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

Progress toward a vaccine for extraintestinal pathogenic E. coli (ExPEC) II: efficacy of a toxin-autotransporter dual antigen approach

Extraintestinal pathogenic Escherichia coli (ExPEC) is a leading cause of worldwide morbidity and mortality, the top cause of antimicrobial-resistant (AMR) infections, and the most frequent cause of life-threatening sepsis and urinary tract infections (UTI) in adults. The development of an effective and universal vaccine is complicated by this pathogen's pan-genome, its ability to mix and match virulence factors and AMR genes via horizontal gene transfer, an inability to decipher commensal from pathogens, and its intimate association and co-evolution with mammals. Using a pan virulome analysis of >20,000 sequenced E. coli strains, we identified the secreted cytolysin α-hemolysin (HlyA) as a high priority target for vaccine exploration studies. We demonstrate that a catalytically inactive pure form of HlyA, expressed in an autologous host using its own secretion system, is highly immunogenic in a murine host, protects against several forms of ExPEC infection (including lethal bacteremia), and significantly lowers bacterial burdens in multiple organ systems. Interestingly, the combination of a previously reported autotransporter (SinH) with HlyA was notably effective, inducing near complete protection against lethal challenge, including commonly used infection strains ST73 (CFT073) and ST95 (UTI89), as well as a mixture of 10 of the most highly virulent sequence types and strains from our clinical collection. Both HlyA and HlyA-SinH combinations also afforded some protection against UTI89 colonization in a murine UTI model. These findings suggest recombinant, inactive hemolysin and/or its combination with SinH warrant investigation in the development of an E. coli vaccine against invasive disease.

The presence of virulence factor genes downregulates uterine AQP3 and alters glutathione peroxidase activity and uterine histopathology in canine pyometra

Present study was designed to evaluate the role of virulence factor genes (papG, cnf1 and hylA) in the pathogenesis of canine pyometra. Antimicrobial susceptibility test and detection of virulence genes were performed Escherichia coli (E. coli) detected in uterine swab samples. Animals were divided into two groups based on the presence (VF+, n:14) or absence (VF-, n:7) of the virulence factor genes papG, cnf1 and hylA. Blood and tissue glutathione peroxidase activity, uterine histopathologic analysis and AQP3, ESR1, PGR, OXTR gene expressions were determined in both groups. Statistical analyses were performed using Stata version 15.1. All E. coli isolates were susceptible to amikacin, whereas resistant to ampicillin, amoxicillin/clavulanic acid and lincomycin. None of the isolates were susceptible to cefotaxime. E. coli isolates had at least one virulence gene. The most prevalent gene was fimH (100%), followed by fyuA (95.8%), usp (83.3%), sfa (75%), cnf1 and hlyA (70.8%) genes. Blood GPx activity was greater in VF+ animals. On the other hand, uterine tissue GPx activity was lower in VF+ group compared to the control group. Expression levels of AQP3 were upregulated more than fivefold in VF-dogs compared to the control group. In addition, AQP3 expression levels were found approximately threefold higher in VF (-) than VF (+) group (p < .05). Varying degree of inflammation noted for all animals with pyometra, but the presence of bacteria noted only in VF+ animals. In conclusion, the presence of virulence factor genes does not play a role in the histopathological degree of inflammation, the presence of bacteria was found to vary. Serum GPx activity increased in VF+ animals. While the hormone receptor expressions were similar, AQP expression was upregulated in the absence of virulence factor genes.

TusDCB, a sulfur transferase complex involved in tRNA modification, contributes to UPEC pathogenicity

tRNA modifications play a crucial role in ensuring accurate codon recognition and optimizing translation levels. While the significance of these modifications in eukaryotic cells for maintaining cellular homeostasis and physiological functions is well-established, their physiological roles in bacterial cells, particularly in pathogenesis, remain relatively unexplored. The TusDCB protein complex, conserved in γ-proteobacteria like Escherichia coli, is involved in sulfur modification of specific tRNAs. This study focused on the role of TusDCB in the virulence of uropathogenic E. coli (UPEC), a bacterium causing urinary tract infections. The findings indicate that TusDCB is essential for optimal production of UPEC's virulence factors, including type 1 fimbriae and flagellum, impacting the bacterium's ability to aggregate in bladder epithelial cells. Deletion of tusDCB resulted in decreased virulence against urinary tract infection mice. Moreover, mutant TusDCB lacking sulfur transfer activity and tusE- and mnmA mutants revealed the indispensability of TusDCB's sulfur transfer activity for UPEC pathogenicity. The study extends its relevance to highly pathogenic, multidrug-resistant strains, where tusDCB deletion reduced virulence-associated bacterial aggregation. These insights not only deepen our understanding of the interplay between tRNA sulfur modification and bacterial pathogenesis but also highlight TusDCB as a potential therapeutic target against UPEC strains resistant to conventional antimicrobial agents.

Characterization of a hemolytic and antibiotic-resistant Pseudomonas aeruginosa strain S3 pathogenic to fish isolated from Mahananda River in India

Virulent strain Pseudomonas aeruginosa isolated from Mahananda River exhibited the highest hemolytic activity and virulence factors and was pathogenic to fish as clinical signs of hemorrhagic spots, loss of scales, and fin erosions were found. S3 was cytotoxic to the human liver cell line (WRL-68) in the trypan blue dye exclusion assay. Genotype characterization using whole genome analysis showed that S3 was similar to P. aeruginosa PAO1. The draft genome sequence had an estimated length of 62,69,783 bp, a GC content of 66.3%, and contained 5916 coding sequences. Eight genes across the genome were predicted to be related to hemolysin action. Antibiotic resistance genes such as class C and class D beta-lactamases, fosA, APH, and catB were detected, along with the strong presence of multiple efflux system genes. This study shows that river water is contaminated by pathogenic P. aeruginosa harboring an array of virulence and antibiotic resistance genes which warrants periodic monitoring to prevent disease outbreaks.

Comparative genomic analysis of uropathogenic Escherichia coli strains from women with recurrent urinary tract infection

Introduction

Recurrent urinary tract infections (RUTIs) caused by uropathogenic Escherichia coli are costly public health problems impacting patients' quality of life.

Aim

In this work, a comparative genomics analysis of three clinical RUTI strains isolated from bladder biopsy specimens was performed.

Materials and methods

One hundred seventy-two whole genomes of urinary tract E. coli strains were selected from the NCBI database. The search for virulence factors, fitness genes, regions of interest, and genetic elements associated with resistance was manually carried out. The phenotypic characterization of antibiotic resistance, haemolysis, motility, and biofilm formation was performed. Moreover, adherence and invasion assays with human bladder HTB-5 cells, and transmission electron microscopy (TEM) were performed.

Results

The UTI-1_774U and UTI-3_455U/ST1193 strains were associated with the extraintestinal pathotypes, and the UTI-2_245U/ST295 strain was associated with the intestinal pathotype, according to a phylogenetic analysis of 172 E. coli urinary strains. The three RUTI strains were of clinical, epidemiological, and zoonotic relevance. Several resistance genes were found within the plasmids of these strains, and a multidrug resistance phenotype was revealed. Other virulence genes associated with CFT073 were not identified in the three RUTI strains (genes for type 1 and P fimbriae, haemolysin hlyA, and sat toxin). Quantitative adherence analysis showed that UTI-1_774U was significantly (p < 0.0001) more adherent to human bladder HTB-5 cells. Quantitative invasion analysis showed that UTI-2_245U was significantly more invasive than the control strains. No haemolysis or biofilm activity was detected in the three RUTI strains. The TEM micrographs showed the presence of short and thin fimbriae only in the UTI-2_245U strain.

Conclusion

The high variability and genetic diversity of the RUTI strains indicate that are a mosaic of virulence, resistance, and fitness genes that could promote recurrence in susceptible patients.

Native ApxIIA secreted by Actinobacillus pleuropneumoniae induces apoptosis in porcine alveolar macrophages dependent on concentration and acylation

Actinobacillus pleuropneumoniae is an important swine respiratory pathogen causing substantial economic losses to the global pig industry. The Apx toxins of A. pleuropneumoniae belong to the RTX toxin family and are major virulence factors. In addition to hemolysis and/or cytotoxicity via pore-forming activity, RTX toxins, such as ApxIA of A. pleuropneumoniae, have been reported to cause other effects on target cells, e.g., apoptosis. A. pleuropneumoniae ApxIIA is expressed by most serotypes and has moderate hemolytic and cytotoxic activities. In this study, porcine alveolar macrophages (3D4/21) were stimulated with different concentrations of purified native ApxIIA from the serotype 7 strain AP76 which only secretes ApxIIA. By observation of nuclear condensation via fluorescent staining and detection of apoptosis and necrosis by flow cytometry, it was found that high and low concentrations of native ApxIIA mainly caused necrosis or apoptosis of 3D4/21 cells, respectively. ApxIIA purified from an AP76 mutant with a deleted acetyltransferase gene (apxIIC) did not induce necrosis nor apoptosis. Western blot analysis using specific antibodies showed that a cleaved caspase 3 and activated capase 9 was detected after treatment of cells with a low concentration of native ApxIIA, while general or specific inhibitors of caspase 3, 8, 9 blocked these effects. ApxIIA-induced apoptosis of macrophages may be a mechanism of A. pleuropneumoniae to escape host immune clearance.

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.

Genomic epidemiology and antibiotic susceptibility profiling of uropathogenic Escherichia coli among children in the United States

Escherichia coli is the most common cause of urinary tract infections (UTIs) in children, and yet the underlying mechanisms of virulence and antibiotic resistance and the overall population structure of the species is poorly understood within this age group. To investigate whether uropathogenic E. coli (UPEC) from children who developed pyelonephritis carried specific genetic markers, we generated whole-genome sequence data for 96 isolates from children with UTIs. This included 57 isolates from children with either radiologically confirmed pyelonephritis or cystitis and 27 isolates belonging to the well-known multidrug-resistant sequence type ST131, selected to investigate their population structure and antibiotic resistance characteristics. We observed a UPEC population structure that is similar to those reported in adults. In comparison with prior investigations, we found that the full pap operon was more common among UPEC from pediatric cases of pyelonephritis. Further, in contrast with recent reports that the P-fimbriae adhesin-encoding papGII allele is substantially more prevalent in invasive UPEC from adults, we found papGII was common to both invasive and non-invasive UPEC from children. Among the set of ST131 isolates from children with UTIs, we found antibiotic resistance was correlated with known genetic markers of resistance, as in adults. Unexpectedly, we observed that fimH30, an allele of the fimbrial gene fimH often used as a proxy to type ST131 isolates into the most drug-resistant subclade C, was carried by some of the subclade A and subclade B isolates, suggesting that the fimH30 allele could confer a selective advantage for UPEC. IMPORTANCE Urinary tract infections (UTIs), which are most often caused by Escherichia coli, are not well studied in children. Here, we examine genetic characteristics that differentiate UTI-causing bacteria in children that either remain localized to the bladder or are involved in more serious kidney infections. We also examine patterns of antibiotic resistance among strains from children that are part of E. coli sequence type 131, a group of bacteria that commonly cause UTIs and are known to have high levels of drug resistance. This work provides new insight into the virulence and antibiotic resistance characteristics of the bacteria that cause UTIs in children.

Uropathogen and host responses in pyelonephritis

Urinary tract infections (UTIs) are among the most common bacterial infections seen in clinical practice. The ascent of UTI-causing pathogens to the kidneys results in pyelonephritis, which can trigger kidney injury, scarring and ultimately impair kidney function. Despite sizable efforts to understand how infections develop or are cleared in the bladder, our appreciation of the mechanisms by which infections develop, progress or are eradicated in the kidney is limited. The identification of virulence factors that are produced by uropathogenic Escherichia coli to promote pyelonephritis have begun to fill this knowledge gap, as have insights into the mechanisms by which kidney tubular epithelial cells oppose uropathogenic E. coli infection to prevent or eradicate UTIs. Emerging data also illustrate how specific cellular immune responses eradicate infection whereas other immune cell populations promote kidney injury. Insights into the mechanisms by which uropathogenic E. coli circumvent host immune defences or antibiotic therapy to cause pyelonephritis is paramount to the development of new prevention and treatment strategies to mitigate pyelonephritis and its associated complications.

The PapB/FocB family protein TosR acts as a positive regulator of flagellar expression and is required for optimal virulence of uropathogenic Escherichia coli

Uropathogenic Escherichia coli (UPEC) is a major causative agent of urinary tract infections. The bacteria internalize into the uroepithelial cells, where aggregate and form microcolonies. UPEC fimbriae and flagella are important for the formation of microcolonies in uroepithelial cells. PapB/FocB family proteins are small DNA-binding transcriptional regulators consisting of approximately 100 amino acids that have been reported to regulate the expression of various fimbriae, including P, F1C, and type 1 fimbriae, and adhesins. In this study, we show that TosR, a member of the PapB/FocB family is the activator of flagellar expression. The tosR mutant had similar expression levels of type 1, P and F1C fimbriae as the parent strain, but flagellar production was markedly lower than in the parent strain. Flagellin is a major component of flagella. The gene encoding flagellin, fliC, is transcriptionally activated by the sigma factor FliA. The fliA expression is induced by the flagellar master regulator FlhDC. The flhD and flhC genes form an operon. The promoter activity of fliC, fliA and flhD in the tosR mutant was significantly lower than in the parent strain. The purified recombinant TosR does not bind to fliC and fliA but to the upstream region of the flhD gene. TosR is known to bind to an AT-rich DNA sequence consisting of 29 nucleotides. The characteristic AT-rich sequence exists 550-578 bases upstream of the flhD gene. The DNA fragment lacking this sequence did not bind TosR. Furthermore, loss of the tosR gene reduced motility and the aggregation ability of UPEC in urothelial cells. These results indicate that TosR is a transcriptional activator that increases expression of the flhDC operon genes, contributing to flagellar expression and optimal virulence.

Genotypic characteristics of Uropathogenic Escherichia coli isolated from complicated urinary tract infection (cUTI) and asymptomatic bacteriuria-a relational analysis

Background

Uropathogenic Escherichia coli (UPEC) is the predominant agent causing various categories of complicated urinary tract infections (cUTI). Although existing data reveals that UPEC harboured numerous virulence determinants to aid its survival in the urinary tract, the reason behind the occurrence of differences in the clinical severity of uninary tract infections (UTI) demonstrated by the UPEC infection is poorly understood. Therefore, the present study aims to determine the distribution of virulence determinants and antimicrobial resistance among different phylogroups of UPEC isolated from various clinical categories of cUTI and asymptomatic bacteriuria (ASB) E. coli isolates. The study will also attempt a relational analysis of the genotypic characteristics of cUTI UPEC and ASB E. coli isolates.

Methods

A total of 141 UPEC isolates from cUTI and 160 ASB E. coli isolates were obtained from Universiti Malaya Medical Centre (UMMC). Phylogrouping and the occurrence of virulence genes were investigated using polymerase chain reaction (PCR). Antimicrobial susceptibility of the isolates to different classes of antibiotics was determined using the Kirby Bauer Disc Diffusion method.

Results

The cUTI isolates were distributed differentially among both Extraintestinal Pathogenic E. coli (ExPEC) and non-ExPEC phylogroups. Phylogroup B2 isolates were observed to possess the highest average aggregative virulence score (7.17), a probable representation of the capability to cause severe disease. Approximately 50% of the cUTI isolates tested in this study were multidrug resistant against common antibiotics used to treat UTI. Analysis of the occurrence of virulence genes among different cUTI categories demonstrated that UPEC isolates of pyelonephritis and urosepsis were highly virulent and had the highest average aggregative virulence scores of 7.80 and 6.89 respectively, compared to other clinical categories. Relational analysis of the occurrence of phylogroups and virulence determinants of UPEC and ASB E. coli isolates showed that 46.1% of UPEC and 34.3% of ASB E. coli from both categories were distributed in phylogroup B2 and had the highest average aggregative virulence score of 7.17 and 5.37, respectively. The data suggest that UPEC isolates which carry virulence genes from all four virulence genes groups studied (adhesions, iron uptake systems, toxins and capsule synthesis) and isolates from phylogroup B2 specifically could predispose to severe UTI involving the upper urinary tract. Therefore, specific analysis of the genotypic characteristics of UPEC could be further explored by incorporating the combination of virulence genes as a prognostic marker for predicting disease severity, in an attempt to propose a more evidence driven treatment decision-making for all UTI patients. This will go a long way in enhancing favourable therapeutic outcomes and reducing the antimicrobial resistance burden among UTI patients.

α-Hemolysin promotes uropathogenic E. coli persistence in Bladder epithelial cells Via abrogating bacteria-harboring lysosome acidification

There is a growing consensus that a significant proportion of recurrent urinary tract infections are linked to the persistence of uropathogens within the urinary tract and their re-emergence upon the conclusion of antibiotic treatment. Studies in mice and human have revealed that uropathogenic Escherichia coli (UPEC) can persist in bladder epithelial cells (BECs) even after the apparent resolution of the infection. Here, we found that, following the entry of UPEC into RAB27b+ fusiform vesicles in BECs, some bacteria escaped into the cytoplasmic compartment via a mechanism involving hemolysin A (HlyA). However, these UPEC were immediately recaptured within LC3A/B+ autophagosomes that matured into LAMP1+ autolysosomes. Thereafter, HlyA+ UPEC-containing lysosomes failed to acidify, which is an essential step for bacterial elimination. This lack of acidification was related to the inability of bacteria-harboring compartments to recruit V-ATPase proton pumps, which was attributed to the defragmentation of cytosolic microtubules by HlyA. The persistence of UPEC within LAMP1+ compartments in BECs appears to be directly linked to HlyA. Thus, through intravesicular instillation of microtubule stabilizer, this host defense response can be co-opted to reduce intracellular bacterial burden following UTIs in the bladder potentially preventing recurrence.

Uropathogenic Escherichia coli endeavors: an insight into the characteristic features, resistance mechanism, and treatment choice

Uropathogenic Escherichia coli (UPEC) are the strains diverted from the intestinal status and account mainly for uropathogenicity. This pathotype has gained specifications in structure and virulence to turn into a competent uropathogenic organism. Biofilm formation and antibiotic resistance play an important role in the organism's persistence in the urinary tract. Increased consumption of carbapenem prescribed for multidrug-resistant (MDR) and Extended-spectrum-beta lactamase (ESBL)-producing UPECs, has added to the expansion of resistance. The World Health Organization (WHO) and Centre for Disease Control (CDC) placed the Carbapenem-resistant Enterobacteriaceae (CRE) on their treatment priority lists. Understanding both patterns of pathogenicity, and multiple drug resistance may provide guidance for the rational use of anti-bacterial agents in the clinic. Developing an effective vaccine, adherence-inhibiting compounds, cranberry juice, and probiotics are non-antibiotical approaches proposed for the treatment of drug-resistant UTIs. We aimed to review the distinguishing characteristics, current therapeutic options and promising non-antibiotical approaches against ESBL-producing and CRE UPECs.

Alpha-Hemolysin from Staphylococcus aureus Obstructs Yeast-Hyphae Switching and Diminishes Pathogenicity in Candida albicans

The use of antibiotics can disrupt the body's natural balance and increase the susteptibility of patients towards fungal infections. Candida albicans is a dimorphic opportunistic fungal pathogen with niches similar to those of bacteria. Our aim was to study the interaction between this pathogen and bacteria to facilitate the control of C. albicans infection. Alpha-hemolysin (Hla), a protein secreted from Staphylococcus aureus, causes cell wall damage and impedes the yeast-hyphae transition in C. albicans. Mechanistically, Hla stimulation triggered the formation of reactive oxygen species that damaged the cell wall and mitochondria of C. albicans. The cell cycle was arrested in the G0/G1 phase, CDC42 was downregulated, and Ywp1 was upregulated, disrupting yeast hyphae switching. Subsequently, hyphae development was inhibited. In mouse models, C. albicans pretreated with Hla reduced the C. albicans burden in skin and vaginal mucosal infections, suggesting that S. aureus Hla can inhibit hyphal development and reduce the pathogenicity of candidiasis in vivo.

The Diversity of Escherichia coli Pathotypes and Vaccination Strategies against This Versatile Bacterial Pathogen

Escherichia coli (E. coli) is a gram-negative bacillus and resident of the normal intestinal microbiota. However, some E. coli strains can cause diseases in humans, other mammals and birds ranging from intestinal infections, for example, diarrhea and dysentery, to extraintestinal infections, such as urinary tract infections, respiratory tract infections, meningitis, and sepsis. In terms of morbidity and mortality, pathogenic E. coli has a great impact on public health, with an economic cost of several billion dollars annually worldwide. Antibiotics are not usually used as first-line treatment for diarrheal illness caused by E. coli and in the case of bloody diarrhea, antibiotics are avoided due to the increased risk of hemolytic uremic syndrome. On the other hand, extraintestinal infections are treated with various antibiotics depending on the site of infection and susceptibility testing. Several alarming papers concerning the rising antibiotic resistance rates in E. coli strains have been published. The silent pandemic of multidrug-resistant bacteria including pathogenic E. coli that have become more difficult to treat favored prophylactic approaches such as E. coli vaccines. This review provides an overview of the pathogenesis of different pathotypes of E. coli, the virulence factors involved and updates on the major aspects of vaccine development against different E. coli pathotypes.

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

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

Phenotypic Assessment of Clinical Escherichia coli Isolates as an Indicator for Uropathogenic Potential

For women in the United States, urinary tract infections (UTIs) are the most frequent diagnosis in emergency departments, comprising 21.3% of total visits. Uropathogenic Escherichia coli (UPEC) causes ~80% of uncomplicated UTIs. To combat this public health issue, it is vital to characterize UPEC strains as well as to differentiate them from commensal strains to reduce the overuse of antibiotics. It has been challenging to determine a consistent genetic signature that clearly distinguishes UPEC from other E. coli strains. Therefore, we examined whether phenotypic data could be predictive of uropathogenic potential. We screened 13 clinical strains of UPEC, isolated from cases of uncomplicated UTI in young otherwise healthy women, in a series of microbiological phenotypic assays using UPEC prototype strain CFT073 and nonpathogenic E. coli strain MG1655 K-12 as controls. Phenotypes included adherence, iron acquisition, biofilm formation, human serum resistance, motility, and stress resistance. By use of a well-established experimental mouse model of UTI, these data were able to predict the severity of the bacterial burden in both the urine and bladders. Multiple linear regression using three different phenotypic assays, i.e., growth in minimal medium, siderophore production, and type 1 fimbrial expression, was predictive of bladder colonization (adjusted R² = 0.6411). Growth in ex vivo human urine, hemagglutination of red blood cells, and motility modeled urine colonization (adjusted R² = 0.4821). These results showcase the utility of phenotypic characterization to predict the severity of infection that these strains may cause. We predict that these methods will also be applicable to other complex, genetically redundant, pathogens. IMPORTANCE Urinary tract infections are the second leading infectious disease worldwide, occurring in over half of the female population during their lifetime. Most infections are caused by uropathogenic Escherichia coli (UPEC) strains. These strains can establish a reservoir in the gut, in which they do not cause disease but, upon introduction to the urinary tract, can infect the host and elicit pathogenesis. Clinically, it would be beneficial to screen patient E. coli strains to understand their pathogenic potential, which may lead to the administration of prophylactic antibiotic treatment for those with increased risk. Others have proposed the use of PCR-based genetic screening methods to detect UPEC strains and differentiate them from other E. coli pathotypes; however, this method has not yielded a consistent uropathogenic genetic signature. Here, we used phenotypic characteristics such as growth rate, siderophore production, and expression of fimbriae to better predict uropathogenic potential.

Genomic and pathogenic characterization of RTX toxin producing Rodentibacter sp. that is closely related to Rodentibacter haemolyticus

Rodentibacter spp. are opportunistic pathogens that are often isolated from the upper respiratory tracts of laboratory rodents. In particular, R. pneumotropicus and R. heylii require considerable caution in rodent colonies, as they cause lethal pneumonia in rodents. A new species, R. haemolyticus, has recently been classified in the genus, and a very closely related strain, Rodentibacter sp. strain JRC, has been isolated in Japan. This study focused on strain JRC by performing genomic and pathogenic analyses. Draft genome sequencing of strain JRC identified several genes coding for putative virulent proteins, including hemolysin and adhesin. Furthermore, we found a new RTX (repeats-in-structural toxin) toxin gene in the genome, which was predicted to produce a critical virulence factor (RTXIA) similar to Enterobacteriaceae. The concentrated culture supernatant containing RTX toxin (RTXIA) showed cytotoxicity toward RAW264.7 cells. Pre-incubation with anti-CD11a attenuated the cytolysis, suggesting that the concentrated culture supernatant containing RTXIA is cell surface LFA-1 mediated cytolysin. Experimental infection of strain JRC intranasally with 5 female BALB/c-Rag2^-/- mice showed 60% lethality and was not significantly different from those of R. pneumotropicus ATCC 35149^T using the log-rank test. Combined with our finding that RTXIA has an almost identical amino acid sequence (98% identity) to that of R. haemolyticus 1625/19^T, these results strongly suggest that RTXIA-producing strain JRC (and related R. haemolyticus) is pathogenic to immunodeficient rodents, and both agents should be excluded in laboratory rodent colonies.

A comparative study of the clonal diversity and virulence characteristics of uropathogenic Escherichia coli isolated from Australian and Turkish (Turkey) children and adults with urinary tract infections

Introduction

The virulence-associated gene (VAG) repertoire and clonal organization of uropathogenic Escherichia coli (UPEC) strains is influenced by host demographic, geographic locale, and the setting of urinary tract infection (UTI). Nevertheless, a direct comparison of these features among Australian and Turkish UPEC remains unexplored. Accordingly, this study investigated the clonal composition and virulence characteristics of a collection of UPEC isolated from Australian and Turkish UTI patients.

Methods

A total of 715 UPEC strains isolated from Australian (n=361) and Turkish (n=354) children and adults with hospital (HA)- and community-acquired (CA)-UTIs were included in this study. Typing of the strains using RAPD-PCR and PhPlate fingerprinting grouped all strains into 25 clonal groups (CGs). CG representatives were phylogrouped and screened for the presence of 18 VAGs associated with extraintestinal pathogenic E. coli.

Results

Turkish UPEC strains were characterized by high clonal diversity and predominance of the phylogroup D, while few distinct clonal groups with phylogenetic group B2 backgrounds dominated among the Australian strains. Twelve identical CGs were shared between ≥1 patient group from either country. Australian strains, particularly those isolated from children with HA-UTI, showed higher virulence potential than their Turkish counterparts, carrying significantly more genes associated with adhesion, iron acquisition and capsule biosynthesis.

Conclusions

This study identified identical CGs of UPEC causing HA- and CA-UTIs among Australian and Turkish UTI patients. These CGs frequently carried VAGs associated with adhesion, iron acquisition, immune evasion, and toxin production, which may contribute to their ability to disseminate internationally and to cause UTI.

Antibiotic-resistant pathogenic bacterial isolates from patients attending the outpatient department of university of Cape Coast hospital, Ghana: A retrospective study between 2013-2015

Uropathogenic Escherichia coli (E. coli) is an important urinary tract infection (UTI) that has been associated with both complicated and uncomplicated disease conditions. The global emergence of multiple drug-resistant (MDR) and extended-spectrum β-lactamase (ESBL) is of public health concern as the resistance limits the current treatment options. The objective of this study was to analyze the antibiotic-resistant patterns among the uropathogenic E. coli isolates at the University of Cape Coast (UCC) hospital between 2013 and 2015 as baseline data to understand the current antibiotic resistance situation within UCC and its environs. A retrospective cross-sectional study of bacteria isolates at UCC hospital from January 2013 to December 2015 were analyzed. A standard biochemical and antibiotic susceptibility tests were performed using Kirby-Bauer NCCLs modified disc diffusion technique. The network of interaction between pathogenic isolates and antibiotic resistance was performed using Cytoscape software. Statistical significance was tested using ANOVA and one-sample Wilcoxon test. The overall E. coli prevalence was 15.76% (32/203); females had the highest infection of 17.33% (26/150) compared to male subjects who had 11.32% (6/53) out of all the pathogenic infections. The E. coli prevalence among the age categories were 2/21 (9.52%), 27/154 (17.53%) and 4/21 (19.05%) among ≤20 years, 21-40 years and 41-60 years respectively. The isolated resistant pathogens exhibited different antibiotic resistance patterns. An interaction network of nodes connecting to other nodes indicating positive correlations between the pathogens and antibiotic resistance was established. Escherichia coli, Citrobacter spp, Klebsiella spp among other isolated pathogens formed higher centrality in the network of interaction with antibiotic resistance. The individual E. coli isolates showed a significant difference in the mean ± SD (95% CI) pattern of antibiotic resistance, 2.409±1.205 (1.828-2.990), χ2 = 36.68, p<0.0001. In conclusion, the study reports the interaction of E. coli isolates at UCC hospital and its antibiotic-resistant status between 2013 and 2015. This data forms the baseline information for assessing the current antibiotic status in UCC and its environs.

Genotypic assay to determine some virulence factors of Uropathogenic E. coli (UPEC) isolates

A total of 179 urine samples were collected from patients suffering from urinary tract infections were admitted and visit Al-Hilla General Teaching Hospital in Al-Hilla City, during a period from April 2021 to December 2021, from both sex (male and female). Out of 179,123 (68.7%) were positive culture, whereas 56 (31.3%) samples showed no bacterial growth, To confirm the identification of E. coli by use selective media (EMB agar medium, biochemical tests, automated Vitek 2 system and 16s RNA specific primer by the presence of (1492 bp) compared with allelic ladder, it was found that, E. coli were deliberated the main an etiological causes UTI to other types bacteria which constitute 56/123 (45.5%), [45/56 (80.4%) from female and 11/56 (19.6%) from male], while 67/123 (54.4%) were related to other types of bacteria. Molecular detection of some virulence factors genes were studied, out of 56 E. coli isolates, hlyA gene was detected in 21/56 (37.5%) isolates by the presence of (1177 bp) and sat gene was detected in 35/56 (62.5%) isolates by the presence of (410 bp) compared with allelic ladder.

Bacterial pore-forming toxins

Pore-forming toxins (PFTs) are widely distributed in both Gram-negative and Gram-positive bacteria. PFTs can act as virulence factors that bacteria utilise in dissemination and host colonisation or, alternatively, they can be employed to compete with rival microbes in polymicrobial niches. PFTs transition from a soluble form to become membrane-embedded by undergoing large conformational changes. Once inserted, they perforate the membrane, causing uncontrolled efflux of ions and/or nutrients and dissipating the protonmotive force (PMF). In some instances, target cells intoxicated by PFTs display additional effects as part of the cellular response to pore formation. Significant progress has been made in the mechanistic description of pore formation for the different PFTs families, but in several cases a complete understanding of pore structure remains lacking. PFTs have evolved recognition mechanisms to bind specific receptors that define their host tropism, although this can be remarkably diverse even within the same family. Here we summarise the salient features of PFTs and highlight where additional research is necessary to fully understand the mechanism of pore formation by members of this diverse group of protein toxins.

Kingella kingae RtxA Cytotoxin in the Context of Other RTX Toxins

The Gram-negative bacterium Kingella kingae is part of the commensal oropharyngeal flora of young children. As detection methods have improved, K. kingae has been increasingly recognized as an emerging invasive pathogen that frequently causes skeletal system infections, bacteremia, and severe forms of infective endocarditis. K. kingae secretes an RtxA cytotoxin, which is involved in the development of clinical infection and belongs to an ever-growing family of cytolytic RTX (Repeats in ToXin) toxins secreted by Gram-negative pathogens. All RTX cytolysins share several characteristic structural features: (i) a hydrophobic pore-forming domain in the N-terminal part of the molecule; (ii) an acylated segment where the activation of the inactive protoxin to the toxin occurs by a co-expressed toxin-activating acyltransferase; (iii) a typical calcium-binding RTX domain in the C-terminal portion of the molecule with the characteristic glycine- and aspartate-rich nonapeptide repeats; and (iv) a C-proximal secretion signal recognized by the type I secretion system. RTX toxins, including RtxA from K. kingae, have been shown to act as highly efficient ‘contact weapons’ that penetrate and permeabilize host cell membranes and thus contribute to the pathogenesis of bacterial infections. RtxA was discovered relatively recently and the knowledge of its biological role remains limited. This review describes the structure and function of RtxA in the context of the most studied RTX toxins, the knowledge of which may contribute to a better understanding of the action of RtxA in the pathogenesis of K. kingae infections.

Human Renal Fibroblasts, but Not Renal Epithelial Cells, Induce IL-1β Release during a Uropathogenic Escherichia coli Infection In Vitro

Understanding how uropathogenic Escherichia coli (UPEC) modulates the immune response in the kidney is essential to prevent UPEC from reaching the bloodstream and causing urosepsis. The purpose of this study was to elucidate if renal fibroblasts can release IL-1β during a UPEC infection and to investigate the mechanism behind the IL-1β release. We found that the UPEC strain CFT073 induced an increased IL-1β and LDH release from renal fibroblasts, but not from renal epithelial cells. The UPEC-induced IL-1β release was found to be NLRP3, caspase-1, caspase-4, ERK 1/2, cathepsin B and serine protease dependent in renal fibroblasts. We also found that the UPEC virulence factor α-hemolysin was necessary for IL-1β release. Conditioned medium from caspase-1, caspase-4 and NLRP3-deficient renal fibroblasts mediated an increased reactive oxygen species production from neutrophils, but reduced UPEC phagocytosis. Taken together, our study demonstrates that renal fibroblasts, but not renal epithelial cells, release IL-1β during a UPEC infection. This suggest that renal fibroblasts are vital immunoreactive cells and not only structural cells that produce and regulate the extracellular matrix.

A previously uncharacterized two-component signaling system in uropathogenic Escherichia coli coordinates protection against host-derived oxidative stress with activation of hemolysin-mediated host cell pyroptosis

Uropathogenic Escherichia coli (UPEC) deploy an array of virulence factors to successfully establish urinary tract infections. Hemolysin is a pore-forming toxin, and its expression correlates with the severity of UPEC infection. Two-component signaling systems (TCSs) are a major mechanism by which bacteria sense environmental cues and respond by initiating adaptive responses. Here, we began this study by characterizing a novel TCS (C3564/C3565, herein renamed orhK/orhR for oxidative resistance and hemolysis kinase/regulator) that is encoded on a UPEC pathogenicity island, using bioinformatic and biochemical approaches. A prevalence analysis indicates that orhK/orhR is highly associated with the UPEC pathotype, and it rarely occurs in other E. coli pathotypes tested. We then demonstrated that OrhK/OrhR directly activates the expression of a putative methionine sulfoxide reductase system (C3566/C3567) and hemolysin (HlyA) in response to host-derived hydrogen peroxide (H₂O₂) exposure. OrhK/OrhR increases UPEC resistance to H₂O₂in vitro and survival in macrophages in cell culture via C3566/C3567. Additionally, OrhK/OrhR mediates hemolysin-induced renal epithelial cell and macrophage death via a pyroptosis pathway. Reducing intracellular H₂O₂ production by a chemical inhibitor impaired OrhK/OrhR-mediated activation of c3566-c3567 and hlyA. We also uncovered that UPEC links the two key virulence traits by cotranscribing the c3566-c3567 and hlyCABD operons. Taken together, our data suggest a paradigm in which a signal transduction system coordinates both bacterial pathogen defensive and offensive traits in the presence of host-derived signals; and this exquisite mechanism likely contributes to hemolysin-induced severe pathological outcomes.

Uropathogenic Escherichia coli (UPEC) is the primary cause of urinary tract infections, and approximately half of UPEC isolates produce a pore-forming toxin, hemolysin. Clinically, hemolysin carriage is associated with severe pathology and symptoms during UPEC infections. However, overexpression of hemolysin can be detrimental to UPEC colonization. Therefore, fine-tuning of hemolysin expression in response to in vivo-relevant signals is critical for optimal UPEC fitness in the urinary tract. In this study, we describe a virulence strategy employed by UPEC, i.e., the bacteria use a two-component signaling (TCS) system to coordinate oxidative stress resistance and hemolysin-mediated pyroptosis of host cells in response to host-derived oxidative signals. The TCS achieves this coordination by cotranscribing genes encoding the oxidative stress resistance and the hemolysin. As a result, UPEC is able to link defense to offense, and this exquisite virulence mechanism likely contributes to UPEC fitness in vivo and hemolysin-induced severe pathological outcomes.

Bis-molybdopterin guanine dinucleotide modulates hemolysin expression under anaerobiosis and contributes to fitness in vivo in uropathogenic Escherichia coli

Uropathogenic Escherichia coli (UPEC) is the primary causative agent of urinary tract infections (UTIs). Successful urinary tract colonization requires appropriate expression of virulence factors in response to host environmental cues, such as limited oxygen and iron availability. Hemolysin is a pore-forming toxin, and its expression correlates with the severity of UPEC infection. Previously, we showed that hemolysin expression is enhanced under anaerobic conditions; however, the genetic basis and regulatory mechanisms involved remain undefined. Here, a transposon-based forward screen identified bis-molybdopterin guanine dinucleotide cofactor (bis-MGD) biosynthesis as an important factor for a full transcription of hemolysin under anaerobiosis but not under aerobiosis. bis-MGD positively influences hemolysin transcription via c3566-c3568, an operon immediately upstream of and cotranscribed with hlyCABD. Furthermore, suppressor mutation analysis identified the nitrogen regulator NtrC as a direct repressor of c3566-c3568-hlyCABD expression, and intact bis-MGD biosynthesis downregulated ntrC expression, thus at least partially explaining the positive role of bis-MGD in modulating hemolysin expression. Finally, bis-MGD is involved in hemolysin-mediated uroepithelial cell death and contributes to the competitive fitness of UPEC in a murine model of UTI. Collectively, our data establish that bis-MGD biosynthesis plays a crucial role in UPEC fitness in vivo, thus providing a potential target for combatting UTIs.

Bacterial RTX toxins and host immunity

PURPOSE OF REVIEW

RTX toxin action often defines the outcome of bacterial infections. Here, we discuss the progress in understanding the impacts of RTX toxin activities on host immunity.

RECENT FINDINGS

Bordetella pertussis CyaA activity paralyzes sentinel phagocytic cells by elevating cellular cAMP levels and blocks differentiation of infiltrating monocytes into bactericidal macrophages, promoting also de-differentiation of resident alveolar macrophages into monocyte-like cells. Vibrio cholerae multifunctional autoprocessing repeats-in-toxins (MARTX), through Rho inactivating and α/β-hydrolase (ABH) domain action blocks mitogen-activated protein kinase signaling in epithelial cells and dampens the inflammatory responses of intestinal epithelia by blocking immune cell recruitment. The action of actin crosslinking effector domain and Ras/Rap1-specific endopeptidase (RRSP) domains of MARTX compromises the phagocytic ability of macrophages. Aggregatibacter actinomycetemcomitans LtxA action triggers neutrophil elastase release into periodontal tissue, compromising the epithelial barrier and promoting bacterial spreads into deeper tissue.

SUMMARY

Action of RTX toxins enables bacterial pathogens to cope with the fierce host immune defenses. RTX toxins often block phagocytosis and bactericidal reactive oxygen species and NO production. Some RTX toxins can reprogram the macrophages to less bactericidal cell types. Autophagy is hijacked for example by the activity of the V. cholerae ABH effector domain of the MARTX protein. Subversion of immune functions by RTX toxins thus promotes bacterial survival and proliferation in the host.

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.

Recurrent Urinary Tract Infections: Unraveling the Complicated Environment of Uncomplicated rUTIs

Urinary tract infections (UTIs) are frequent in humans, affecting the upper and lower urinary tract. Present diagnosis relies on the positive culture of uropathogenic bacteria from urine and clinical markers of inflammation of the urinary tract. The bladder is constantly challenged by adverse environmental stimuli which influence urinary tract physiology, contributing to a dysbiotic environment. Simultaneously, pathogens are primed by environmental stressors such as antibiotics, favoring recurrent UTIs (rUTIs), resulting in chronic illness. Due to different confounders for UTI onset, a greater understanding of the fundamental environmental mechanisms and microbial ecology of the human urinary tract is required. Such advancements could promote the tandem translation of bench and computational studies for precision treatments and clinical management of UTIs. Therefore, there is an urgent need to understand the ecological interactions of the human urogenital microbial communities which precede rUTIs. This review aims to outline the mechanistic aspects of rUTI ecology underlying dysbiosis between both the human microbiome and host physiology which predisposes humans to rUTIs. By assessing the applications of next generation and systems level methods, we also recommend novel approaches to elucidate the systemic consequences of rUTIs which requires an integrated approach for successful treatment. To this end, we will provide an outlook towards the so-called 'uncomplicated environment of UTIs', a holistic and systems view that applies ecological principles to define patient-specific UTIs. This perspective illustrates the need to withdraw from traditional reductionist perspectives in infection biology and instead, a move towards a systems-view revolving around patient-specific pathophysiology during UTIs.

Meningitic Escherichia coli α-hemolysin aggravates blood-brain barrier disruption via targeting TGFβ1-triggered hedgehog signaling

Bacterial meningitis is a life-threatening infectious disease with severe neurological sequelae and a high mortality rate, in which Escherichia coli is one of the primary Gram-negative etiological bacteria. Meningitic E. coli infection is often accompanied by an elevated blood–brain barrier (BBB) permeability. BBB is the structural and functional barrier composed of brain microvascular endothelial cells (BMECs), astrocytes, and pericytes, and we have previously shown that astrocytes-derived TGFβ1 physiologically maintained the BBB permeability by triggering a non-canonical hedgehog signaling in brain microvascular endothelial cells (BMECs). Here, we subsequently demonstrated that meningitic E. coli infection could subvert this intercellular communication within BBB by attenuating TGFBRII/Gli2-mediated such signaling. By high-throughput screening, we identified E. coli α-hemolysin as the critical determinant responsible for this attenuation through Sp1-dependent TGFBRII reduction and triggering Ca²⁺ influx and protein kinase A activation, thus leading to Gli2 suppression. Additionally, the exogenous hedgehog agonist SAG exhibited promising protection against the infection-caused BBB dysfunction. Our work revealed a hedgehog-targeted pathogenic mechanism during meningitic E. coli-caused BBB disruption and suggested that activating hedgehog signaling within BBB could be a potential protective strategy for future therapy of bacterial meningitis.

Genomic Characterization of hlyF-positive Shiga Toxin-Producing Escherichia coli, Italy and the Netherlands, 2000-2019

Shiga toxin–producing Escherichia coli (STEC) O80:H2 has emerged in Europe as a cause of hemolytic uremic syndrome associated with bacteremia. STEC O80:H2 harbors the mosaic plasmid pR444_A, which combines several virulence genes, including hlyF and antimicrobial resistance genes. pR444_A is found in some extraintestinal pathogenic E. coli (ExPEC) strains. We identified and characterized 53 STEC strains with ExPEC-associated virulence genes isolated in Italy and the Netherlands during 2000–2019. The isolates belong to 2 major populations: 1 belongs to sequence type 301 and harbors diverse stx₂ subtypes, the intimin variant eae-ξ, and pO157-like and pR444_A plasmids; 1 consists of strains belonging to various sequence types, some of which lack the pO157 plasmid, the locus of enterocyte effacement, and the antimicrobial resistance–encoding region. Our results showed that STEC strains harboring ExPEC-associated virulence genes can include multiple serotypes and that the pR444_A plasmid can be acquired and mobilized by STEC strains.

UPEC kidney infection triggers neuro-immune communication leading to modulation of local renal inflammation by splenic IFNγ

Bacterial infection results in a veritable cascade of host responses, both local and systemic. To study the initial stages of host-pathogen interaction in living tissue we use spatially-temporally controlled in vivo models. Using this approach, we show here that within 4 h of a uropathogenic Escherichia coli (UPEC) infection in the kidney, an IFNγ response is triggered in the spleen. This rapid infection-mediated inter-organ communication was found to be transmitted via nerve signalling. Bacterial expression of the toxin α-hemolysin directly and indirectly activated sensory neurons, which were identified in the basement membrane of renal tubules. Nerve activation was transmitted via the splenic nerve, inducing upregulation of IFNγ in the marginal zones of the spleen that led to increasing concentrations of IFNγ in the circulation. We found that IFNγ modulated the inflammatory signalling generated by renal epithelia cells in response to UPEC infection. This demonstrates a new concept in the host response to kidney infection; the role of nerves in sensing infection and rapidly triggering a systemic response which can modulate inflammation at the site of infection. The interplay between the nervous and immune systems is an exciting, developing field with the appealing prospect of non-pharmaceutical interventions. Our study identifies an important role for systemic neuro-immune communication in modulating inflammation during the very first hours of a local bacterial infection in vivo.

Sex effects in pyelonephritis

Urinary tract infections (UTIs) are generally considered a disease of women. However, UTIs affect females throughout the lifespan, and certain male populations (including infants and elderly men) are also susceptible. Epidemiologically, pyelonephritis is more common in women but carries increased morbidity when it does occur in men. Among children, high-grade vesicoureteral reflux is a primary risk factor for upper-tract UTI in both sexes. However, among young infants with UTI, girls are outnumbered by boys; risk factors include posterior urethral valves and lack of circumcision. Recent advances in mouse models of UTI reveal sex differences in innate responses to UTI, which vary somewhat depending on the system used. Moreover, male mice and androgenized female mice suffer worse outcomes in experimental pyelonephritis; evidence suggests that androgen exposure may suppress innate control of infection in the urinary tract, but additional androgen effects, as well as non-hormonal sex effects, may yet be specified. Among other intriguing directions, recent experiments raise the hypothesis that the postnatal testosterone surge that occurs in male infants may represent an additional factor driving the higher incidence of UTI in males under 6 months of age. Ongoing work in contemporary models will further illuminate sex- and sex-hormone-specific effects on UTI pathogenesis and immune responses.

Insight Into the Virulence Related Secretion Systems, Fimbriae, and Toxins in O2:K1 Escherichia coli Isolated From Bovine Mastitis

Mastitis remains a major infection of dairy cows and an important issue for the dairy farmers, and Escherichia coli (E. coli) bovine mastitis is a disease of significant economic importance in the dairy industry. Our study identified six isolates belong to phylogroup B2 from 69 bovine mastitis E. coli strains. Except for one serotype O1 strain, all group B2 isolates were identified into serotype O2 and showed significantly higher mortality in the mouse infection than other phylogroups' strains. Genomic analyses and further tests were performed to examine the role of secretion systems, fimbriae, and toxins during the systemic infection of O2:K1 strain BCE049. Two integral T6SS loci and three predicted effectors clusters were found to assemble the functional T6SS complex and deliver diverse toxic effectors to modulate bacterial virulence in the mouse infection model. A total of four T4SS loci were harbored in the BCE049 genome, three of them are encoded in different plasmids, respectively, whereas the last one locates within the bacterial chromosome at FQU84_16715 to FQU84_16760, and was significantly involved in the bacterial pathogenicity. Numerous predicted pilus biosynthesis gene loci were found in the BCE049 genome, whereas most of them lost long fragments encoding key genes for the pili assembly. Unexpectedly, a type IV pilus gene locus locating at FQU84_01405 to FQU84_01335 in the plasmid 2, was found to be required for the full virulence of mastitis strain BCE049. It should be noted that a genetic neighborhood inserted with diverse genes is encoded by the plasmid 1, which harbors three prominent toxins including β-hemolysin, cytotoxic necrotizing factor 2 and cytolethal distending toxin type III. Consequent studies verified that these toxins significantly contributed to the bacterial pathogenicity. These findings provide a molecular blueprint for understanding the underlying mechanisms employed by the bovine mastitis E. coli to colonize in host and cause systemic infection.

Uropathogenic Escherichia coli Virulence Factor α-Hemolysin Reduces Histone Acetylation to Inhibit Expression of Proinflammatory Cytokine Genes

Urinary tract infections are common and costly diseases affecting millions of people. Uropathogenic Escherichia coli (UPEC) is a primary cause of these infections and has developed multiple strategies to avoid the host immune response. Here, we dissected the molecular mechanisms underpinning UPEC inhibition of inflammatory cytokine in vitro and in vivo. We found that UPEC infection simulates nuclear factor-κB activation but does not result in transcription of cytokine genes. Instead, UPEC-mediated suppression of the metabolic enzyme ATP citrate lyase results in decreased acetyl-CoA levels, leading to reduced H3K9 histone acetylation in the promotor region of CXCL8. These effects were dependent on the UPEC virulence factor α-hemolysin and were reversed by exogenous acetate. In a murine cystitis model, prior acetate supplementation rapidly resolved UPEC-elicited immune responses and improved tissue recovery. Thus, upon infection, UPEC rearranges host cell metabolism to induce chromatin remodeling processes that subvert expression of host innate immune response genes.

Activation of NLRP3 by uropathogenic Escherichia coli is associated with IL-1β release and regulation of antimicrobial properties in human neutrophils

The NLRP3 inflammasome and IL-1β have recently been linked to the severity of uropathogenic Escherichia coli (UPEC)-mediated urinary tract infection (UTI). However, not much is known about the contribution of NLRP3 to the antimicrobial properties of neutrophils and the release of IL-1β during UPEC infection. The purpose of this study was to elucidate the mechanisms behind UPEC-induced IL-1β release from human neutrophils, and to investigate the contribution of the NLRP3 inflammasome in neutrophil-mediated inhibition of UPEC growth. We found that the UPEC strain CFT073 increased the expression of NLRP3 and increased caspase-1 activation and IL-1β release from human neutrophils. The IL-1β release was mediated by the NLRP3 inflammasome and by serine proteases in an NF-κB-and cathepsin B-dependent manner. The UPEC virulence factors α-hemolysin, type-1 fimbriae and p-fimbriae were all shown to contribute to UPEC mediated IL-1β release from neutrophils. Furthermore, inhibition of caspase-1 and NLRP3 activation increased neutrophil ROS-production, phagocytosis and the ability of neutrophils to suppress UPEC growth. In conclusion, this study demonstrates that UPEC can induce NLRP3 and serine protease-dependent release of IL-1β from human neutrophils and that NLRP3 and caspase-1 can regulate the antimicrobial activity of human neutrophils against UPEC.

Pathogenicity Factors of Genomic Islands in Intestinal and Extraintestinal Escherichia coli

Escherichia coli is a versatile bacterial species that includes both harmless commensal strains and pathogenic strains found in the gastrointestinal tract in humans and warm-blooded animals. The growing amount of DNA sequence information generated in the era of "genomics" has helped to increase our understanding of the factors and mechanisms involved in the diversification of this bacterial species. The pathogenic side of E. coli that is afforded through horizontal transfers of genes encoding virulence factors enables this bacterium to become a highly diverse and adapted pathogen that is responsible for intestinal or extraintestinal diseases in humans and animals. Many of the accessory genes acquired by horizontal transfers form syntenic blocks and are recognized as genomic islands (GIs). These genomic regions contribute to the rapid evolution, diversification and adaptation of E. coli variants because they are frequently subject to rearrangements, excision and transfer, as well as to further acquisition of additional DNA. Here, we review a subgroup of GIs from E. coli termed pathogenicity islands (PAIs), a concept defined in the late 1980s by Jörg Hacker and colleagues in Werner Goebel's group at the University of Würzburg, Würzburg, Germany. As with other GIs, the PAIs comprise large genomic regions that differ from the rest of the genome by their G + C content, by their typical insertion within transfer RNA genes, and by their harboring of direct repeats (at their ends), integrase determinants, or other mobility loci. The hallmark of PAIs is their contribution to the emergence of virulent bacteria and to the development of intestinal and extraintestinal diseases. This review summarizes the current knowledge on the structure and functional features of PAIs, on PAI-encoded E. coli pathogenicity factors and on the role of PAIs in host-pathogen interactions.

The Serine Protease Autotransporters TagB, TagC, and Sha from Extraintestinal Pathogenic Escherichia coli Are Internalized by Human Bladder Epithelial Cells and Cause Actin Cytoskeletal Disruption

TagB, TagC (tandem autotransporter genes B and C), and Sha (Serine-protease hemagglutinin autotransporter) are recently described members of the SPATE (serine protease autotransporters of Enterobacteriaceae) family. These SPATEs can cause cytopathic effects on bladder cells and contribute to urinary tract infection in a mouse model. Bladder epithelial cells form an important barrier in the urinary tract. Some SPATEs produced by pathogenic E. coli are known to breach the bladder epithelium. The capacity of these newly described SPATEs to alter bladder epithelial cells and the role of the serine protease active site were investigated. All three SPATE proteins were internalized by bladder epithelial cells and altered the distribution of actin cytoskeleton. Sha and TagC were also shown to degrade mucin and gelatin respectively. Inactivation of the serine catalytic site in each of these SPATEs did not affect secretion of the SPATEs from bacterial cells, but abrogated entry into epithelial cells, cytotoxicity, and proteolytic activity. Thus, our results show that the serine catalytic triad of these proteins is required for internalization in host cells, actin disruption, and degradation of host substrates such as mucin and gelatin.

Oral and intestinal bacterial exotoxins: Potential linked to carcinogenesis

Growing evidence suggests that imbalances in resident microbes (dysbiosis) can promote chronic inflammation, immune-subversion, and production of carcinogenic metabolites, thus leading to neoplasia. Yet, evidence to support a direct link of individual bacteria species to human sporadic cancer is still limited. This chapter focuses on several emerging bacterial toxins that have recently been characterized for their potential oncogenic properties toward human orodigestive cancer and the presence of which in human tissue samples has been documented. These include cytolethal distending toxins produced by various members of gamma and epsilon Proteobacteria, Dentilisin from mammalian oral Treponema, Pasteurella multocida toxin, two Fusobacterial toxins, FadA and Fap2, Bacteroides fragilis toxin, colibactin, cytotoxic necrotizing factors and α-hemolysin from Escherichia coli, and Salmonella enterica AvrA. It was clear that these bacterial toxins have biological activities to induce several hallmarks of cancer. Some toxins directly interact with DNA or chromosomes leading to their breakdowns, causing mutations and genome instability, and others modulate cell proliferation, replication and death and facilitate immune evasion and tumor invasion, prying specific oncogene and tumor suppressor pathways, such as p53 and β-catenin/Wnt. In addition, most bacterial toxins control tumor-promoting inflammation in complex and diverse mechanisms. Despite growing laboratory evidence to support oncogenic potential of selected bacterial toxins, we need more direct evidence from human studies and mechanistic data from physiologically relevant experimental animal models, which can reflect chronic infection in vivo, as well as take bacterial-bacterial interactions among microbiome into consideration.

Role of luxS in immune evasion and pathogenicity of piscine Streptococcus agalactiae is not dependent on autoinducer-2

luxS-mediated autoinducer 2 (AI-2)-dependent quorum sensing (QS) has been demonstrated to affect many bacterial phenotypes, including virulence. Streptococcus agalactiae harbors a functional luxS gene required for the biosynthesis of AI-2. In this study, we investigated the regulation effect and mechanism of the luxS/AI-2 QS system in the pathogenicity of the piscine S. agalactiae strain GD201008-001. We found that inactivation of luxS caused a marked decrease in biofilm formation, hemolytic activity, antiphagocytosis and intracellular survival of S. agalactiae. Except for hemolytic activity, the altered phenotypes due to the luxS deletion were AI-2-independent. Further investigation indicated that high levels of the proinflammatory cytokines IL-1β and IL-6 could be induced in macrophages co-incubated with the luxS deletion mutant and synthetic AI-2, single or combined. Also, the results of tilapia infection showed that inactivation of luxS significantly decreased the virulence of S. agalactiae but upregulated the expression of cytokines in spleens and brains. Increased proinflammatory effects of the luxS mutant were restored in the luxS complemented strain but could not be restored by AI-2 addition. All the findings suggest that luxS is involved in virulence-associated phenotypes and immunological evasion of S. agalactiae, and furthermore, this involvement is mostly AI-2-independent. This study will provide valuable insights into our understanding of the role of the LuxS/AI-2 QS system in the pathogenesis of S. agalactiae.

Reaching the End of the Line: Urinary Tract Infections

Urinary tract infections (UTIs) cause a substantial health care burden. UTIs (i) are most often caused by uropathogenic Escherichia coli (UPEC), (ii) primarily affect otherwise healthy females (50% of women will have a UTI), (iii) are associated with significant morbidity and economic impact, (iv) can become chronic, and (v) are highly recurrent. A history of UTI is a significant risk factor for a recurrent UTI (rUTI). In otherwise healthy women, an acute UTI leads to a 25 to 50% chance of rUTI within months of the initial infection. Interestingly, rUTIs are commonly caused by the same strain of E. coli that led to the initial infection, arguing that there exist host-associated reservoirs, like the gastrointestinal tract and underlying bladder tissue, that can seed rUTIs. Additionally, catheter-associated UTIs (CAUTI), caused by Enterococcus and Staphylococcus as well as UPEC, represent a major health care concern. The host's response of depositing fibrinogen at the site of infection has been found to be critical to establishing CAUTI. The Drug Resistance Index, an evaluation of antibiotic resistance, indicates that UTIs have become increasingly difficult to treat since the mid-2000s. Thus, UTIs are a "canary in the coal mine," warning of the possibility of a return to the preantibiotic era, where some common infections are untreatable with available antibiotics. Numerous alternative strategies for both the prevention and treatment of UTIs are being pursued, with a focus on the development of vaccines and small-molecule inhibitors targeting virulence factors, in the hopes of reducing the burden of urogenital tract infections in an antibiotic-sparing manner.

Alpha-hemolysin of uropathogenic Escherichia coli induces GM-CSF-mediated acute kidney injury

Uropathogenic Escherichia coli (UPEC) is the leading cause of urinary tract infections (UTIs), inducing acute pyelonephritis and may result in permanent renal scarring and failure. Alpha-hemolysin (HlyA), a key UPEC toxin, causes serious tissue damage; however, the mechanism through which HlyA induces kidney injury remains unclear. In the present study, granulocyte-macrophage colony-stimulating factor (GM-CSF) secreted by renal epithelial cells was upregulated by HlyA in vitro and in vivo, which induced M1 macrophage accumulation in kidney, and ADAM10 was found involved in HlyA-induced GM-CSF. Macrophage elimination or GM-CSF neutralization protected against acute kidney injury in mice, and increased GM-CSF was detected in urine of patients infected by hlyA-positive UPEC. In addition, HlyA was found to promote UPEC invasion into renal epithelial cells by interacting with Nectin-2 in vitro. However, HlyA did not affect bacterial titers during acute kidney infections, and HlyA-induced invasion did not contribute to GM-CSF upregulation in vitro, which indicate that HlyA-induced GM-CSF is independent of bacteria invasion. The role of GM-CSF in HlyA-mediated kidney injury may lead to novel strategies to treat acute pyelonephritis.

Bacterial Manipulation of Wnt Signaling: A Host-Pathogen Tug-of-Wnt

The host-pathogen interface is a crucial battleground during bacterial infection in which host defenses are met with an array of bacterial counter-mechanisms whereby the invader aims to make the host environment more favorable to survival and dissemination. Interestingly, the eukaryotic Wnt signaling pathway has emerged as a key player in the host and pathogen tug-of-war. Although studied for decades as a regulator of embryogenesis, stem cell maintenance, bone formation, and organogenesis, Wnt signaling has recently been shown to control processes related to bacterial infection in the human host. Wnt signaling pathways contribute to cell cycle control, cytoskeleton reorganization during phagocytosis and cell migration, autophagy, apoptosis, and a number of inflammation-related events. Unsurprisingly, bacterial pathogens have evolved strategies to manipulate these Wnt-associated processes in order to enhance infection and survival within the human host. In this review, we examine the different ways human bacterial pathogens with distinct host cell tropisms and lifestyles exploit Wnt signaling for infection and address the potential of harnessing Wnt-related mechanisms to combat infectious disease.

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.

The Extracellular Domain of the β2 Integrin β Subunit (CD18) Is Sufficient for Escherichia coli Hemolysin and Aggregatibacter actinomycetemcomitans Leukotoxin Cytotoxic Activity

Urinary tract infections are one of the most common bacterial infections worldwide. Uropathogenic Escherichia coli strains are responsible for more than 80% of community-acquired urinary tract infections. Although we have known for nearly a century that severe infections stemming from urinary tract infections, including kidney or bloodstream infections are associated with expression of a toxin, hemolysin, from uropathogenic Escherichia coli, how hemolysin functions to enhance virulence is unknown. Our research defines the interaction of hemolysin with the β₂ integrin, a human white cell adhesion molecule, as a potential therapeutic target during urinary tract infections. The E. coli hemolysin is the prototype for a toxin family (RTX family) produced by a wide array of human and animal pathogens. Our work extends to the identification and characterization of the receptor for an additional member of the RTX family, suggesting that this interaction may be broadly conserved throughout the RTX toxin family.

The Escherichia coli hemolysin (HlyA) is a pore-forming exotoxin associated with severe complications of human urinary tract infections. HlyA is the prototype of the repeats-in-toxin (RTX) family, which includes LtxA from Aggregatibacter actinomycetemcomitans, a periodontal pathogen. The existence and requirement for a host cell receptor for these toxins are controversial. We performed an unbiased forward genetic selection in a mutant library of human monocytic cells, U-937, for host factors involved in HlyA cytotoxicity. The top candidate was the β₂ integrin β subunit. Δβ₂ cell lines are approximately 100-fold more resistant than wild-type U-937 cells to HlyA, but remain sensitive to HlyA at high concentrations. Similarly, Δβ₂ cells are more resistant than wild-type U-937 cells to LtxA, as Δβ₂ cells remain LtxA resistant even at >1,000-fold-higher concentrations of the toxin. Loss of any single β₂ integrin α subunit, or even all four α subunits together, does not confer resistance to HlyA. HlyA and LtxA bind to the β₂ subunit, but not to α_L, α_M, or α_X in far-Western blots. Genetic complementation of Δβ₂ cells with either β₂ or β₂ with a cytoplasmic tail deletion restores HlyA and LtxA sensitivity, suggesting that β₂ integrin signaling is not required for cytotoxicity. Finally, β₂ mutations do not alter sensitivity to unrelated pore-forming toxins, as wild-type or Δβ₂ cells are equally sensitive to Staphylococcus aureus α-toxin and Proteus mirabilis HpmA. Our studies show two RTX toxins use the β₂ integrin β subunit alone to facilitate cytotoxicity, but downstream integrin signaling is dispensable.

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.

Protective vascular coagulation in response to bacterial infection of the kidney is regulated by bacterial lipid A and host CD147

Bacterial infection of the kidney leads to a rapid cascade of host protective responses, many of which are still poorly understood. We have previously shown that following kidney infection with uropathogenic Escherichia coli (UPEC), vascular coagulation is quickly initiated in local perivascular capillaries that protects the host from progressing from a local infection to systemic sepsis. The signaling mechanisms behind this response have not however been described. In this study, we use a number of in vitro and in vivo techniques, including intravital microscopy, to identify two previously unrecognized components influencing this protective coagulation response. The acylation state of the Lipid A of UPEC lipopolysaccharide (LPS) is shown to alter the kinetics of local coagulation onset in vivo. We also identify epithelial CD147 as a potential host factor influencing infection-mediated coagulation. CD147 is expressed by renal proximal epithelial cells infected with UPEC, contingent to bacterial expression of the α-hemolysin toxin. The epithelial CD147 subsequently can activate tissue factor on endothelial cells, a primary step in the coagulation cascade. This study emphasizes the rapid, multifaceted response of the kidney tissue to bacterial infection and the interplay between host and pathogen during the early hours of renal infection.