Abstract

Enterohemorrhagic Escherichia coli (EHEC) O157:H7 is a major foodborne pathogen causing hemorrhagic colitis and hemolytic-uremic syndrome. The role of EHEC O157:H7-enterohemolysin (Ehx) in the pathogenesis of infections remains poorly defined. In this study, we used gene deletion and complement methods to confirm its putative functions. Results demonstrated that, in THP-1 cells, EHEC O157:H7-Ehx is associated with greater production of extracellular interleukin (IL)-1β than other cytokines. The data also showed that EHEC O157:H7-Ehx contributed to cytotoxicity in THP-1 cells, causing the release of lactate dehydrogenase (LDH). Although we observed a positive correlation between IL-1β production and cytotoxicity in THP-1 cells infected with different EHEC O157:H7 strains, our immunoblot results showed that the majority of IL-1β in the supernatant was mature IL-1β and not the pro-IL-1β that can be released after cell death. However, EHEC O157:H7-Ehx had no detectable effect on biologically inactive pro-IL-1β at the mRNA or protein synthesis levels. Neither did it affect the expression of apoptosis-associated speck-like protein containing a CARD (ASC), caspase-1, or NOD-like receptor family pyrin domain containing 3 (NLRP3). RNA interference experiments showed that EHEC O157:H7-induced IL-1β production required the involvement of ASC, caspase-1, and NLRP3 expression in THP-1 cells. Our results demonstrate that Ehx plays a crucial role in EHEC O157:H7-induced IL-1β production and its cytotoxicity to THP-1 cells. NLRP3 inflammasome activation is also involved in EHEC O157:H7-stimulated IL-1β release.

Highlights

  • Enterohemorrhagic Escherichia coli (EHEC) serotype O157:H7 is a major foodborne pathogen

  • More studies focused on the better-known virulence factors of EHEC O157:H7 that contribute to the inflammatory response, such as Shiga toxins (Stxs), the locus of enterocyte effacement (LEE) pathogenicity island and flagellin [4,5,6,7,8]

  • It is likely that the EHEC-Ehx is expressed during human infection and subsequent disease, as patients suffering from O157-associated hemolytic-uremic syndrome (HUS) produce specific EHEC-Ehx antibodies in almost all cases [18]

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Summary

Introduction

Enterohemorrhagic Escherichia coli (EHEC) serotype O157:H7 is a major foodborne pathogen. It causes diarrhea, hemorrhagic colitis, and hemolytic-uremic syndrome (HUS), which can be lifethreatening [1]. EHEC O157:H7 can come into contact with underlying human macrophages through the follicle-associated epithelium of Peyer’s patches [2]. Previous studies have shown that tumor necrosis factor-a (TNF-a) and interleukin (IL)-1b produced by infected macrophages can contribute to the severe inflammation associated with HUS [3]. The role of virulence factors in the macrophage-associated inflammatory response to EHEC O157:H7 infection remains to be determined

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