Horizontal gene transfer converts non-toxigenic Clostridium difficile strains into toxin producers

Michael S.M Brouwer,Rachel J Williams,Peter Mullany,Adam P Roberts,Haitham Hussain,Elaine Allan

doi:10.1038/ncomms3601

Michael S.M Brouwer, Rachel J Williams + Show 4 more

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https://doi.org/10.1038/ncomms3601

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Abstract

Clostridium difficile is a major nosocomial pathogen and the main causative agent of antibiotic-associated diarrhoea. The organism produces two potent toxins, A and B, which are its major virulence factors. These are chromosomally encoded on a region termed the pathogenicity locus (PaLoc), which also contains regulatory genes, and is absent in non-toxigenic strains. Here we show that the PaLoc can be transferred from the toxin-producing strain, 630Δerm, to three non-toxigenic strains of different ribotypes. One of the transconjugants is shown by cytotoxicity assay to produce toxin B at a similar level to the donor strain, demonstrating that a toxigenic C. difficile strain is capable of converting a non-toxigenic strain to a toxin producer by horizontal gene transfer. This has implications for the treatment of C. difficile infections, as non-toxigenic strains are being tested as treatments in clinical trials.

Highlights

Clostridium difficile is a major nosocomial pathogen and the main causative agent of antibioticassociated diarrhoea
To determine whether genetic elements were cotransferred in the absence of direct selection when transfer of CTn1 was selected, we initially investigated nine CD37 transconjugants containing CTn1::ermB (an erythromycin-resistant derivative of CTn1) by PCR and subsequent DNA sequencing
pathogenicity locus (PaLoc)-containing transconjugants were obtained at a frequency of 7.5 Â 10 À 9 transconjugants per donor (s.d. 1⁄4 4.2 Â 10 À 9), comparable to transfer frequencies previously reported for other conjugative transposons (CTns) that are transferred between these strains[9]

Summary

Introduction

Clostridium difficile is a major nosocomial pathogen and the main causative agent of antibioticassociated diarrhoea. The organism produces two potent toxins, A and B, which are its major virulence factors These are chromosomally encoded on a region termed the pathogenicity locus (PaLoc), which contains regulatory genes, and is absent in non-toxigenic strains. One of the transconjugants is shown by cytotoxicity assay to produce toxin B at a similar level to the donor strain, demonstrating that a toxigenic C. difficile strain is capable of converting a non-toxigenic strain to a toxin producer by horizontal gene transfer. The organism produces two potent toxins, A and B, which disrupt the gut epithelium and are the major virulence factors of this organism[3,4] Both toxins are encoded on the pathogenicity locus (PaLoc), a 19.6-kb chromosomal region that encodes potential transcriptional regulators and a holin-like protein. We demonstrate that the PaLoc can be transferred to CD37, which results in this non-toxigenic strain being converted to a toxin producer

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