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. 2014 Nov 8:3:12-7.
doi: 10.1016/j.nmni.2014.10.003. eCollection 2015 Jan.

Prevalence and pathogenicity of binary toxin-positive Clostridium difficile strains that do not produce toxins A and B

C Eckert  1 , A Emirian  2 , A Le Monnier  3 , L Cathala  4 , H De Montclos  5 , J Goret  6 , P Berger  7 , A Petit  8 , A De Chevigny  8 , H Jean-Pierre  9 , B Nebbad  2 , S Camiade  10 , R Meckenstock  11 , V Lalande  12 , H Marchandin  9 , F Barbut  13
Affiliations

Prevalence and pathogenicity of binary toxin-positive Clostridium difficile strains that do not produce toxins A and B

C Eckert et al. New Microbes New Infect. .

Abstract

Clostridium difficile causes antibiotic-associated diarrhoea and pseudomembranous colitis. The main virulence factors of C. difficile are the toxins A (TcdA) and B (TcdB). A third toxin, called binary toxin (CDT), can be detected in 17% to 23% of strains, but its role in human disease has not been clearly defined. We report six independent cases of patients with diarrhoea suspected of having C. difficile infection due to strains from toxinotype XI/PCR ribotype 033 or 033-like, an unusual toxinotype/PCR ribotype positive for CDT but negative for TcdA and TcdB. Four patients were considered truly infected by clinicians and were specifically treated with oral metronidazole. One of the cases was identified during a prevalence study of A(-)B(-)CDT(+) strains. In this study, we screened a French collection of 220 nontoxigenic strains and found only one (0.5%) toxinotype XI/PCR ribotype 033 or 033-like strain. The description of such strains raises the question of the role of binary toxin as a virulence factor and could have implications for laboratory diagnostics that currently rarely include testing for binary toxin.

Keywords: A−B−CDT+ strains; Clostridium difficileI; PCR ribotype 033; binary toxin; diagnostic; toxinotype XI.

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Figures

FIG. 1
FIG. 1
Restriction patterns obtained for A3 amplified fragment of tcdA gene for Clostridium difficile A−B−CDT+ strains isolated from patients compared with reference strains. ND, unrestricted; E., EcoRI digestion. Lanes: 1, DNA ladder (kb); 2, PCR ribotype 027; 3, 542 (reference strain for toxinotype XIa); 4, CD219 (reference strain for toxinotype XIa); 5, strain isolated from patient 1; 6, R11402 (reference strain for toxinotype XIb); 7, strain isolated from patient 2.
FIG. 2
FIG. 2
PCR ribotype of Clostridium difficile A−B−CDT+ strains isolated from patients compared with reference strains. Lanes: 1, DNA ladder (bp); 2, PCR ribotype 027; 3, R11402 (reference strain; toxinotype XIb); 4, patient 2; 5, patient 4; 6, strain isolated in prevalence study; 7, 542 (reference strain; toxinotype XIa); 8, patient 1; 9, CD219 (reference strain; PCR ribotype 033; toxinotype XIa); 10, patient 3; 11, patient 5.
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