Dataset Information


Microarray Analysis of Acid-Stress Induced Changes in EHEC O157:H7

ABSTRACT: While significant advances have been made in EHEC pathogenesis, we still do not fully understand the impact of environmental stress on EHEC virulence. During the course of infection, EHEC must evade or overcome several biological barriers, the first of which is the gastric acidity encountered during passage through the stomach. EHEC is remarkable in its ability to tolerate this acidity. There are four different acid resistance systems that provide E. coli O157:H7 protection against exposure to low pH (2-2.5). Interestingly, EHEC uses these acid resistance systems differentially for survival in foods versus the bovine intestinal tract. The glutamate-dependent acid-resistance system is thought to offer the best protection below pH 3. Since the infectious dose of EHEC is so low (50-100 organisms), acid resistance becomes an important virulence trait. Studies of EHEC response to acid stress have focused primarily on levels of acid tolerance and the molecular basis of tolerance. However, the impact of acid stress on EHEC virulence is less well understood. In the related pathogen, EPEC, the plasmid-encoded regulator, Per, that regulates expression of many EPEC virulence factors, is regulated negatively at pH 5.5 and positively at pH 8.0, suggesting that virulence gene expression is repressed during mild acid stress and enhanced in alkaline pH typical of the small intestine. Expression of EPEC type III secreted factors involved in A/E lesion formation has been shown to be influenced by factors including culture media, iron and calcium levels. Protein secretion was inhibited at pH 6 and 8. In a third study, a gadE (encoding acid resistance regulator) mutation resulted in increased adhesion of E.coli O157:H7 to colonic epithelial cells, suggesting negative regulation of one or more adhesins. Other studies have reported that shiga toxin production is sensitive to culture conditions including pH. However, there are no studies of EHEC virulence changes after more severe acid stress nor studies linking stressed EHEC virulence phenotype with transcriptional changes. The goal of this study was to determine how acid stress affects EHEC virulence properties and through microarray analysis, define the genetic basis for these changes. Understanding how acid stress modulates the virulence potential of this pathogen is essential for delineating the pathogenesis of disease caused by EHEC infection and may offer novel approaches to prevent and treat EHEC infections. Bacteria were grown in LB broth overnight, then subcultured into DMEM and grown at 37C, 5%Co2. Bacteria were then subjected to one of three acid stress protocols: 1) UA30: growth in DMEM pH 7.4 followed by growth in DMEM pH 3.0 for 30 minutes; 2) AA30: growth in DMEM pH 5.0 (adaptation) followed by growth in DMEM pH 3.0; 3) UA15: growth in DMEM pH 7.4 followed by growth in DMEM pH 3.0 for 15 minutes. DMEM was supplemented with 25 mM MES (pH 5.0) and in the case of the control (unadapted, unshocked) 25 mM MOPS (pH 7.4) and the adaptation step was again carried out at 37C and 5% CO2. Acid shocking was done at pH 3.0 (unbuffered) at room temperature for all treatments

ORGANISM(S): Escherichia coli  

SUBMITTER: Debora Barnett Foster   Belinda House  Richard W Mair  Nita Prayitano  Victor Gannon  Dennis G Cvitkovitch  Lynne Que  Debora Foster  Julianne V Kus 

PROVIDER: E-GEOD-14069 | ArrayExpress | 2010-05-16



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Acid-stress-induced changes in enterohaemorrhagic Escherichia coli O157 : H7 virulence.

House B B   Kus J V JV   Prayitno N N   Mair R R   Que L L   Chingcuanco F F   Gannon V V   Cvitkovitch D G DG   Barnett Foster D D  

Microbiology (Reading, England) 20090604 Pt 9

Enterohaemorrhagic Escherichia coli (EHEC) O157 : H7 is naturally exposed to a wide variety of stresses including gastric acid shock, and yet little is known about how this stress influences virulence. This study investigated the impact of acid stress on several critical virulence properties including survival, host adhesion, Shiga toxin production, motility and induction of host-cell apoptosis. Several acid-stress protocols with relevance for gastric passage as well as external environmental ex  ...[more]

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