Characterization of the StcE protease activity of Escherichia coli O157:H7

Targeting virulence of resistant Escherichia coli by the FDA-approved drugs sitagliptin and nitazoxanide as an alternative antimicrobial approach

The spread of multidrug-resistant Escherichia coli in healthcare facilities is a global challenge. Hospital-acquired infections produced by Escherichia coli include gastrointestinal, blood-borne, urinary tract, surgical sites, and neonatal infections. Therefore, novel approaches are needed to deal with this pathogen and its rising resistance. The concept of attenuating virulence factors is an alternative strategy that might lead to low levels of resistance and combat this pathogen. A sub-inhibitory concentration (¼ MIC) of sitagliptin and nitazoxanide was used for phenotypic assessments of Escherichia coli virulence factors such as biofilm production, swimming motility, serum resistance, and protease production. Moreover, qRT-PCR was used to determine the impact of sub-MIC of the tested drugs on the relative expression levels of papC, fimH, fliC, kpsMTII, ompT_m, and stcE genes encoding virulence factors in Escherichia coli. Also, an in vivo model was conducted as a confirmatory test. Phenotypically, our findings demonstrated that the tested strains showed a significant decrease in all the tested virulence factors. Moreover, the genotypic results showed a significant downregulation in the relative expression levels of all the tested genes. Besides, the examined drugs were found to be effective in protecting mice against Escherichia coli pathogenesis. Sitagliptin and nitazoxanide exhibited strong anti-virulence activities against Escherichia coli. In addition, it is recommended that they might function as adjuvant in the management of Escherichia coli infections with either conventional antimicrobial agents or alone as alternative treatment measures.

The Promising Effect of Ascorbic Acid and Paracetamol as Anti-Biofilm and Anti-Virulence Agents against Resistant Escherichia coli

Escherichia coli is a major cause of serious infections, with antibiotic resistance rendering many treatments ineffective. Hence, novel strategies to combat this pathogen are needed. Anti-virulence therapy is a promising new approach for the subsequent era. Recent research has examined the impact of sub-inhibitory doses of ascorbic acid and paracetamol on Escherichia coli virulence factors. This study evaluated biofilm formation, protease production, motility behavior, serum resistance, expression of virulence-regulating genes (using RT-PCR), and survival rates in a mouse model. Ascorbic acid significantly reduced biofilm formation, protease production, motility, and serum resistance from 100% in untreated isolates to 22-89%, 10-89%, 2-57%, and 31-35% in treated isolates, respectively. Paracetamol also reduced these factors from 100% in untreated isolates to 16-76%, 1-43%, 16-38%, and 31-35%, respectively. Both drugs significantly down-regulated virulence-regulating genes papC, fimH, ompT_m, stcE, fliC, and kpsMTII. Mice treated with these drugs had a 100% survival rate compared with 60% in the positive control group control inoculated with untreated bacteria. This study highlights the potential of ascorbic acid and paracetamol as anti-virulence agents, suggesting their use as adjunct therapies alongside conventional antimicrobials or as alternative treatments for resistant Escherichia coli infections.

Emerging Aeromonas enteric infections: their association with inflammatory bowel disease and novel pathogenic mechanisms

Aeromonas species are emerging human enteric pathogens. This study examines the isolation of Aeromonas and other enteric bacterial pathogens from patients with and without inflammatory bowel disease (IBD). This study also investigates the intestinal epithelial pathogenic mechanisms of Aeromonas veronii. The isolation rates of seven enteric bacterial pathogens from 2,279 patients with IBD and 373,276 non-IBD patients were compared. An A. veronii strain (AS1) isolated from intestinal biopsies of a patient with IBD was used for pathogenic mechanism investigation, and Escherichia coli K12 was used as a bacterial control. HT-29 cells were used as a model of human intestinal epithelium. A significantly higher isolation of Aeromonas species was found in patients with IBD as compared to non-IBD patients (P = 0.0001, odds ratio = 2.11). A. veronii upregulated 177 inflammatory genes and downregulated 52 protein-coding genes affecting chromatin assembly, multiple small nuclear RNAs, multiple nucleolar RNAs, and 55 cytoplasmic tRNAs in HT-29 cells. These downregulation effects were unique to A. veronii and not observed in HT-29 cells infected with E. coli K12. A. veronii induced intestinal epithelial apoptosis involving the intrinsic pathway. A. veronii caused epithelial microvilli shortening and damage and epithelial production of IL-8. In conclusion, this study for the first time reports the association between IBD and Aeromonas enteric infection detected by bacterial cultivation. This study also reports that A. veronii damages intestinal epithelial cells via multiple mechanisms, of which the downregulating cytoplasmic tRNA, small nuclear RNA, and small nucleolar RNA are novel bacterial pathogenic mechanisms. IMPORTANCE This study for the first time reports the association between inflammatory bowel disease (IBD) and Aeromonas enteric infection detected by bacterial pathogen cultivation, highlighting the need of clinical and public health attention. The finding that patients with IBD are more susceptible to Aeromonas enteric infection suggests that detection of Aeromonas enteric infection should be routinely performed for the diagnosis and treatment of IBD. This study also reports novel bacterial pathogenic mechanisms employed by Aeromonas veronii. Through comparative transcriptomic analysis and other techniques, this study revealed the pathogenic mechanisms by which A. veronii causes damage to intestinal epithelial cells. Among the various pathogenic mechanisms identified, the downregulating tRNA, small nuclear and nucleolar RNAs in human intestinal epithelial cells are novel bacterial pathogenic mechanisms.

A mucin-regulated adhesin determines the spatial organization and inflammatory character of a bacterial symbiont in the vertebrate gut

In a healthy gut, microbes are often aggregated with host mucus, yet the molecular basis for this organization and its impact on intestinal health are unclear. Mucus is a viscous physical barrier separating resident microbes from epithelia, but it also provides glycan cues that regulate microbial behaviors. Here, we describe a mucin-sensing pathway in an Aeromonas symbiont of zebrafish, Aer01. In response to the mucin-associated glycan N-acetylglucosamine, a sensor kinase regulates the expression of an aggregation-promoting adhesin we named MbpA. Upon MbpA disruption, Aer01 colonizes to normal levels but is largely planktonic and more pro-inflammatory. Increasing cell surface MbpA rescues these traits. MbpA-like adhesins are common in human-associated bacteria, and the expression of an Akkermansia muciniphila MbpA-like adhesin in MbpA-deficient Aer01 restores lumenal aggregation and reverses its pro-inflammatory character. Our work demonstrates how resident bacteria use mucin glycans to modulate behaviors congruent with host health.

Distinct Molecular Features of NleG Type 3 Secreted Effectors Allow for Different Roles during Citrobacter rodentium Infection in Mice

The NleGs are the largest family of type 3 secreted effectors in attaching and effacing (A/E) pathogens, such as enterohemorrhagic Escherichia coli (EHEC), enteropathogenic E. coli, and Citrobacter rodentium. NleG effectors contain a conserved C-terminal U-box domain acting as a ubiquitin protein ligase and target host proteins via a variable N-terminal portion. The specific roles of these effectors during infection remain uncertain. Here, we demonstrate that the three NleG effectors-NleG1Cr, NleG7Cr, and NleG8Cr-encoded by C. rodentium DBS100 play distinct roles during infection in mice. Using individual nleGCr knockout strains, we show that NleG7Cr contributes to bacterial survival during enteric infection while NleG1Cr promotes the expression of diarrheal symptoms and NleG8Cr contributes to accelerated lethality in susceptible mice. Furthermore, the NleG8Cr effector contains a C-terminal PDZ domain binding motif that enables interaction with the host protein GOPC. Both the PDZ domain binding motif and the ability to engage with host ubiquitination machinery via the intact U-box domain proved to be necessary for NleG8Cr function, contributing to the observed phenotype during infection. We also establish that the PTZ binding motif in the EHEC NleG8 (NleG8Ec) effector, which shares 60% identity with NleG8Cr, is engaged in interactions with human GOPC. The crystal structure of the NleG8Ec C-terminal peptide in complex with the GOPC PDZ domain, determined to 1.85 Å, revealed a conserved interaction mode similar to that observed between GOPC and eukaryotic PDZ domain binding motifs. Despite these common features, nleG8Ec does not complement the ΔnleG8Cr phenotype during infection, revealing functional diversification between these NleG effectors.

The emerging roles of bacterial proteases in intestinal diseases

Proteases are an evolutionarily conserved family of enzymes that degrade peptide bonds and have been implicated in several common gastrointestinal (GI) diseases. Although luminal proteolytic activity is important for maintenance of homeostasis and health, the current review describes recent advances in our understanding of how overactivity of luminal proteases contributes to the pathophysiology of celiac disease, irritable bowel syndrome, inflammatory bowel disease and GI infections. Luminal proteases, many of which are produced by the microbiota, can modulate the immunogenicity of dietary antigens, reduce mucosal barrier function and activate pro-inflammatory and pro-nociceptive host signaling. Increased proteolytic activity has been ascribed to both increases in protease production and decreases in inhibitors of luminal proteases. With the identification of strains of bacteria that are important sources of proteases and their inhibitors, the stage is set to develop drug or microbial therapies to restore protease balance and alleviate disease.

Deciphering O-glycoprotease substrate preferences with O-Pair Search

O-Glycoproteases are an emerging class of enzymes that selectively digest glycoproteins at positions decorated with specific O-linked glycans. O-Glycoprotease substrates range from any O-glycoprotein (albeit with specific O-glycan modifications) to only glycoproteins harboring specific O-glycosylated sequence motifs, such as those found in mucin domains. Their utility for multiple glycoproteomic applications is driving the search to both discover new O-glycoproteases and to understand how structural features of characterized O-glycoproteases influence their substrate specificities. One challenge of defining O-glycoprotease specificity restraints is the need to characterize O-glycopeptides with site-specific analysis of O-glycosites. Here, we demonstrate how O-Pair Search, a recently developed O-glycopeptide-centric identification platform that enables rapid searches and confident O-glycosite localization, can be used to determine substrate specificities of various O-glycoproteases de novo from LC-MS/MS data of O-glycopeptides. Using secreted protease of C1 esterase inhibitor (StcE) from enterohemorrhagic Escherichia coli and O-endoprotease OgpA from Akkermansia mucinophila, we explore numerous settings that effect O-glycopeptide identification and show how non-specific and semi-tryptic searches of O-glycopeptide data can produce candidate cleavage motifs. These putative motifs can be further used to define new protease cleavage settings that lower search times and improve O-glycopeptide identifications. We use this platform to generate a consensus motif for the recently characterized immunomodulating metalloprotease (IMPa) from Pseudomonas aeruginosa and show that IMPa is a favorable O-glycoprotease for characterizing densely O-glycosylated mucin-domain glycoproteins.

Revealing the human mucinome

Mucin domains are densely O-glycosylated modular protein domains found in various extracellular and transmembrane proteins. Mucin-domain glycoproteins play important roles in many human diseases, such as cancer and cystic fibrosis, but the scope of the mucinome remains poorly defined. Recently, we characterized a bacterial O-glycoprotease, StcE, and demonstrated that an inactive point mutant retains binding selectivity for mucin-domain glycoproteins. In this work, we leverage inactive StcE to selectively enrich and identify mucin-domain glycoproteins from complex samples like cell lysate and crude ovarian cancer patient ascites fluid. Our enrichment strategy is further aided by an algorithm to assign confidence to mucin-domain glycoprotein identifications. This mucinomics platform facilitates detection of hundreds of glycopeptides from mucin domains and highly overlapping populations of mucin-domain glycoproteins from ovarian cancer patients. Ultimately, we demonstrate our mucinomics approach can reveal key molecular signatures of cancer from in vitro and ex vivo sources.

Mucin-domain glycoproteins are densely O-glycosylated proteins with unique secondary structure that imparts a large influence on cellular environments. Here, the authors develop a technique to selectively enrich and characterize mucin-domain glycoproteins from cell lysate and patient biofluids.

A Mucin-Deficient Ocular Surface Mimetic Platform for Interrogating Drug Effects on Biolubrication, Antiadhesion Properties, and Barrier Functionality

Dry eye disease (DED) affects more than 100 million people worldwide, causing significant patient discomfort and imposing a multi-billion-dollar burden on global health care systems. In DED patients, the natural biolubrication process that facilitates pain-free blinking goes awry due to an imbalance of lipids, aqueous medium, and mucins in the tear film, resulting in ocular surface damage. Identifying strategies to reduce adhesion and shear stresses between the ocular surface and the conjunctival cells lining the inside of the eyelid during blink cycles is a promising approach to improve the signs and symptoms of DED. However, current preclinical models for screening ocular lubricants rely on scarce, heterogeneous tissue samples or model substrates that do not capture the complex biochemical and biophysical cues present at the ocular surface. To recapitulate the hierarchical architecture and phenotype of the ocular interface for preclinical drug screening, we developed an in vitro mucin-deficient DED model platform that mimics the complexity of the ocular interface and investigated its utility in biolubrication, antiadhesion, and barrier protection studies using recombinant human lubricin, a promising investigational therapy for DED. The biomimetic platform recapitulated the pathological changes in biolubrication, adhesion, and barrier functionality often observed in mucin-deficient DED patients and demonstrated that recombinant human lubricin can reverse the damage induced by mucin loss in a dose- and conformation-dependent manner. Taken together, these results highlight the potential of the platform─and recombinant human lubricin─in advancing the standard of care for mucin-deficient DED patients.

Mucin-Like Glycoproteins Modulate Interfacial Properties of a Mimetic Ocular Epithelial Surface

Dry eye disease (DED) has high personal and societal costs, but its pathology remains elusive due to intertwined biophysical and biochemical processes at the ocular surface. Specifically, mucin deficiency is reported in a subset of DED patients, but its effects on ocular interfacial properties remain unclear. Herein a novel in vitro mucin-deficient mimetic ocular surface (Mu-DeMOS) with a controllable amount of membrane-tethered mucin molecules is developed to represent the diseased ocular surfaces. Contact angle goniometry on mimetic ocular surfaces reveals that high surface roughness, but not the presence of hydrophilic mucin molecules, delivers constant hydration over native ocular surface epithelia. Live-cell rheometry confirms that the presence of mucin-like glycoproteins on ocular epithelial cells reduces shear adhesive strength at cellular interfaces. Together, optimal surface roughness and surface chemistry facilitate sustainable lubrication for healthy ocular surfaces, while an imbalance between them contributes to lubrication-related dysfunction at diseased ocular epithelial surfaces. Furthermore, the restoration of low adhesive strength at Mu-DeMOS interfaces through a mucin-like glycoprotein, recombinant human lubricin, suggests that increased frictional damage at mucin-deficient cellular surfaces may be reversible. More broadly, these results demonstrate that Mu-DeMOS is a promising platform for drug screening assays and fundamental studies on ocular physiology.

Display of the human mucinome with defined O-glycans by gene engineered cells

Mucins are a large family of heavily O-glycosylated proteins that cover all mucosal surfaces and constitute the major macromolecules in most body fluids. Mucins are primarily defined by their variable tandem repeat (TR) domains that are densely decorated with different O-glycan structures in distinct patterns, and these arguably convey much of the informational content of mucins. Here, we develop a cell-based platform for the display and production of human TR O-glycodomains (~200 amino acids) with tunable structures and patterns of O-glycans using membrane-bound and secreted reporters expressed in glycoengineered HEK293 cells. Availability of defined mucin TR O-glycodomains advances experimental studies into the versatile role of mucins at the interface with pathogenic microorganisms and the microbiome, and sparks new strategies for molecular dissection of specific roles of adhesins, glycoside hydrolases, glycopeptidases, viruses and other interactions with mucin TRs as highlighted by examples.

The Glycoprotease CpaA Secreted by Medically Relevant Acinetobacter Species Targets Multiple O-Linked Host Glycoproteins

CpaA is a glycoprotease expressed by members of the Acinetobacter baumannii-calcoaceticus complex, and it is the first bona fide secreted virulence factor identified in these species. Here, we show that CpaA cleaves multiple targets precisely at O-glycosylation sites preceded by a Pro residue. This feature, together with the observation that sialic acid does not impact CpaA activity, makes this enzyme an attractive tool for the analysis of O-linked human protein for biotechnical and diagnostic purposes. Previous work identified proteins involved in blood coagulation as targets of CpaA. Our work broadens the set of targets of CpaA, pointing toward additional roles in bacterium-host interactions. We propose that CpaA belongs to an expanding class of functionally defined glycoproteases that targets multiple O-linked host glycoproteins.

Glycans decorate proteins and affect their biological function, including protection against proteolytic degradation. However, pathogenic, and commensal bacteria have evolved specific glycoproteases that overcome the steric impediment posed by carbohydrates, cleaving glycoproteins precisely at their glycosylation site(s). Medically relevant Acinetobacter strains employ their type II secretion system (T2SS) to secrete the glycoprotease CpaA, which contributes to virulence. Previously, CpaA was shown to cleave two O-linked glycoproteins, factors V and XII, leading to reduced blood coagulation. In this work, we show that CpaA cleaves a broader range of O-linked human glycoproteins, including several glycoproteins involved in complement activation, such as CD55 and CD46. However, only CD55 was removed from the cell surface, while CD46 remained unaltered during the Acinetobacter nosocomialis infection assay. We show that CpaA has a unique consensus target sequence that consists of a glycosylated serine or threonine residue after a proline residue (P-S/T), and its activity is not affected by sialic acids. Molecular modeling and mutagenesis analysis of CpaA suggest that the indole ring of Trp493 and the ring of the Pro residue in the substrate form a key interaction that contributes to CpaA sequence selectivity. Similar bacterial glycoproteases have recently gained attention as tools for proteomic analysis of human glycoproteins, and CpaA appears to be a robust and attractive new component of the glycoproteomics toolbox. Combined, our work provides insight into the function and possible application of CpaA, a member of a widespread class of broad-spectrum bacterial glycoproteases involved in host-pathogen interactions.

High-resolution characterisation of ESBL/pAmpC-producing Escherichia coli isolated from the broiler production pyramid

The presence of extended-spectrum β-lactamase (ESBL) or plasmid-mediated AmpC β-lactamase (pAmpC)-producing Escherichia coli (ESBL/pAmpC-EC) in livestock is a public health risk given the likelihood of their transmission to humans via the food chain. We conducted whole genome sequencing on 100 ESBL/pAmpC-EC isolated from the broiler production to explore their resistance and virulence gene repertoire, characterise their plasmids and identify transmission events derived from their phylogeny. Sequenced isolates carried resistance genes to four antimicrobial classes in addition to cephalosporins. Virulence gene analysis assigned the majority of ESBL/pAmpC-EC to defined pathotypes. In the complex genetic background of ESBL/pAmpC-EC, clusters of closely related isolates from various production stages were identified and indicated clonal transmission. Phylogenetic comparison with publicly available genomes suggested that previously uncommon ESBL/pAmpC-EC lineages could emerge in poultry, while others might contribute to the maintenance and dissemination of ESBL/pAmpC genes in broilers. The majority of isolates from diverse E. coli lineages shared four dominant plasmids (IncK2, IncI1, IncX3 and IncFIB/FII) with identical ESBL/pAmpC gene insertion sites. These plasmids have been previously reported in diverse hosts, including humans. Our findings underline the importance of specific plasmid groups in the dissemination of cephalosporin resistance genes within the broiler industry and across different reservoirs.

Experimental models to study intestinal microbes–mucus interactions in health and disease

A close symbiotic relationship exists between the intestinal microbiota and its host. A critical component of gut homeostasis is the presence of a mucus layer covering the gastrointestinal tract. Mucus is a viscoelastic gel at the interface between the luminal content and the host tissue that provides a habitat to the gut microbiota and protects the intestinal epithelium. The review starts by setting up the biological context underpinning the need for experimental models to study gut bacteria-mucus interactions in the digestive environment. We provide an overview of the structure and function of intestinal mucus and mucins, their interactions with intestinal bacteria (including commensal, probiotics and pathogenic microorganisms) and their role in modulating health and disease states. We then describe the characteristics and potentials of experimental models currently available to study the mechanisms underpinning the interaction of mucus with gut microbes, including in vitro, ex vivo and in vivo models. We then discuss the limitations and challenges facing this field of research.

The mucin-selective protease StcE enables molecular and functional analysis of human cancer-associated mucins

Mucin domains are densely O-glycosylated modular protein domains that are found in a wide variety of cell surface and secreted proteins. Mucin-domain glycoproteins are known to be key players in a host of human diseases, especially cancer, wherein mucin expression and glycosylation patterns are altered. Mucin biology has been difficult to study at the molecular level, in part, because methods to manipulate and structurally characterize mucin domains are lacking. Here, we demonstrate that secreted protease of C1 esterase inhibitor (StcE), a bacterial protease from Escherichia coli, cleaves mucin domains by recognizing a discrete peptide- and glycan-based motif. We exploited StcE's unique properties to improve sequence coverage, glycosite mapping, and glycoform analysis of recombinant human mucins by mass spectrometry. We also found that StcE digests cancer-associated mucins from cultured cells and from ascites fluid derived from patients with ovarian cancer. Finally, using StcE, we discovered that sialic acid-binding Ig-type lectin-7 (Siglec-7), a glycoimmune checkpoint receptor, selectively binds sialomucins as biological ligands, whereas the related receptor Siglec-9 does not. Mucin-selective proteolysis, as exemplified by StcE, is therefore a powerful tool for the study of mucin domain structure and function.

The StcE metalloprotease of enterohaemorrhagic Escherichia coli reduces the inner mucus layer and promotes adherence to human colonic epithelium ex vivo

Enterohaemorrhagic Escherichia coli (EHEC) is a major foodborne pathogen and tightly adheres to human colonic epithelium by forming attaching/effacing lesions. To reach the epithelial surface, EHEC must penetrate the thick mucus layer protecting the colonic epithelium. In this study, we investigated how EHEC interacts with the intestinal mucus layer using mucin‐producing LS174T colon carcinoma cells and human colonic mucosal biopsies. The level of EHEC binding and attaching/effacing lesion formation in LS174T cells was higher compared to mucin‐deficient colon carcinoma cell lines, and initial adherence was independent of the presence of flagellin, Escherichia coli common pilus, or long polar fimbriae. Although EHEC infection did not affect gene expression of secreted mucins, it resulted in reduced MUC2 glycoprotein levels. This effect was dependent on the catalytic activity of the secreted metalloprotease StcE, which reduced the inner mucus layer and thereby promoted EHEC access and binding to the epithelium in vitro and ex vivo. Given the lack of efficient therapies against EHEC infection, StcE may represent a suitable target for future treatment and prevention strategies.

Enteric Pathogens Exploit the Microbiota-generated Nutritional Environment of the Gut

Host bacterial associations have a profound impact on health and disease. The human gastrointestinal (GI) tract is inhabited by trillions of commensal bacteria that aid in the digestion of food and vitamin production and play crucial roles in human physiology. Disruption of these relationships and the structure of the bacterial communities that inhabit the gut can contribute to dysbiosis, leading to disease. This fundamental relationship between the host and microbiota relies on chemical signaling and nutrient availability and exchange. GI pathogens compete with the endogenous microbiota for a colonization niche (1, 2). The ability to monitor nutrients and combine this information with the host physiological state is important for the pathogen to precisely program the expression of its virulence repertoire. A major nutrient source is carbon, and although the impact of carbon nutrition on the colonization of the gut by the microbiota has been extensively studied, the extent to which carbon sources affect the regulation of virulence factors by invading pathogens has not been fully defined. The GI pathogen enterohemorrhagic E. coli (EHEC) gages sugar sources as an important cue to regulate expression of its virulence genes. EHEC senses whether it is in a gluconeogenic versus a glycolytic environment, as well as fluctuations of fucose levels to fine tune regulation of its virulence repertoire.

Enterohemorrhagic Escherichia coli reduce mucus and intermicrovillar bridges in human stem cell-derived colonoids

BACKGROUND AND AIMS

Enterohemorrhagic E. coli (EHEC) causes over 70,000 episodes of foodborne diarrhea annually in the USA. The early sequence of events which precede life-threatening hemorrhagic colitis and hemolytic uremic syndrome are not fully understood due to the initial asymptomatic phase of the disease and the lack of a suitable animal model. The aim of this study was to determine the initial molecular events in the interaction between EHEC and human colonic epithelium.

METHODS

Human colonoids derived from adult proximal colonic stem cells were developed into monolayers to study EHEC-epithelial interactions. Monolayer confluency and differentiation were monitored by transepithelial electrical resistance (TER) measurements. The monolayers were apically infected with EHEC and the progression of epithelial damage over time was assessed using biochemical and imaging approaches.

RESULTS

Human colonoid cultures recapitulate the differential protein expression patterns characteristic of the crypt and surface colonocytes. Mucus-producing differentiated colonoid monolayers are preferentially colonized by EHEC. Upon colonization, EHEC forms characteristic attaching and effacing lesions on the apical surface of colonoid monolayers. Mucin 2, a main component of colonic mucus, and protocadherin 24 (PCDH24), a microvillar resident protein, are targeted by EHEC at early stages of infection. The EHEC secreted serine protease, EspP, initiates brush border damage through PCDH24 reduction.

CONCLUSIONS

Human colonoid monolayers are a relevant pathophysiological model which allows the study of early molecular events during enteric infections. Colonoid monolayers provide access to both apical and basolateral surfaces, thus providing an advantage over 3D cultures to study host-pathogen interactions in a controllable and tractable manner. EHEC reduces colonic mucus and affects the brush border cytoskeleton in the absence of commensal bacteria.

Selective cleavage of human sex hormone-binding globulin by kallikrein-related peptidases and effects on androgen action in LNCaP prostate cancer cells

Stimulation of the androgen receptor via bioavailable androgens, including testosterone and testosterone metabolites, is a key driver of prostate development and the early stages of prostate cancer. Androgens are hydrophobic and as such require carrier proteins, including sex hormone-binding globulin (SHBG), to enable efficient distribution from sites of biosynthesis to target tissues. The similarly hydrophobic corticosteroids also require a carrier protein whose affinity for steroid is modulated by proteolysis. However, proteolytic mechanisms regulating the SHBG/androgen complex have not been reported. Here, we show that the cancer-associated serine proteases, kallikrein-related peptidase (KLK)4 and KLK14, bind strongly to SHBG in glutathione S-transferase interaction analyses. Further, we demonstrate that active KLK4 and KLK14 cleave human SHBG at unique sites and in an androgen-dependent manner. KLK4 separated androgen-free SHBG into its two laminin G-like (LG) domains that were subsequently proteolytically stable even after prolonged digestion, whereas a catalytically equivalent amount of KLK14 reduced SHBG to small peptide fragments over the same period. Conversely, proteolysis of 5α-dihydrotestosterone (DHT)-bound SHBG was similar for both KLKs and left the steroid binding LG4 domain intact. Characterization of this proteolysis fragment by [(3)H]-labeled DHT binding assays revealed that it retained identical affinity for androgen compared with full-length SHBG (dissociation constant = 1.92 nM). Consistent with this, both full-length SHBG and SHBG-LG4 significantly increased DHT-mediated transcriptional activity of the androgen receptor compared with DHT delivered without carrier protein. Collectively, these data provide the first evidence that SHBG is a target for proteolysis and demonstrate that a stable fragment derived from proteolysis of steroid-bound SHBG retains binding function in vitro.

Repression of flagella motility in enterohemorrhagic Escherichia coli O157:H7 by mucin components

Whole genome-scale transcriptome analysis of enterohemorrhagic Escherichia coli (EHEC) O157:H7 EDL933 was performed to investigate the influence of mucin components on the EHEC gene expression. Here we report that the 732 candidate genes were differentially expressed by the presence of 0.5% porcine stomach mucin, including the 8 flagella-related genes. Quantitative real-time PCR analyses revealed that the transcription expression of the flg genes (encoding the structural components for flagella basal body) was down-regulated by the mucin components. Indeed, bacterial swarming motility was drastically reduced when grown on 0.3% trypton agar plates containing the mucin. These results imply that gastrointestinal (GI) mucin is a possible environmental signal which negatively regulates the flagellation of EHEC O157:H7 in the GI tract.

Norwegian sheep are an important reservoir for human-pathogenic Escherichia coli O26:H11

A previous national survey of Escherichia coli in Norwegian sheep detected eae-positive (eae(+)) E. coli O26:H11 isolates in 16.3% (80/491) of the flocks. The purpose of the present study was to evaluate the human-pathogenic potential of these ovine isolates by comparing them with E. coli O26 isolates from humans infected in Norway. All human E. coli O26 isolates studied carried the eae gene and shared flagellar type H11. Two-thirds of the sheep flocks and 95.1% of the patients harbored isolates containing arcA allele type 2 and espK and were classified as enterohemorrhagic E. coli (EHEC) (stx positive) or EHEC-like (stx negative). These isolates were further divided into group A (EspK2 positive), associated with stx(2-EDL933) and stcE(O103), and group B (EspK1 positive), associated with stx(1a). Although the stx genes were more frequently present in isolates from patients (46.3%) than in those from sheep flocks (5%), more than half of the ovine isolates in the EHEC/EHEC-like group had multiple-locus variable number of tandem repeat analysis (MLVA) profiles that were identical to those seen in stx-positive human O26:H11 isolates. This indicates that EHEC-like ovine isolates may be able to acquire stx-carrying bacteriophages and thereby have the possibility to cause serious illness in humans. The remaining one-third of the sheep flocks and two of the patients had isolates fulfilling the criteria for atypical enteropathogenic E. coli (aEPEC): arcA allele type 1 and espK negative (group C). The majority of these ovine isolates showed MLVA profiles not previously seen in E. coli O26:H11 isolates from humans. However, according to their virulence gene profile, the aEPEC ovine isolates should be considered potentially pathogenic for humans. In conclusion, sheep are an important reservoir of human-pathogenic E. coli O26:H11 isolates in Norway.

Treatment of enterohemorrhagic Escherichia coli (EHEC) infection and hemolytic uremic syndrome (HUS)

Verotoxigenic Escherichia coli (VTEC) are a specialized group of E. coli that can cause severe colonic disease and renal failure. Their pathogenicity derives from virulence factors that enable the bacteria to colonize the colon and deliver extremely powerful toxins known as verotoxins (VT) or Shiga toxins (Stx) to the systemic circulation. The recent devastating E. coli O104:H4 epidemic in Europe has shown how helpless medical professionals are in terms of offering effective therapies. By examining the sources and distribution of these bacteria, and how they cause disease, we will be in a better position to prevent and treat the inevitable future cases of sporadic disease and victims of common source outbreaks. Due to the complexity of pathogenesis, it is likely a multitargeted approach is warranted. Developments in terms of these treatments are discussed.

Atypical Shigella boydii 13 encodes virulence factors seen in attaching and effacing Escherichia coli

Enterohemorrhagic Escherichia coli (EHEC) is a foodborne pathogen that causes watery diarrhea and hemorrhagic colitis. In this study, we identified StcE, a secreted zinc metalloprotease that contributes to intimate adherence of EHEC to host cells, in culture supernatants of atypical Shigella boydii 13 (Shigella B13) strains. Further examination of the Shigella B13 strains revealed that this cluster of pathogens does not invade but forms pedestals on HEp-2 cells similar to EHEC and enteropathogenic E. coli. This study also demonstrates that atypical Shigella B13 strains are more closely related to attaching and effacing E. coli and that their evolution recapitulates the progression from ancestral E. coli to EHEC.

Mucin dynamics and enteric pathogens

The extracellular secreted mucus and the cell surface glycocalyx prevent infection by the vast numbers of microorganisms that live in the healthy gut. Mucin glycoproteins are the major component of these barriers. In this Review, we describe the components of the secreted and cell surface mucosal barriers and the evidence that they form an effective barricade against potential pathogens. However, successful enteric pathogens have evolved strategies to circumvent these barriers. We discuss the interactions between enteric pathogens and mucins, and the mechanisms that these pathogens use to disrupt and avoid mucosal barriers. In addition, we describe dynamic alterations in the mucin barrier that are driven by host innate and adaptive immune responses to infection.

Multiplex PCR assay for the detection of five putative virulence genes encoded in verotoxigenic Escherichia coli plasmids

The aim was to perform a pentavalent PCR assay for the detection of putative virulence genes encoded in VTEC plasmids, katP, espP, subA, stcE, and ehxA. The five-specific primer pairs used in the assay do not interfere with each other and generate amplification products of 914, 774, 556, 399, and 262 bp. It was selected at random 39 strains belonged to 20 serotypes in order to evaluate the multiplex in a wide variety of strains. The results of this study indicate that it is possible to perform simultaneous amplification and search for recognized plasmid-encoded virulence markers from different E. coli serotypes and apply this technique to the genetic characterization of E. coli strains isolated from reservoirs, foods or patients. This complementary technique is a useful tool to detect interstrain differences for epidemiological studies and to provide information that could be related to the risk of human infection.

TagA is a secreted protease of Vibrio cholerae that specifically cleaves mucin glycoproteins

Vibrio cholerae is a human diarrhoeal pathogen that is a major cause of gastrointestinal disease and death worldwide. Pathogenic V. cholerae strains are characterized by the presence of a Vibrio pathogenicity island (VPI) that encodes virulence factors, including the toxin co-regulated pilus (TCP). TagA is encoded within the VPI and is positively co-regulated with cholera toxin and TCP. TagA is a sequelogue of the StcE mucinase of Escherichia coli O157 : H7. We investigated whether this sequence homology reflected a conserved enzymic substrate profile. TagA exhibited metalloprotease activity toward crude purified mucins, salivary mucin and LS174T goblet cell surface mucin. Like StcE, TagA did not cleave general protease substrates, but unlike StcE, TagA did not cleave the mucin-like serpin C1 esterase inhibitor. Both proteins cleaved the immune cell surface mucin CD43, but TagA demonstrated reduced enzymic efficiency relative to StcE. TagA was expressed and secreted by V. cholerae under ToxR-dependent conditions. A tagA-deficient V. cholerae strain showed no defect in a model of in vitro attachment to the HEp-2 cell line; however, overexpression of a proteolytically inactive mutant, TagA(E433D), caused a significant increase in attachment. The increased attachment was reduced by pretreatment of epithelial monolayers with active TagA. Our results indicate that TagA is a mucinase and suggest that TagA may directly modify host cell surface molecules during V. cholerae infection.

EspP, a serine protease of enterohemorrhagic Escherichia coli, impairs complement activation by cleaving complement factors C3/C3b and C5

Hemolytic-uremic syndrome (HUS) is a life-threatening disorder characterized by hemolytic anemia, thrombocytopenia, and renal insufficiency. It is caused mainly by infections with enterohemorrhagic Escherichia coli (EHEC). Recently, Shiga toxin 2, the best-studied virulence factor of EHEC, was reported to interact with complement, implying that complement may be involved in the pathogenesis of EHEC-induced HUS. The aim of the present study was to investigate whether or not the serine protease EspP, an important virulence factor of EHEC, interacts with complement proteins. EspP did not have any effect on the integrity of factor H or factor I. However, EspP was shown to cleave purified C3/C3b and C5. Cleavage of the respective complement proteins also occurred in normal human serum (NHS) as a source of C3/C3b or C5 or when purified complement proteins were added to the supernatant of an EspP-producing wild-type strain. Edman degradation allowed unequivocal mapping of all three main C3b fragments but not of the three main C5 fragments. Complement activation was significantly downregulated in all three pathways for C5-depleted serum to which C5, preincubated with EspP, was added (whereas C5 preincubated with an EspP mutant was able to fully reconstitute complement activation). This indicates that EspP markedly destroyed the functional activity, as measured by a commercial total complement enzyme-linked immunosorbent assay (Wieslab). Downregulation of complement by EspP in vivo may influence the colonization of EHEC bacteria in the gut or the disease severity of HUS.

Muc2 protects against lethal infectious colitis by disassociating pathogenic and commensal bacteria from the colonic mucosa

Despite recent advances in our understanding of the pathogenesis of attaching and effacing (A/E) Escherichia coli infections, the mechanisms by which the host defends against these microbes are unclear. The goal of this study was to determine the role of goblet cell-derived Muc2, the major intestinal secretory mucin and primary component of the mucus layer, in host protection against A/E pathogens. To assess the role of Muc2 during A/E bacterial infections, we inoculated Muc2 deficient (Muc2^−/−) mice with Citrobacter rodentium, a murine A/E pathogen related to diarrheagenic A/E E. coli. Unlike wildtype (WT) mice, infected Muc2^−/− mice exhibited rapid weight loss and suffered up to 90% mortality. Stool plating demonstrated 10–100 fold greater C. rodentium burdens in Muc2^−/− vs. WT mice, most of which were found to be loosely adherent to the colonic mucosa. Histology of Muc2^−/− mice revealed ulceration in the colon amid focal bacterial microcolonies. Metabolic labeling of secreted mucins in the large intestine demonstrated that mucin secretion was markedly increased in WT mice during infection compared to uninfected controls, suggesting that the host uses increased mucin release to flush pathogens from the mucosal surface. Muc2 also impacted host-commensal interactions during infection, as FISH analysis revealed C. rodentium microcolonies contained numerous commensal microbes, which was not observed in WT mice. Orally administered FITC-Dextran and FISH staining showed significantly worsened intestinal barrier disruption in Muc2^−/− vs. WT mice, with overt pathogen and commensal translocation into the Muc2^−/− colonic mucosa. Interestingly, commensal depletion enhanced C. rodentium colonization of Muc2^−/− mice, although colonic pathology was not significantly altered. In conclusion, Muc2 production is critical for host protection during A/E bacterial infections, by limiting overall pathogen and commensal numbers associated with the colonic mucosal surface. Such actions limit tissue damage and translocation of pathogenic and commensal bacteria across the epithelium.

Enteropathogenic E. coli (EPEC) and Enterohemorrhagic E. coli (EHEC) are important causes of diarrheal disease and other serious complications worldwide. Despite many studies addressing the pathogenic strategies used by these microbes, how the host protects itself from these pathogens is poorly understood. A critical question we address here is whether the thick mucus layer that overlies the intestinal surface plays a role in host protection. Since EPEC and EHEC do not infect mice efficiently, we used a related mouse pathogen called Citrobacter rodentium to infect and compare responses between wildtype mice and Muc2-deficient mice, which are defective in mucus production. We show that Muc2-deficient mice are extremely susceptible to C. rodentium infection-induced mortality and disease. Muc2-deficient mice were also colonized faster and had higher pathogen burdens throughout the experiment. Resident (non-pathogenic) bacteria were found to interact with C. rodentium and host tissues in Muc2-deficient mice, indicating Muc2 regulates all forms of intestinal microbiota at the gut surface. Deficiency in mucus production also contributed to increased leakiness of the gut, which allowed microbes to enter mucosal tissues. Our study shows that Muc2-dependent mucus production is critical for effective management of both pathogenic and non-pathogenic bacteria during infection by an EPEC/EHEC-like pathogen.

Enterohemorrhagic Escherichia coli suppresses inflammatory response to cytokines and its own toxin

Infection with the enteric pathogen enterohemorrhagic Escherichia coli (EHEC) causes a variety of symptoms ranging from nonbloody diarrhea to more severe sequelae including hemorrhagic colitis, altered sensorium and seizures, and even life-threatening complications, such as hemolytic uremic syndrome and thrombotic thrombocytopenic purpura. The more severe consequences of EHEC infection are attributable to the production of Shiga toxin (Stx) and its subsequent effects on the vasculature, which expresses high levels of the Stx receptor, Gb3. Interestingly, the intestinal epithelium does not express Gb3. Despite the lack of Gb3 receptor expression, intestinal epithelial cells translocate Stx. The effect of Stx on intestinal epithelial cells is controversial with some studies demonstrating induction of inflammation and others not. This may be difficult to resolve because EHEC expresses both proinflammatory molecules, such as flagellin, and factor(s) that dampen the inflammatory response of epithelial cells. The goal of our study was to define the effect of Stx on the inflammatory response of intestinal epithelial cells and to determine whether infection by EHEC modulates this response. Here we show that Stx is a potent inducer of the inflammatory response in intestinal epithelial cells and confirm that EHEC attenuates the induction of IL-8 by host-derived proinflammatory cytokines. More importantly, however, we show that infection with EHEC attenuates the inflammatory response by intestinal epithelial cells to its own toxin. We speculate that the ability of EHEC to dampen epithelial cell inflammatory responses to Stx and cytokines facilitates intestinal colonization.

Enterohemorrhagic Escherichia coli O157:H7 gene expression profiling in response to growth in the presence of host epithelia

Background

The pathogenesis of enterohemorrhagic Escherichia coli (EHEC) O157∶H7 infection is attributed to virulence factors encoded on multiple pathogenicity islands. Previous studies have shown that EHEC O157∶H7 modulates host cell signal transduction cascades, independent of toxins and rearrangement of the cytoskeleton. However, the virulence factors and mechanisms responsible for EHEC-mediated subversion of signal transduction remain to be determined. Therefore, the purpose of this study was to first identify differentially regulated genes in response to EHEC O157∶H7 grown in the presence of epithelial cells, compared to growth in the absence of epithelial cells (that is, growth in minimal essential tissue culture medium alone, minimal essential tissue culture medium in the presence of 5% CO₂, and Penassay broth alone) and, second, to identify EHEC virulence factors responsible for pathogen modulation of host cell signal transduction.

Methodology/Principal Findings

Overnight cultures of EHEC O157∶H7 were incubated for 6 hr at 37°C in the presence or absence of confluent epithelial (HEp-2) cells. Total RNA was then extracted and used for microarray analyses (Affymetrix E. coli Genome 2.0 gene chips). Relative to bacteria grown in each of the other conditions, EHEC O157∶H7 cultured in the presence of cultured epithelial cells displayed a distinct gene-expression profile. A 2.0-fold increase in the expression of 71 genes and a 2.0-fold decrease in expression of 60 other genes were identified in EHEC O157∶H7 grown in the presence of epithelial cells, compared to bacteria grown in media alone.

Conclusion/Significance

Microarray analyses and gene deletion identified a protease on O-island 50, gene Z1787, as a potential virulence factor responsible for mediating EHEC inhibition of the interferon (IFN)-γ-Jak1,2-STAT-1 signal transduction cascade. Up-regulated genes provide novel targets for use in developing strategies to interrupt the infectious process.

Modulation of neutrophil function by a secreted mucinase of Escherichia coli O157:H7

Escherichia coli O157∶H7 is a human enteric pathogen that causes hemorrhagic colitis which can progress to hemolytic uremic syndrome, a severe kidney disease with immune involvement. During infection, E. coli O157∶H7 secretes StcE, a metalloprotease that promotes the formation of attaching and effacing lesions and inhibits the complement cascade via cleavage of mucin-type glycoproteins. We found that StcE cleaved the mucin-like, immune cell-restricted glycoproteins CD43 and CD45 on the neutrophil surface and altered neutrophil function. Treatment of human neutrophils with StcE led to increased respiratory burst production and increased cell adhesion. StcE-treated neutrophils exhibited an elongated morphology with defective rear detachment and impaired migration, suggesting that removal of the anti-adhesive capability of CD43 by StcE impairs rear release. Use of zebrafish embryos to model neutrophil migration revealed that StcE induced neutrophil retention in the fin after tissue wounding, suggesting that StcE modulates neutrophil-mediated inflammation in vivo. Neutrophils are crucial innate effectors of the antibacterial immune response and can contribute to severe complications caused by infection with E. coli O157∶H7. Our data suggest that the StcE mucinase can play an immunomodulatory role by directly altering neutrophil function during infection. StcE may contribute to inflammation and tissue destruction by mediating inappropriate neutrophil adhesion and activation.

Enterohemorrhagic Escherichia coli (EHEC) poses a significant threat to the U.S. food supply, causing foodborne gastrointestinal disease in humans that can progress to hemolytic uremic syndrome (HUS), a potentially fatal kidney disease. Research suggests that EHEC strains are growing more virulent, resulting in a higher incidence of hospitalization and development of HUS from recent produce-associated outbreaks. Although immune dysregulation is a feature of HUS disease, the specific mechanisms contributing to altered immune function require investigation. Furthermore, the contribution of the immune response to early intestinal disease is not known. StcE is a secreted protease of EHEC that is expressed during infection and may contribute to virulence via cleavage of mucin-like glycoproteins. In this study, we define mucinase activity toward glycoproteins on the surface of human neutrophils and find that StcE alters neutrophil activity by interacting with these proteins. StcE affected crucial neutrophil functions including oxidative burst production and migration. The effects of StcE were both cleavage-dependent and cleavage-independent, providing insight into a novel mechanism for mediating neutrophil function via mucin interactions. Our study reports an immune-modulating role for a potential EHEC virulence factor and provides a possible explanation for altered neutrophil phenotypes observed during E. coli O157∶H7-induced disease.

Mucin dynamics in intestinal bacterial infection

BACKGROUND

Bacterial gastroenteritis causes morbidity and mortality in humans worldwide. Murine Citrobacter rodentium infection is a model for gastroenteritis caused by the human pathogens enteropathogenic Escherichia coli and enterohaemorrhagic E. coli. Mucin glycoproteins are the main component of the first barrier that bacteria encounter in the intestinal tract.

METHODOLOGY/PRINCIPAL FINDINGS

Using Immunohistochemistry, we investigated intestinal expression of mucins (Alcian blue/PAS, Muc1, Muc2, Muc4, Muc5AC, Muc13 and Muc3/17) in healthy and C. rodentium infected mice. The majority of the C. rodentium infected mice developed systemic infection and colitis in the mid and distal colon by day 12. C. rodentium bound to the major secreted mucin, Muc2, in vitro, and high numbers of bacteria were found in secreted MUC2 in infected animals in vivo, indicating that mucins may limit bacterial access to the epithelial surface. In the small intestine, caecum and proximal colon, the mucin expression was similar in infected and non-infected animals. In the distal colonic epithelium, all secreted and cell surface mucins decreased with the exception of the Muc1 cell surface mucin which increased after infection (p<0.05). Similarly, during human infection Salmonella St Paul, Campylobacter jejuni and Clostridium difficile induced MUC1 in the colon.

CONCLUSION

Major changes in both the cell-surface and secreted mucins occur in response to intestinal infection.