The Type Three Secretion System 2-Encoded Regulator EtrB Modulates Enterohemorrhagic Escherichia coli Virulence Gene Expression

Genomic island-encoded regulatory proteins in enterohemorrhagic Escherichia coli O157:H7

Enterohemorrhagic Escherichia coli (EHEC) is an important zoonotic pathogen that is a major cause of foodborne diseases in most developed and developing countries and can cause uncomplicated diarrhoea, haemorrhagic colitis, and haemolytic uraemic syndrome. O islands (OIs), which are unique genomic islands in EHEC O157:H7, are composed of 177 isolated genomic features and harbour 26% of the total genes that are absent in the non-pathogenic E. coli K-12 genome. In the last twenty years, many OI-encoded proteins have been characterized, including proteins regulating virulence, motility, and acid resistance. Given the critical role of regulatory proteins in the systematic and hierarchical regulation of bacterial biological processes, this review summarizes the OI-encoded regulatory proteins in EHEC O157:H7 characterized to date, emphasizing OI-encoded regulatory proteins for bacterial virulence, motility, and acid resistance. This summary will be significant for further exploration and understanding of the virulence and pathogenesis of EHEC O157:H7.

The yad and yeh fimbrial loci influence gene expression and virulence in enterohemorrhagic Escherichia coli O157:H7

Fimbriae are essential virulence factors for many bacterial pathogens. Fimbriae are extracellular structures that attach bacteria to surfaces. Thus, fimbriae mediate a critical step required for any pathogen to establish infection by anchoring a bacterium to host tissue. The human pathogen enterohemorrhagic Escherichia coli (EHEC) O157:H7encodes 16 fimbriae that may be important for EHEC to initiate infection and allow for productive expression of virulence traits important in later stages of infection, including a type III secretion system (T3SS) and Shiga toxin; however, the roles of most EHEC fimbriae are largely uncharacterized. Here, we provide evidence that two EHEC fimbriae, Yad and Yeh, modulate expression of diverse genes including genes encoding T3SS and Shiga toxin and that these fimbriae are required for robust colonization of the gastrointestinal tract. These findings reveal a significant and previously unappreciated role for fimbriae in bacterial pathogenesis as important determinants of virulence gene expression.IMPORTANCEFimbriae are extracellular proteinaceous structures whose defining role is to anchor bacteria to surfaces. This is a fundamental step for bacterial pathogens to establish infection in a host. Here, we show that the contributions of fimbriae to pathogenesis are more complex. Specifically, we demonstrate that fimbriae influence expression of virulence traits essential for disease progression in the intestinal pathogen enterohemorrhagic Escherichia coli. Gram-positive and Gram-negative bacteria express multiple fimbriae; therefore, these findings may have broad implications for understanding how pathogens use fimbriae, beyond adhesion, to initiate infection and coordinate gene expression, which ultimately results in disease.

Genetic distribution, characterization, and function of Escherichia coli type III secretion system 2 (ETT2)

Many Gram-negative bacteria use type Ⅲ secretion system (T3SS) to inject effector proteins and subvert host signaling pathways, facilitating the growth, survival, and virulence. Notably, some bacteria harbor multiple distinct T3SSs with different functions. An extraordinary T3SS, the Escherichia coli Type III Secretion System 2 (ETT2), is widespread among Escherichia coli (E. coli) strains. Since many ETT2 carry genetic mutations or deletions, it is thought to be nonfunctional. However, increasing studies highlight ETT2 contributes to E. coli pathogenesis. Here, we present a comprehensive overview of genetic distribution and characterization of ETT2. Subsequently, we outline its functional potential, contending that an intact ETT2 may retain the capacity to translocate effector proteins and manipulate the host's innate immune response. Given the potential zoonotic implications associated with ETT2-carrying bacteria, further investigations into the structure, function and regulation of ETT2 are imperative for comprehensive understanding of E. coli pathogenicity and the development of effective control strategies.

Regulation Mechanisms of Virulence Genes in Enterohemorrhagic Escherichia coli

Enterohemorrhagic Escherichia coli (EHEC) is one of the most common E. coli pathotypes reported to cause several outbreaks of foodborne illnesses. EHEC is a zoonotic pathogen, and ruminants, especially cattle, are considered important reservoirs for the most common EHEC serotype, E. coli O157:H7. Humans are infected indirectly through the consumption of food (milk, meat, leafy vegetables, and fruits) and water contaminated by animal feces or direct contact with carrier animals or humans. E. coli O157:H7 is one of the most frequently reported causes of foodborne illnesses in developed countries. It employs two essential virulence mechanisms to trigger damage to the host. These are the development of attaching and effacing (AE) phenotypes on the intestinal mucosa of the host and the production of Shiga toxin (Stx) that causes hemorrhagic colitis and hemolytic uremic syndrome. The AE phenotype is controlled by the pathogenicity island, the locus of enterocyte effacement (LEE). The induction of both AE and Stx is under strict and highly complex regulatory mechanisms. Thus, a good understanding of these mechanisms, major proteins expressed, and environmental cues involved in the regulation of the expression of the virulence genes is vital to finding a method to control the colonization of reservoir hosts, especially cattle, and disease development in humans. This review is a concise account of the current state of knowledge of virulence gene regulation in the LEE-positive EHEC.

Molecular Study to Detect Escherichia coli in Diarrheic Children and its Antibiotic Resistance

Diarrheal diseases can lead to infections and cause morbidity and mortality in children. Diarrheagenic Escherichia coli (DEC) is an etiological agent, which is considered the major causative agent of diarrhea in children in some developing countries. The aims of this work were to estimate Escherichia coli (E. coli) causing diarrhea in children less than 5 years old, and to detect some biofilm virulence factors and the effect of some antibiotics. For the methodology, a total of 112 specimens were collected from children from two health centers, Al-Zahraa Teaching Hospital and Public Health Laboratory (located in Al-Kut city/ and the Wasit province in Iraq). All specimens were grown on simple and rich media. A total of 43 (38.4%) E. coli isolates were identified using different traditional methods, such as biochemical tests and 16S rRNA sequencing. Polymerase chain reaction (PCR) testing was used to detect some virulence factor genes that play an important role in the pathogenesis of diarrheic E. coli e.g., 16S rRNA, bfpA, and eaeA. In this study, several antibiotics were used to estimate the sensitivity and resistivity of E. coli isolates. A total of 43 isolates were fully identified as E. coli. These samples were used to detect the virulence factor genes, and 31 (72.1%) and 29 (29.4%) isolates carried bfpA and eaeA, respectively. The preponderance of E. coli isolates were completely resistant to penicillin 43 (100%). Additionally, 33 (76.7%) and 27 (62.8%) isolates were resistant to cephalothin and amoxycillin-clavulanic acid, respectively. Furthermore, the isolates of E. coli isolates showed different levels of sensitivity to antibiotics, including polymyxin B 40 (93%), norfloxacin 38 (88.4%), gentamycin 26 (60.4%), and meropenem 22 (51.2%). In conclusion, diarrheagenic E. coli isolates were the prevalent among diarrheic children. Most isolates showed varying results for the presence of virulence factors. In addition, all isolates were resistant to penicillin and sensitive to polymyxin B.

YqeH contributes to avian pathogenic Escherichia coli pathogenicity by regulating motility, biofilm formation, and virulence

Avian pathogenic Escherichia coli (APEC) is a pathotype of extraintestinal pathogenic E. coli and one of the most serious infectious diseases of poultry. It not only causes great economic losses to the poultry industry, but also poses a serious threat to public health worldwide. Here, we examined the role of YqeH, a transcriptional regulator located at E. coli type III secretion system 2 (ETT2), in APEC pathogenesis. To investigate the effects of YqeH on APEC phenotype and virulence, we constructed a yqeH deletion mutant (APEC40-ΔyqeH) and a complemented strain (APEC40-CΔyqeH) of APEC40. Compared with the wild type (WT), the motility and biofilm formation of APEC40-ΔyqeH were significantly reduced. The yqeH mutant was highly attenuated in a chick infection model compared with WT, and showed severe defects in its adherence to and invasion of chicken embryo fibroblast DF-1 cells. However, the mechanisms underlying these phenomena were unclear. Therefore, we analyzed the transcriptional effects of the yqeH deletion to clarify the regulatory mechanisms of YqeH, and the role of YqeH in APEC virulence. The deletion of yqeH downregulated the transcript levels of several flagellum-, biofilm-, and virulence-related genes. Our results demonstrate that YqeH is involved in APEC pathogenesis, and the reduced virulence of APEC40-ΔyqeH may be related to its reduced motility and biofilm formation.

Virulence-related O islands in enterohemorrhagic Escherichia coli O157:H7

Enterohemorrhagic Escherichia coli (EHEC) O157:H7 is a principally foodborne pathogen linked to serious diseases, including bloody diarrhea, hemorrhagic colitis, and hemolytic uremic syndrome. Comparative genomics analysis revealed that EHEC O157 contains 177 unique genomic islands, termed O islands, compared with the nonpathogenic E. coli K-12 laboratory strain. These O islands contribute largely to the pathogenicity of EHEC O157:H7 by providing numerous virulence factors, effectors, virulence regulatory proteins, and virulence regulatory sRNAs. The present review aimed to provide a comprehensive understanding of the research progress on the function of O islands, especially focusing on virulence-related O islands.

The Escherichia coli type III secretion system 2 Is involved in the biofilm formation and virulence of avian Pathogenic Escherichia coli

The Escherichia coli type III secretion system 2 (ETT2) is found in most pathogenic E. coli strains. Although many ETT2 gene clusters carry multiple genetic mutations or deletions, ETT2 is known to be involved in bacterial virulence. To date, no studies have been conducted on the role of ETT2 in the virulence of avian pathogenic Escherichia coli (APEC), which harbours ETT2. Thus, we deleted the ETT2 of APEC strain and evaluated the phenotypes and pathogenicities of the mutant. The results showed that deletion of ETT2 had no effect on APEC growth, but significantly promoted biofilm formation. In addition, as compared to the wild-type （WT） strain, the ETT2 deletion significantly promoted adherence to and invasion of DF-1 chicken fibroblasts and facilitated survival in the sera of specific-pathogen-free chickens. Analysis of the role of ETT2 in animal infection models demonstrated that the distribution of viable bacteria in the blood and organs of chicks infected with the ΔETT2 was significantly higher than those infected with WT. The results of RNA sequencing indicated that multiple genes involved in biofilm formation, lipopolysaccharide components, fimbrial genes and virulence effector proteins are regulated by ETT2. Collectively, these results implicated ETT2 is involved in the biofilm formation and pathogenicity of APEC.

The ETT2 transcriptional regulator EivF affects the serum resistance and pathogenicity of avian pathogenic Escherichia coli

Avian pathogenic Escherichia coli (APEC), a pathotype of extraintestinal pathogenic Escherichia coli (ExPEC), can cause serious systemic infectious diseases in poultry. Escherichia coli type III secretion system 2 (ETT2) is widely distributed in E. coli strains, including ExPEC and Enterohemorrhagic Escherichia coli (EHEC). The transcriptional regulator EivF, which is located at the ETT2 cluster, affects the secretion of LEE-encoded proteins and increases bacterial adhesion to human intestinal epithelial cells in EHEC O157:H7. In a previous study, we demonstrated the transcriptional regulator can affect APEC's motility and biofilm formation. Here, we evaluated whether EivF is involved in the pathogenicity of APEC, and we found that inactivation of eivF significantly enhanced resistance to the serum, adherence to chicken embryo fibroblast (DF-1) cells, and the colonization ability of APEC in chicks. To further clarify the regulation mechanism of transcriptional regulator EivF, we performed transcriptome sequencing to analyze the differentially expressed genes and pathways, showing that EivF regulates membrane, adhesion, environmental stress, and secretion protein genes, and EivF is involved in the localization, biological adhesion, biological regulation, membrane, and toxin activity. These findings indicated that the ETT2 transcriptional regulator EivF plays a crucial role in the pathogenicity of APEC as a negative repressor.

Transcription Regulator YgeK Affects the Virulence of Avian Pathogenic Escherichia coli

Simple Summary

Avian pathogenic Escherichia coli (APEC) is the responsible pathogen for colibacillosis in poultry. Transcriptional regulator YgeK was a transcriptional regulator locating at E. coli type three secretion system 2 (ETT2) in APEC. However, the role of YgeK in APEC has not been reported. In this study, we found that the inactivation of YgeK in APEC decreased the flagellar formation ability, bacterial motility ability, serum sensitivity, adhesion ability, and virulence. Results suggested that the transcriptional regulator YgeK plays a crucial role in APEC virulence.

Abstract

Avian pathogenic Escherichia coli (APEC) is the responsible pathogen for colibacillosis in poultry, and is a potential gene source for human extraintestinal pathogenic Escherichia coli. Escherichia coli type III secretion system 2 (ETT2) is widely distributed in human and animal ExPEC isolates, and is crucial for the virulence of ExPEC. Transcriptional regulator YgeK, located in the ETT2 gene cluster, was identified as an important regulator of gene expression in enterohemorrhagic E. coli (EHEC). However, the role of YgeK in APEC has not been reported. In this study, we performed amino acid alignment analysis of YgeK among different E. coli strains and generated ygeK mutant strain AE81ΔygeK from clinical APEC strain AE81. Flagellar formation, bacterial motility, serum sensitivity, adhesion, and virulence were all significantly reduced following the inactivation of YgeK in APEC. Then, we performed transcriptome sequencing to analyze the functional pathways involved in the biological processes. Results suggested that ETT2 transcriptional regulator YgeK plays a crucial role in APEC virulence. These findings thus contribute to our understanding of the function of the ETT2 cluster, and clarify the pathogenic mechanism of APEC.

Escherichia coli ST302: Genomic Analysis of Virulence Potential and Antimicrobial Resistance Mediated by Mobile Genetic Elements

aEPEC are associated with persistent diarrhea, and diarrheal outbreaks in both humans and animals worldwide. They are differentiated from typical EPEC by the lack of bundle-forming pili, and from EHEC by the lack of phage-mediated stx toxins. However, phylogenetic analyses often associate aEPEC with EHEC, promoting the hypothesis that aEPEC are the progenitors of EHEC, which is supported by aEPEC conversion to EHEC by stx-carrying phages. While aEPEC can cause disease outright, the potential to acquire stx, one of the most potent bacterial toxins known, merits close monitoring. Escherichia coli ST302 (O108:H9, O182:H9, O45:H9) are aEPEC that have been isolated from diarrheic human, pig and rabbit hosts, as well as in healthy pigs, however, no study to date has focused on E. coli ST302 strains. Through WGS and hybrid assembly we present the first closed chromosome, and two circularized plasmids of an ST302 strain - F2_18C, isolated from a healthy pig in Australia. A phylogenetic analysis placed E. coli ST302 strains in proximity to EHEC ST32 (O145:H28) strains. Public databases were interrogated for WGSs of E. coli ST302 strains and short-read gene screens were used to compare their virulence-associated gene (VAG) and antimicrobial resistance gene (ARG) cargo. E. coli ST302 strains carry diverse VAGs, including those that typically associated with extraintestinal pathogenic E. coli (ExPEC). Plasmid comparisons showed that pF2_18C_FIB shared homology with EHEC virulence plasmids such as pO103 while pF2_18C_HI2 is a large multidrug resistance IncHI2:ST3 plasmid. A comparison of 33 HI2:ST3 plasmids demonstrated that those of Australian origin have not acquired resistances to extended-spectrum beta-lactams, colistin, fosfomycin or rifampicin, unlike those originating from Asia. F2_18C was shown to carry two additional pathogenicity islands – ETT2, and the STEC-associated PAI_CL3, plasmid-associated heavy metal resistance genes, as well as several unoccupied stx-phage attachment sites. This study sheds light on the virulence and AMR potential of E. coli ST302 strains and informs AMR genomic surveillance.

RstA, a two-component response regulator, plays important roles in multiple virulence-associated processes in enterohemorrhagic Escherichia coli O157:H7

Background

Enterohemorrhagic Escherichia coli O157:H7 (EHEC O157) causes bloody diarrhea and hemolytic-uremic syndrome. EHEC O157 encounters varied microenvironments during infection, and can efficiently adapt to these using the two-component system (TCS). Recently, a functional TCS, RstAB, has been implicated in the regulation of virulence of several bacterial pathogens. However, the regulatory function of RstAB in EHEC O157 is poorly understood. This study aimed at providing insights into the global effects of RstA on gene expression in EHEC O157.

Results

In the present study, we analyzed gene expression differences between the EHEC O157 wild-type strain and a ΔrstA mutant using RNA-seq technology. Genes with differential expression in the ΔrstA mutant compared to that in the wild-type strain were identified and grouped into clusters of orthologous categories. RstA promoted EHEC O157 LEE gene expression, adhesion in vitro, and colonization in vivo by indirect regulation. We also found that RstA could bind directly to the promoter region of hdeA and yeaI to enhance acid tolerance and decrease biofilm formation by modulating the concentration of c-di-GMP.

Conclusions

In summary, the RstAB TCS in EHEC O157 plays a major role in the regulation of virulence, acid tolerance, and biofilm formation. We clarified the regulatory function of RstA, providing an insight into mechanisms that may be potential drug targets for treatment of EHEC O157-related infections.

The Type III Secretion System of Pathogenic Escherichia coli

Infection with enteropathogenic and enterohaemorrhagic Escherichia coli (EPEC and EHEC), enteroinvasive E. coli (EIEC) and Shigella relies on the elaboration of a type III secretion system (T3SS). Few strains also encode a second T3SS, named ETT2. Through the integration of coordinated intracellular and extracellular cues, the modular T3SS is assembled within the bacterial cell wall, as well as the plasma membrane of the host cell. As such, the T3SS serves as a conduit, allowing the chaperone-regulated translocation of effector proteins directly into the host cytosol to subvert eukaryotic cell processes. Recent technological advances revealed high structural resolution of the T3SS apparatus and how it could be exploited to treat enteric disease. This chapter summarises the current knowledge of the structure and function of the E. coli T3SSs.

Control freaks-signals and cues governing the regulation of virulence in attaching and effacing pathogens

Enterohaemorrhagic Escherichia coli (EHEC) mediates disease using a type 3 secretion system (T3SS), which is encoded on the locus of enterocyte effacement (LEE) and is tightly controlled by master regulators. This system is further modulated by a number of signals that help to fine-tune virulence, including metabolic, environmental and chemical signals. Since the LEE and its master regulator, Ler, were established, there have been numerous scientific advancements in understanding the regulation and expression of virulence factors in EHEC. This review will discuss the recent advancements in this field since our previous review, with a focus on the transcriptional regulation of the LEE.

Escherichia coli type III secretion system 2 regulator EtrA promotes virulence of avian pathogenic Escherichia coli

The Escherichia coli type III secretion system 2 (ETT2) is found in most E. coli strains, including pathogenic and commensal strains. Although many ETT2 gene clusters carry multiple genetic mutations or deletions, ETT2 is known to be involved in bacterial virulence. In enterohaemorrhagic E. coli (EHEC), ETT2 affects adhesion through the regulator EtrA, which regulates transcription and secretion of the type III secretion system (T3SS) encoded by the locus of enterocyte effacement (LEE). To date, no studies have been conducted on the role of EtrA in the virulence of avian pathogenic E. coli (APEC), which harbours only ETT2. Thus, we constructed etrA mutant and complemented strains of APEC and evaluated their phenotypes and pathogenicities. We found that the etrA gene deletion significantly reduced bacterial survival in macrophages, and proliferation and virulence in ducks. In addition, the etrA gene deletion reduced expression of the APEC fimbriae genes. Upregulation of genes encoding the pro-inflammatory cytokines interleukin (IL)-1β and IL-8 was also observed in HD-11 macrophages infected with the etrA gene mutant strain compared to the wild-type strain. Furthermore, the altered capacities of the mutant strain were restored by genetic complementation. Our observations demonstrate that the ETT2 regulator EtrA contributes to the virulence of APEC.

Identification of different Escherichia coli pathotypes in north and north-west provinces of Iran

BACKGROUND AND OBJECTIVES

Diarrhea is one of the most prevalent diseases in the world, specially in developing countries. One of the most important causative agents of bacterial diarrhea is diarrheagenic Escherichia coli (DEC) which causes gastroenteritis and this group involving enterotoxigenic E. coli (ETEC), enteropathogenic E. coli (EPEC), enteroaggregative E. coli (EAEC), enterohemoragic E. coli (EHEC), enteroinvasive E. coli (EIEC), diffusely adherence E. coli (DAEC). The aim of this study was to identify different E. coli pathotypes in north and north-west of Iran, among the clinical isolates.

MATERIALS AND METHODS

In this study for identification of E. coli, 170 fecal samples were cultured on MacConkey agar and identified by biochemical tests. Samples with E. coli characteristics were selected (145 samples) and their genomes were purified by phenol-chloroform method. After extraction of genomes, lt and sta genes identified by PCR for ETEC, eae gene for atypical and eae and bfp for typical EPEC, AA region for EAEC, stx₁ and stx₂ and eae genes for EHEC (stx₁ or stx₂ or both for STEC) and invE for EIEC.

RESULTS

Finally 10 samples identified as ETEC (%5.88), 18 (%10.58) EPEC, 6 (%3.52) EHEC and 12 (7.05%) samples were STEC. None of the samples were positive for EAEC and EIEC.

CONCLUSION

The results obtained in this study showed that ETEC, EPEC, EHEC and STEC are prevalent bacterial agents in north and north-west of Iran. Complementary studies to identify these pathotypes in other seasons can help to adopt necessary policies against outbreaks in Iran.