The Salmonella Typhi hlyE gene plays a role in invasion of cultured epithelial cells and its functional transfer to S. Typhimurium promotes deep organ infection in mice

Programa de Doctorado en Ciencias Biológicas, Pontificia Universidad Católica de Chile, Alameda 340, Santiago, Chile.
Research in Microbiology (Impact Factor: 2.71). 06/2008; 159(4):279-87. DOI: 10.1016/j.resmic.2008.02.006
Source: PubMed


Comparison of genome sequences of Salmonella enterica serovars Typhi and Typhimurium reveals that S. Typhi has a small 2.3kb genomic island missing in S. Typhimurium, designated Salmonella pathogenicity island 18 (SPI-18), which includes two potential genes. One of these, hlyE, encodes a hemolysin related to the Escherichia coli K12 HlyE hemolysin. PCR assays show that SPI-18 is present in S. Typhi and in many other, but not all, serovars of S. enterica subsp. enterica belonging to the SARB collection. HlyE activity cannot be detected in S. Typhi by means of standard plate assays. Nevertheless, we were able to reveal this activity upon lysis of bacterial cells with phages, in the presence of ampicillin, and in a ompA genetic background, conditions that compromise the integrity of the bacterial envelope. Almost all serovars of the SARB collection shown to cause systemic infections in humans have SPI-18 and hlyE and express an active hemolysin revealed upon bacterial envelope destabilization. S. Typhi hlyE mutants are impaired in invasion of human epithelial cells in vitro, and its heterologous expression in S. Typhimurium improves the colonization of deep organs in mice, demonstrating that the HlyE hemolysin is a new virulence determinant.

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Available from: Juan A Fuentes, Jul 10, 2014
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    • "Human infections by S. Typhi cause a specific antibody response to HlyE, indicating effective toxin production during the normal infective cycle [13]. Moreover, heterologous expression of S. Typhi hlyE in S. Typhimurium improves the colonization of deep organs in mice [10]. "
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    ABSTRACT: Background SPI-18 is a pathogenicity island found in some Salmonella enterica serovars, including S. Typhi. SPI-18 harbors two ORFs organized into an operon, hlyE and taiA genes, both implicated in virulence. Regarding the hlyE regulation in S. Typhi, it has been reported that RpoS participates as transcriptional up-regulator under low pH and high osmolarity. In addition, CRP down-regulates hlyE expression during exponential growth. Previously, it has been suggested that there is another factor related to catabolite repression, different from CRP, involved in the down-regulation of hlyE. Moreover, PhoP-dependent hlyE up-regulation has been reported in bacteria cultured simultaneously under low pH and low concentration of Mg2+. Nevertheless, the relative contribution of each environmental signal is not completely clear. In this work we aimed to better understand the regulation of hlyE in S. Typhi and the integration of different environmental signals through global regulators. Results We found that Fis participates as a CRP-independent glucose-dependent down-regulator of hlyE. Also, Fis and CRP seem to exert the repression over hlyE through down-regulating rpoS. Moreover, PhoP up-regulates hlyE expression via rpoS under low pH and low Mg2+ conditions. Conclusions All these results together show that, at least under the tested conditions, RpoS is the central regulator in the hlyE regulatory network, integrating multiple environmental signals and global regulators.
    Full-text · Article · May 2014 · BMC Microbiology
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    • "OmpA is a key regulator of bacterial osmotic homeostasis modulating the permeability and integrity of the outer membrane in E. coli [43]. The predicted sequences of S. Typhi and E. coli OmpA proteins are nearly (>90%) identical [44]. In S. Typhi, OmpA is crucial for maintaining envelope integrity and preventing hemolysis through MV secretion [44]. "
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    ABSTRACT: Salmonella enterica serovar Typhi (S. Typhi) is a human-specific pathogen that causes typhoid fever. In this study, we constructed Δ ygaE mutant and a microarray was performed to investigate the role of ygaE in regulation of gene expression changes in response to hyperosmotic stress in S. Typhi. qRT-PCR was performed to validate the microarray results. Our data indicated that ygaE was the repressor of gab operon in S. Typhi as in Escherichia coli (E. coli), though the sequence of ygaE is totally different from gabC (formerly ygaE) in E. coli. OmpF, OmpC, and OmpA are the most abundant out membrane proteins in S. Typhi. Here we report that YgaE is a repressor of both OmpF and OmpC at the early stage of hyperosmotic stress. Two-dimensional electrophoresis was applied to analyze proteomics of total proteins in wild-type strain and Δ ygaE strain and we found that YgaE represses the expression of OmpA at the late stage of hyperosmotic stress. Altogether, our results implied that YgaE regulates out membrane proteins in a time-dependent manner under hyperosmotic stress in S. Typhi.
    Full-text · Article · Jan 2014 · The Scientific World Journal
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    • "In addition to the stress defense systems, we found that the enteric strain-specific gene set included hylE, which encodes the pore-forming toxin involved in invasion of epithelial cells [20], [21]. A homologous gene is also found in other pathogenic strains such as Shigella flexneri and Salmonella typhi [22]. "
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    ABSTRACT: Our understanding of the Escherichia genus is heavily biased toward pathogenic or commensal isolates from human or animal hosts. Recent studies have recovered Escherichia isolates that persist, and even grow, outside these hosts. Although the environmental isolates are typically phylogenetically distinct, they are highly related to and phenotypically indistinguishable from their human counterparts, including for the coliform test. To gain insights into the genomic diversity of Escherichia isolates from diverse habitats, including freshwater, soil, animal, and human sources, we carried out comparative DNA-DNA hybridizations using a multi-genome E. coli DNA microarray. The microarray was validated based on hybridizations with selected strains whose genome sequences were available and used to assess the frequency of microarray false positive and negative signals. Our results showed that human fecal isolates share two sets of genes (n>90) that are rarely found among environmental isolates, including genes presumably important for evading host immune mechanisms (e.g., a multi-drug transporter for acids and antimicrobials) and adhering to epithelial cells (e.g., hemolysin E and fimbrial-like adhesin protein). These results imply that environmental isolates are characterized by decreased ability to colonize host cells relative to human isolates. Our study also provides gene markers that can distinguish human isolates from those of warm-blooded animal and environmental origins, and thus can be used to more reliably assess fecal contamination in natural ecosystems.
    Full-text · Article · Oct 2012 · PLoS ONE
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