Decrease in Shiga toxin expression using a minimal inhibitory concentration of rifampicin followed by bactericidal gentamicin treatment enhances survival of Escherichia coli O157:H7-infected BALB/c mice

Elias A Rahal,Ahmad Sabra,Alexander M Abdelnoor,Ghassan M Matar,Natalie Kazzi

doi:10.1186/1476-0711-10-34

Abstract

BackgroundTreatment of Escherichia coli O157:H7 infections with antimicrobial agents is controversial due to an association with potentially fatal sequelae. The production of Shiga toxins is believed to be central to the pathogenesis of this organism. Therefore, decreasing the expression of these toxins prior to bacterial eradication may provide a safer course of therapy.MethodsThe utility of decreasing Shiga toxin gene expression in E. coli O157:H7 with rifampicin prior to bacterial eradication with gentamicin was evaluated in vitro using real-time reverse-transcription polymerase chain reaction. Toxin release from treated bacterial cells was assayed for with reverse passive latex agglutination. The effect of this treatment on the survival of E. coli O157:H7-infected BALB/c mice was also monitored.ResultsTranscription of Shiga toxin-encoding genes was considerably decreased as an effect of treating E. coli O157:H7 in vitro with the minimum inhibitory concentration (MIC) of rifampicin followed by the minimum bactericidal concentration (MBC) of gentamicin (> 99% decrease) compared to treatment with gentamicin alone (50-75% decrease). The release of Shiga toxins from E. coli O157:H7 incubated with the MIC of rifampicin followed by addition of the MBC of gentamicin was decreased as well. On the other hand, the highest survival rate in BALB/c mice infected with E. coli O157:H7 was observed in those treated with the in vivo MIC equivalent dose of rifampicin followed by the in vivo MBC equivalent dose of gentamicin compared to mice treated with gentamicin or rifampicin alone.ConclusionsThe use of non-lethal expression-inhibitory doses of antimicrobial agents prior to bactericidal ones in treating E. coli O157:H7 infection is effective and may be potentially useful in human infections with this agent in addition to other Shiga toxin producing E. coli strains.

Highlights

Treatment of Escherichia coli O157:H7 infections with antimicrobial agents is controversial due to an association with potentially fatal sequelae
Effect of in vitro treatment with antimicrobial agents on toxin expression in E. coli O157:H7 Multiple rifampicin and gentamicin treatment regimens were used to assess the effect of these agents on the expression of Shiga toxin 1 (Stx1) and Shiga toxin 2 (Stx2) encoding genes, stx1 and stx2, in E. coli O157:H7
Real-time reverse-transcription polymerase chain reaction (RT-PCR) showed that the stx1 and stx2 genes were expressed in the E. coli O157:H7 strain employed when incubated in antimicrobial agent-free broth (Figure 1)

Summary

Introduction

Treatment of Escherichia coli O157:H7 infections with antimicrobial agents is controversial due to an association with potentially fatal sequelae. Several virulence factors contribute to the pathogenicty of E. coli O157:H7 with the production of Shiga toxins (Stxs) being at the epicenter of the infectious process These toxins consist of two major groups: Stx, which is nearly identical to the toxin of Shigella dysenteriae type 1, and Stx, which shares less than 55% amino acid sequence with Stx1 [7,8,9]. Another virulence factor is the locus of enterocyte effacement (LEE) which contains genes required for the production of the attaching and effacing (A/E) lesions that accompany E. coli O157: H7 infection [10]. The Shiga toxins have been implicated in contributing to the process of intestinal colonization [11]

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Conclusion