Escherichia coliO157:H7 Survives within Human Macrophages: Global Gene Expression Profile and Involvement of the Shiga Toxins

Abstract

Escherichia coli O157:H7 is an important food-borne pathogen that specifically binds to the follicle-associated epithelium in the intestine, which rapidly brings this bacterial pathogen in contact with underlying human macrophages. Very little information is available about the interaction between E. coli O157:H7 and human macrophages. We evaluated the uptake and survival of strain EDL933 during infection of human macrophages. Surprisingly, EDL933 survived and multiplied in human macrophages at 24 h postinfection. The global gene expression profile of this pathogen during macrophage infection was determined. Inside human macrophages, upregulation of E. coli O157:H7 genes carried on O islands (such as pagC, the genes for both of the Shiga toxins, and the two iron transport system operons fit and chu) was observed. Genes involved in acid resistance and in the SOS response were upregulated. However, genes of the locus of enterocyte effacement or genes involved in peroxide resistance were not differentially expressed. Many genes with putative or unknown functions were upregulated inside human macrophages and may be newly discovered virulence factors. As the Shiga toxin genes were upregulated in macrophages, survival and cytotoxicity assays were performed with isogenic Shiga toxin mutants. The initial uptake of Shiga toxins mutants was higher than that of the wild type; however, the survival rates were significantly lower at 24 h postinfection. Thus, Shiga toxins are implicated in the interaction between E. coli O157:H7 and human macrophages. Understanding the molecular mechanisms used by E. coli to survive within macrophages may help in the identification of targets for new therapeutic agents.Enterohemorragic Escherichia coli (EHEC) causes an acute gastroenteritis, bloody diarrhea, and hemorrhagic colitis. Severe complications develop in up to 10% of cases, including the hemolytic-uremic syndrome, which can be fatal (45,56). EHEC strains share their genetic backbone with the laboratory strain K-12 and also contain 1.34 Mb of extra genetic material called O islands (OI) (46). In the EHEC strain EDL933 (O157: H7), 177 OI were identified; some of them harbor genes for important known virulence factors of EHEC, such as the locus of enterocyte effacement (LEE) and two different Shiga toxins, Stx1 and Stx2. Following the ingestion of contaminated food or water, EHEC enters the gastrointestinal tract, survives the acidic conditions of the stomach, and is released in the intestine. Adhesion of the bacteria to the intestinal wall is the first step in establishing infection. The LEE encodes a type III secretion system (T3SS) that injects effectors in host epithelial cells, creating an intimate binding, involving actin rearrangement and microvillus effacement, which results in the pathological lesions called attaching and effacing lesions (40, 52). In the large intestine, EHEC specifically adheres to the follicleassociated epithelium of Peyer's patches (47). Binding at the follicle-associated epithelium results in the rapid co...

Construction of a novel bioluminescent reporter system for investigating Shiga toxin expression of enterohemorrhagic Escherichia coli

“…These results were consistent with those of a transcriptional study that used microarray analysis (Poirier et al, 2008). Since genes related to the SOS response in EHEC were upregulated within macrophages (Poirier et al, 2008), Stx2 production in EHEC might be increased within macrophages. However, the mechanism underlying upregulation of Stx1 production in EHEC within macrophages remains unclear.…”

Subtilase Cytotoxin Enhances Escherichia coli Survival in Macrophages by Suppression of Nitric Oxide Production through the Inhibition of NF-κB Activation

“…A number of pathogenic bacteria have developed a variety of mechanisms to evade host defense mechanisms and enhance their virulence (44). Previous studies showed that Stx or other bacterial factors of STEC, such as EspA, B, and D, downregulate NF-B activation (15,18).…”

Verotoxin 2 Enhances Adherence of Enterohemorrhagic Escherichia coli O157:H7 to Intestinal Epithelial Cells and Expression of β1-Integrin by IPEC-J2 Cells

“…Gb3 synthesis is also induced by cytokines, including tumor necrosis factor (TNF), that are induced by VT2 and lipopolysaccharide (LPS) during infection (8,17). Binding of VT to Gb3 in endothelial cells further increases the expression of Gb3 and exacerbates the disease process by EHEC O157:H7 (16,20). Binding of VT to Gb3 may indirectly promote EHEC O157:H7 adherence, because it represses antibacterial peptide secretion and host cellular immune response (7,23).…”