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Enteric pathogens such as enterohemorrhagic Escherichia coli (EHEC) and Citrobacter rodentium, which is largely used as a surrogate EHEC model for murine infections, are exposed to several host neurotransmitters in the gut. An important chemical exchange within the gut involves the neurotransmitters epinephrine and/or norepinephrine, extensively reported to increase virulence gene expression in EHEC, acting through two bacterial adrenergic sensors: QseC and QseE. However, EHEC is unable to establish itself and cause its hallmark lesions, attaching and effacing (AE) lesions, on murine enterocytes. To address the role of these neurotransmitters during enteric infection, we employed C. rodentium Both EHEC and C. rodentium harbor the locus of enterocyte effacement (LEE) that is necessary for AE lesion formation. Here we show that expression of the LEE, as well as that of other virulence genes in C. rodentium, is also activated by epinephrine and/or norepinephrine. Both QseC and QseE are required for LEE gene activation in C. rodentium, and the qseC and qseE mutants are attenuated for murine infection. C. rodentium has a decreased ability to colonize dopamine β-hydroxylase knockout (Dbh(-/-)) mice, which do not produce epinephrine and norepinephrine. Both adrenergic sensors are required for C. rodentium to sense these neurotransmitters and activate the LEE genes during infection. These data indicate that epinephrine and norepinephrine are sensed by bacterial adrenergic receptors during enteric infection to promote activation of their virulence repertoire. This is the first report of the role of these neurotransmitters during mammalian gastrointestinal (GI) infection by a noninvasive pathogen. The epinephrine and norepinephrine neurotransmitters play important roles in gut physiology and motility. Of note, epinephrine and norepinephrine play a central role in stress responses in mammals, and stress has profound effects on GI function. Bacterial enteric pathogens exploit these neurotransmitters as signals to coordinate the regulation of their virulence genes. The bacterial QseC and QseE adrenergic sensors are at the center of this regulatory cascade. C. rodentium is a noninvasive murine pathogen with a colonization mechanism similar to that of EHEC, enabling the investigation of host signals in mice. The presence of these neurotransmitters in the gut is necessary for C. rodentium to fully activate its virulence program, in a QseC/QseE-dependent manner, to successfully colonize its murine host. Our study data provide the first example of epinephrine and norepinephrine signaling within the gut to stimulate infection by a bacterial pathogen in a natural animal infection.

The mammalian gastrointestinal tract provides a complex and competitive environment for the microbiota (1). Successful colonization by pathogens requires scavenging nutrients, sensing chemical signals, competing with the resident bacteria and precisely regulating the expression of virulence genes (2). The gastrointestinal pathogen enterohaemorrhagic Escherichia coli(EHEC) relies on inter-kingdom chemical sensing systems to regulate virulence gene expression (3,4). Here we show that these systems control the expression of a novel two-component signal transduction system, named FusKR, where FusK is the histidine sensor kinase and FusR the response regulator. FusK senses fucose and controls expression of virulence and metabolic genes. This fucose-sensing system is required for robust EHEC colonization of the mammalian intestine. Fucose is highly abundant in the intestine (5). Bacteroides thetaiotaomicron produces multiple fucosidases that cleave fucose from host glycans, resulting in high fucose availability in the gut lumen (6). During growth in mucin, B. thetaiotaomicron contributes to EHEC virulence by cleaving fucose from mucin, thereby activating the FusKR signalling cascade, modulating the virulence gene expression of EHEC. Our findings suggest that EHEC uses fucose, a host-derived signal made available by the microbiota, to modulate EHEC pathogenicity and metabolism., The gastrointestinal tract is inhabited by trillions of commensal bacteria that play crucial roles in human physiology (1). This fundamental relationship between the host and microbiota relies on chemical signalling [...]

Background: Bacterial identification at the strain level is a much-needed, but arduous and challenging task. This study aimed to develop a method for identifying and differentiating individual strains among multiple strains of the same bacterial species. The set used for testing the method consisted of 17 Escherichia coli strains picked from a collection of strains isolated in Germany, Spain, the United Kingdom and Vietnam from humans, cattle, swine, wild boars, and chickens. We targeted unique or rare ORFan genes to address the problem of selective and specific strain identification. These ORFan genes, exclusive to each strain, served as templates for developing strain-specific primers. Results: Most of the experimental strains (14 out of 17) possessed unique ORFan genes that were used to develop strain-specific primers. The remaining three strains were identified by combining a PCR for a rare gene with a selection step for isolating the experimental strains. Multiplex PCR allowed the successful identification of the strains both in vitro in spiked faecal material in addition to in vivo after experimental infections of pigs and recovery of bacteria from faecal material. In addition, primers for qPCR were also developed and quantitative readout from faecal samples after experimental infection was also possible. Conclusions: The method described in this manuscript using strain-specific unique genes to identify single strains in a mixture of strains proved itself efficient and reliable in detecting and following individual strains both in vitro and in vivo, representing a fast and inexpensive alternative to more costly methods. [ABSTRACT FROM AUTHOR]

Shiga toxin 2 (Stx2), one of the principal virulence factors of enterohemorrhagic Escherichia coli, is encoded by 933W, a lambda-like prophage. 933W prophage induction contributes to Stx2 production, and here, we provide evidence that Dam methyltransferase is essential for maintenance of 933W lysogeny. Our findings are consistent with the idea that the 933W prophage has a relatively low threshold for induction, which may promote Stx2 production during infection.

The ability of a kanamycin-marked Stx phage to move into a commensal, ovine Escherichia coli strain in the ruminant gastrointestinal tract was assessed. Transduction was detected in 19 out of 24 sheep tested and that the rate of transduction did not increase with subtherapeutic doses of the quinolone antibiotic enrofloxacin.

Research has been conducted on nontoxigenic Escherichia coli O157:H7 chromosomally lux-marked strain. Results demonstrate that survival characteristics of this strain are indistinguishable from the wild-type strain.

Classical studies have focused on the role that individual regulators play in controlling virulence gene expression. An emerging theme, however, is that bacterial metabolism also plays a key role in this process. Our previous work identified a series of proteins that were implicated in the regulation of virulence. One of these proteins was AdhE, a bi-functional acetaldehyde- CoA dehydrogenase and alcohol dehydrogenase. Deletion of its gene ( adhE) resulted in elevated levels of extracellular acetate and a stark pleiotropic phenotype: strong suppression of the Type Three Secretion System ( T3SS) and overexpression of non-functional flagella. Correspondingly, the adhE mutant bound poorly to host cells and was unable to swim. Furthermore, the mutant was significantly less virulent than its parent when tested in vivo, which supports the hypothesis that attachment and motility are central to the colonization process. The molecular basis by which AdhE affects virulence gene regulation was found to be multifactorial, involving acetate-stimulated transcription of flagella expression and post-transcriptional regulation of the T3SS through Hfq. Our study reveals fascinating insights into the links between bacterial physiology, the expression of virulence genes, and the underlying molecular mechanism mechanisms by which these processes are regulated. [ABSTRACT FROM AUTHOR]

Enteric pathogens such as enterohemorrhagic Escherichia coli (EHEC) and Citrobacter rodentium, which is largely used as a surrogate EHEC model for murine infections, are exposed to several host neurotransmitters in the gut. An important chemical exchange within the gut involves the neurotransmitters epinephrine and/or norepinephrine, extensively reported to increase virulence gene expression in EHEC, acting through two bacterial adrenergic sensors: QseC and QseE. However, EHEC is unable to establish itself and cause its hallmark lesions, attaching and effacing (AE) lesions, on murine enterocytes. To address the role of these neurotransmitters during enteric infection, we employed C. rodentium. Both EHEC and C. rodentium harbor the locus of enterocyte effacement (LEE) that is necessary for AE lesion formation. Here we show that expression of the LEE, as well as that of other virulence genes in C. rodentium, is also activated by epinephrine and/or norepinephrine. Both QseC and QseE are required for LEE gene activation in C. rodentium, and the qseC and qseE mutants are attenuated for murine infection. C. rodentium has a decreased ability to colonize dopamine β-hydroxylase knockout (Dbh−/−) mice, which do not produce epinephrine and norepinephrine. Both adrenergic sensors are required for C. rodentium to sense these neurotransmitters and activate the LEE genes during infection. These data indicate that epinephrine and norepinephrine are sensed by bacterial adrenergic receptors during enteric infection to promote activation of their virulence repertoire. This is the first report of the role of these neurotransmitters during mammalian gastrointestinal (GI) infection by a noninvasive pathogen.

Enterohaemorrhagic Escherichia coli (EHEC) O157:H7 induces filamentous actin-rich ‘pedestals’ on intestinal epithelial cells. Pedestal formation in vitro requires translocation of bacterial effectors into the host cell, including Tir, an EHEC receptor, and EspFU, which increases the efficiency of actin assembly initiated by Tir. While inactivation of espF U does not alter colonization in two reservoir hosts, we utilized two disease models to explore the significance of EspFU-promoted actin pedestal formation. EHECΔ espF U efficiently colonized the rabbit intestine during co-infection with wild-type EHEC, but co-infection studies on cultured cells suggested that EspFU produced by wild-type bacteria might have rescued the mutant. Significantly, EHECΔ espF U by itself was fully capable of establishing colonization at 2 days post inoculation but unlike wild type, failed to expand in numbers in the caecum and colon by 7 days. In the gnotobiotic piglet model, an espF U deletion mutant appeared to generate actin pedestals with lower efficiency than wild type. Furthermore, aggregates of the mutant occupied a significantly smaller area of the intestinal epithelial surface than those of the wild type. Together, these findings suggest that, after initial EHEC colonization of the intestinal surface, EspFU may stabilize bacterial association with the epithelial cytoskeleton and promote expansion beyond initial sites of infection. [ABSTRACT FROM AUTHOR]