Commensal E. coli Stx2 lysogens produce high levels of phages after spontaneous prophage induction.

Hildegunn Iversen,Trine M L' Abã©E-Lund,Toril Lindbã¤Ck,Marina Aspholm,Lotte P S Arnesen

doi:10.3389/fcimb.2015.00005

Hildegunn Iversen, Trine M L' Abã©E-Lund + Show 3 more

Open Access

https://doi.org/10.3389/fcimb.2015.00005

Copy DOI

Abstract

Enterohemorrhagic E. coli (EHEC) is a food-borne pathogen that causes disease ranging from uncomplicated diarrhea to life-threatening hemolytic uremic syndrome (HUS) and nervous system complications. Shiga toxin 2 (Stx2) is the major virulence factor of EHEC and is critical for development of HUS. The genes encoding Stx2 are carried by lambdoid bacteriophages and the toxin production is tightly linked to the production of phages during lytic cycle. It has previously been suggested that commensal E. coli could amplify the production of Stx2-phages and contribute to the severity of disease. In this study we examined the susceptibility of commensal E. coli strains to the Stx2-converting phage ϕ734, isolated from a highly virulent EHEC O103:H25 (NIPH-11060424). Among 38 commensal E. coli strains from healthy children below 5 years, 15 were lysogenized by the ϕ734 phage, whereas lytic infection was not observed. Three of the commensal E. coli ϕ734 lysogens were tested for stability, and appeared stable and retained the phage for at least 10 cultural passages. When induced to enter lytic cycle by H2O2 treatment, 8 out of 13 commensal lysogens produced more ϕ734 phages than NIPH-11060424. Strikingly, five of them even spontaneously (non-induced) produced higher levels of phage than the H2O2 induced NIPH-11060424. An especially high frequency of HUS (60%) was seen among children infected by NIPH-11060424 during the outbreak in 2006. Based on our findings, a high Stx2 production by commensal E. coli lysogens cannot be ruled out as a contributor to the high frequency of HUS during this outbreak.

Highlights

Enterohemorrhagic Escherichia coli (EHEC) causes disease with manifestations ranging from mild diarrhea to severe illness comprising hemorrhagic colitis (HC) (Riley et al, 1983) and hemolytic uremic syndrome (HUS) (Karmali et al, 1983, 1985)
There is increasing evidence that commensal E. coli strains infected with Shiga toxin 2 (Stx2)-converting phages can contribute to Shiga toxin (Stx) production in the intestine, and thereby increase the pathogenicity during EHEC infection (Gamage et al, 2003, 2004, 2006; Toth et al, 2003; Cornick et al, 2006)
We provide results which suggest that some commensal E. coli have the potential to be significant producers of Stx and could have contributed to the extraordinary pathogenicity of strain NIPH-11060424 during the Norwegian 2006 EHEC outbreak

Summary

Introduction

Enterohemorrhagic Escherichia coli (EHEC) causes disease with manifestations ranging from mild diarrhea to severe illness comprising hemorrhagic colitis (HC) (Riley et al, 1983) and hemolytic uremic syndrome (HUS) (Karmali et al, 1983, 1985). EHEC strains possess a range of colonization and virulence factors that facilitate infection and contribute to development of disease. Shiga toxin (Stx) is recognized as one of the main virulence factors in enterohemorrhagic disease caused by E. coli and all EHEC strains produce one or both of the Shiga toxins Stx and Stx (Scotland et al, 1985). The Stx induced cell damage appears to be central in the pathogenic events leading to HUS and occasionally chronic kidney disease (Obrig, 2010; Obrig and Karpman, 2012)

Methods

Results

Conclusion