Analysis based on the Ranking of Probabilities) and Waltz bioinformatic algorithms, we identified the biological processes, where potentially amyloidogenic proteins are overrepresented. We detected protein domains and regions associated with amyloidogenic sequences in the proteomes of various Rhizobiales species. We demonstrated that amyloidogenic regions tend to occur in the membrane or extracellular proteins, many of which are involved in pathogenesis-related processes, including adhesion, assembly of flagellum, and transport of siderophores and lipopolysaccharides, and contain domains typical of the virulence factors (hemolysin, RTX, YadA, LptD); some of them (rhizobiocins, LptD) are also related to symbiosis.

M60-like metalloprotease domain of the Escherichia coli YghJ protein forms amyloid fibrils

Amyloids are protein fibrils with a characteristic spatial structure. Amyloids were long perceived as the pathogens involved in a set of lethal diseases in humans and animals. In recent decades, it has become clear that amyloids represent a quaternary protein structure that is not only pathological but also functionally important and is widely used by different organisms, ranging from archaea to animals, to implement diverse biological functions. The greatest biological variety of amyloids is found in prokaryotes, where they control the formation of biofilms and cell wall sheaths, facilitate the overcoming of surface tension, and regulate the metabolism of toxins. Several amyloid proteins were identified in the important model, biotechnological and pathogenic bacterium Escherichia coli. In previous studies, using a method for the proteomic screening and identification of amyloids, we identified 61 potentially amyloidogenic proteins in the proteome of E. coli. Among these proteins, YghJ was the most enriched with bioinformatically predicted amyloidogenic regions. YghJ is a lipoprotein with a zinc metalloprotease M60-like domain that is involved in mucin degradation in the intestine as well as in proinflammatory responses. In this study, we analyzed the amyloid properties of the YghJ M60-like domain and demonstrated that it forms amyloid-like fibrils in vitro and in vivo.

Thiol Starvation Induces Redox-Mediated Dysregulation of Escherichia coli Biofilm Components

A hallmark of bacterial biofilms is the production of an extracellular matrix (ECM) that encases and protects the community from environmental stressors. Biofilm formation is an integral portion of the uropathogenic Escherichia coli (UPEC) life cycle. Approximately 2% of UPEC isolates are cysteine auxotrophs. Here, we investigated how cysteine homeostasis impacted UPEC UTI89 strain biofilm formation and, specifically, the production of the ECM components curli and cellulose. Cysteine auxotrophs produced less cellulose and slightly more curli compared to wild-type (WT) strains, and cysteine auxotrophs formed smooth, nonrugose colonies. Cellulose production was restored in cysteine auxotrophs when YfiR was inactivated. YfiR is a redox-sensitive regulator of the diguanylate cyclase, YfiN. The production of curli, a temperature-regulated appendage, was independent of temperature in UTI89 cysteine auxotrophs. In a screen of UPEC isolates, we found that ∼60% of UPEC cysteine auxotrophs produced curli at 37°C, but only ∼2% of cysteine prototrophic UPEC isolates produced curli at 37°C. Interestingly, sublethal concentrations of amdinocillin and trimethoprim-sulfamethoxazole inhibited curli production, whereas strains auxotrophic for cysteine continued to produce curli even in the presence of amdinocillin and trimethoprim-sulfamethoxazole. The dysregulation of ECM components and resistance to amdinocillin in cysteine auxotrophs may be linked to hyperoxidation, since the addition of exogenous cysteine or glutathione restored WT biofilm phenotypes to mutants unable to produce cysteine and glutathione.IMPORTANCE Uropathogenic Escherichia coli (UPEC) bacteria are the predominant causative agent of urinary tract infections (UTIs). UTIs account for billions of dollars of financial burden annually to the health care industry in the United States. Biofilms are an important aspect of the UPEC pathogenesis cascade and for the establishment of chronic infections. Approximately 2% of UPEC isolates from UTIs are cysteine auxotrophs, yet there is relatively little known about the biofilm formation of UPEC cysteine auxotrophs. Here we show that cysteine auxotrophs have dysregulated biofilm components due to a change in the redox state of the periplasm. Additionally, we show the relationship between cysteine auxotrophs, biofilms, and antibiotics frequently used to treat UTIs.

Ciprofloxacin resistance in uropathogenic Escherichia coli isolates causing community-acquired urinary infections in Brasília, Brazil

OBJECTIVES

Considering the global concern of ciprofloxacin resistance, the aim of this study was to evaluate the characteristics of ciprofloxacin-resistant (CIP-R) Escherichia coli isolated from patients with community-acquired urinary tract infections (UTIs) in Brasília, Brazil.

METHODS

CIP-R E. coli isolated from different outpatients between July 2013 and April 2014 in a tertiary hospital were analysed for antibiotic resistance profile, phylotype, uropathogenic E. coli (UPEC) virulence genes, clonal relationship by enterobacterial repetitive intergenic consensus PCR (ERIC-PCR), and multilocus sequence typing (MLST).

RESULTS

Among the 324 UPEC analysed, 263 (81.2%) were ciprofloxacin-sensitive and 61 (18.8%) were CIP-R. Antibiogram analysis of the 61 CIP-R strains showed that 45 (73.8%) were also multidrug-resistant. The most prevalent phylogroups were A and B2 (26/61 and 18/61, respectively). traT (53/61) and aer-traT (24/61) were the most common gene and genotype observed. Dendrogram analysis found that multidrug resistance and virulence genes were distributed among CIP-R strains independently of clonality and phylogroup. Six ERIC clusters (strains sharing ≥85% genetic similarity) were observed. MLST analysis of all strains of each cluster identified sequence types (STs) associated with worldwide antimicrobial resistance dissemination, including B2-ST131 and ST410, as well as STs not yet associated with antimicrobial resistance propagation, such as ST1725 and ST179.

CONCLUSIONS

These results demonstrate that ciprofloxacin resistance dissemination by UPEC causing community-acquired UTIs was associated with multidrug resistance and was promoted by pandemic and non-pandemic STs, a concerning scenario for the local population.

Expression of Curli by Escherichia coli O157:H7 Strains Isolated from Patients during Outbreaks Is Different from Similar Strains Isolated from Leafy Green Production Environments

We previously reported that the strains of Escherichia coli O157:H7 (EcO157) that survived longer in austere soil environment lacked expression of curli, a fitness trait linked with intestinal colonization. In addition, the proportion of curli-positive variants of EcO157 decreased with repeated soil exposure. Here we evaluated 84 and 176 clinical strains from outbreaks and sporadic infections in the US, plus 211 animal fecal and environmental strains for curli expression. These shiga-toxigenic strains were from 328 different genotypes, as characterized by multi-locus variable-number tandem-repeat analysis (MLVA). More than half of the fecal strains (human and animal) and a significant proportion of environmental isolates (82%) were found to lack curli expression. EcO157 strains from several outbreaks linked with the consumption of contaminated apple juice, produce, hamburgers, steak, and beef were also found to lack curli expression. Phylogenetic analysis of fecal strains indicates curli expression is distributed throughout the population. However, a significant proportion of animal fecal isolates (84%) gave no curli expression compared to human fecal isolates (58%). In addition, analysis of environmental isolates indicated nearly exclusive clustering of curli expression to a single branch of the minimal spanning tree. This indicates that curli expression depends primarily upon the type of environmental exposure and the isolation source, although genotypic differences also contribute to clonal variation in curli. Furthermore, curli-deficient phenotype appears to be a selective trait for survival of EcO157 in agricultural environments.

Dimeric and Trimeric Fusion Proteins Generated with Fimbrial Adhesins of Uropathogenic Escherichia coli

Urinary tract infections (UTIs) are associated with high rates of morbidity and mortality worldwide, and uropathogenic Escherichia coli (UPEC) is the main etiologic agent. Fimbriae assembled on the bacterial surface are essential for adhesion to the urinary tract epithelium. In this study, the FimH, CsgA, and PapG adhesins were fused to generate biomolecules for use as potential target vaccines against UTIs. The fusion protein design was generated using bioinformatics tools, and template fusion gene sequences were synthesized by GenScript in the following order fimH-csgA-papG-fimH-csgA (fcpfc) linked to the nucleotide sequence encoding the [EAAAK]₅ peptide. Monomeric (fimH, csgA, and papG), dimeric (fimH-csgA), and trimeric (fimH-csgA-papG) genes were cloned into the pLATE31 expression vector and generated products of 1040, 539, 1139, 1442, and 2444 bp, respectively. Fusion protein expression in BL21 E. coli was induced with 1 mM IPTG, and His-tagged proteins were purified under denaturing conditions and refolded by dialysis using C-buffer. Coomassie blue-stained SDS-PAGE gels and Western blot analysis revealed bands of 29.5, 11.9, 33.9, 44.9, and 82.1 kDa, corresponding to FimH, CsgA, PapG, FC, and FCP proteins, respectively. Mass spectrometry analysis by MALDI-TOF/TOF revealed specific peptides that confirmed the fusion protein structures. Dynamic light scattering analysis revealed the polydispersed state of the fusion proteins. FimH, CsgA, and PapG stimulated the release of 372–398 pg/mL IL-6; interestingly, FC and FCP stimulated the release of 464.79 pg/mL (p ≤ 0.018) and 521.24 pg/mL (p ≤ 0.002) IL-6, respectively. In addition, FC and FCP stimulated the release of 398.52 pg/mL (p ≤ 0.001) and 450.40 pg/mL (p ≤ 0.002) IL-8, respectively. High levels of IgA and IgG antibodies in human sera reacted against the fusion proteins, and under identical conditions, low levels of IgA and IgG antibodies were detected in human urine. Rabbit polyclonal antibodies generated against FimH, CsgA, PapG, FC, and FCP blocked the adhesion of E. coli strain CFT073 to HTB5 bladder cells. In conclusion, the FC and FCP proteins were highly stable, demonstrated antigenic properties, and induced cytokine release (IL-6 and IL-8); furthermore, antibodies generated against these proteins showed protection against bacterial adhesion.

The Biology of the Escherichia coli Extracellular Matrix

Escherichia coli is one of the world's best-characterized organisms, because it has been extensively studied for over a century. However, most of this work has focused on E. coli grown under laboratory conditions that do not faithfully simulate its natural environments. Therefore, the historical perspectives on E. coli physiology and life cycle are somewhat skewed toward experimental systems that feature E. coli growing logarithmically in a test tube. Typically a commensal bacterium, E. coli resides in the lower intestines of a slew of animals. Outside of the lower intestine, E. coli can adapt and survive in a very different set of environmental conditions. Biofilm formation allows E. coli to survive, and even thrive, in environments that do not support the growth of planktonic populations. E. coli can form biofilms virtually everywhere: in the bladder during a urinary tract infection, on in-dwelling medical devices, and outside of the host on plants and in the soil. The E. coli extracellular matrix (ECM), primarily composed of the protein polymer named curli and the polysaccharide cellulose, promotes adherence to organic and inorganic surfaces and resistance to desiccation, the host immune system, and other antimicrobials. The pathways that govern E. coli biofilm formation, cellulose production, and curli biogenesis will be discussed in this article, which concludes with insights into the future of E. coli biofilm research and potential therapies.

Structure, Function, and Assembly of Adhesive Organelles by Uropathogenic Bacteria

Bacteria assemble a wide range of adhesive proteins, termed adhesins, to mediate binding to receptors and colonization of surfaces. For pathogenic bacteria, adhesins are critical for early stages of infection, allowing the bacteria to initiate contact with host cells, colonize different tissues, and establish a foothold within the host. The adhesins expressed by a pathogen are also critical for bacterial-bacterial interactions and the formation of bacterial communities, including biofilms. The ability to adhere to host tissues is particularly important for bacteria that colonize sites such as the urinary tract, where the flow of urine functions to maintain sterility by washing away non-adherent pathogens. Adhesins vary from monomeric proteins that are directly anchored to the bacterial surface to polymeric, hair-like fibers that extend out from the cell surface. These latter fibers are termed pili or fimbriae, and were among the first identified virulence factors of uropathogenic Escherichia coli. Studies since then have identified a range of both pilus and non-pilus adhesins that contribute to bacterial colonization of the urinary tract, and have revealed molecular details of the structures, assembly pathways, and functions of these adhesive organelles. In this review, we describe the different types of adhesins expressed by both Gram-negative and Gram-positive uropathogens, what is known about their structures, how they are assembled on the bacterial surface, and the functions of specific adhesins in the pathogenesis of urinary tract infections.

The lysis cassette of DLP12 defective prophage is regulated by RpoE

Expression of the lysis cassette (essD, ybcT, rzpD/rzoD) from the defective lambdoid prophage at the 12th minute of Escherichia coli's genome (DLP12) is required in some strains for proper curli expression and biofilm formation. Regulating production of the lytic enzymes encoded by these genes is critical for maintaining cell wall integrity. In lambdoid phages, late-gene regulation is mediated by the vegetative sigma factor RpoD and the lambda antiterminator Qλ. We previously demonstrated that DLP12 contains a Q-like protein (QDLP12) that positively regulates transcription of the lysis cassette, but the sigma factor responsible for this transcription initiation remained to be elucidated. In silico analysis of essDp revealed the presence of a putative - 35 and - 10 sigma site recognized by the extracytoplasmic stress response sigma factor, RpoE. In this work, we report that RpoE overexpression promoted transcription from essDp in vivo, and in vitro using purified RNAP. We demonstrate that the - 35 region is important for RpoE binding in vitro and that this region is also important for QDLP12-mediated transcription of essDp in vivo. A bacterial two-hybrid assay indicated that QDLP12 and RpoE physically interact in vivo, consistent with what is seen for Qλ and RpoD. We propose that RpoE regulates transcription of the DLP12 lysis genes through interaction with QDLP12 and that proper expression is dependent on an intact - 35 sigma region in essDp. This work provides evidence that the unique Q-dependent regulatory mechanism of lambdoid phages has been co-opted by E. coli harbouring defective DLP12 and has been integrated into the tightly controlled RpoE regulon.

Human Urinary Composition Controls Antibacterial Activity of Siderocalin

During Escherichia coli urinary tract infections, cells in the human urinary tract release the antimicrobial protein siderocalin (SCN; also known as lipocalin 2, neutrophil gelatinase-associated lipocalin/NGAL, or 24p3). SCN can interfere with E. coli iron acquisition by sequestering ferric iron complexes with enterobactin, the conserved E. coli siderophore. Here, we find that human urinary constituents can reverse this relationship, instead making enterobactin critical for overcoming SCN-mediated growth restriction. Urinary control of SCN activity exhibits wide ranging individual differences. We used these differences to identify elevated urinary pH and aryl metabolites as key biochemical host factors controlling urinary SCN activity. These aryl metabolites are well known products of intestinal microbial metabolism. Together, these results identify an innate antibacterial immune interaction that is critically dependent upon individualistic chemical features of human urine.

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.