Prevalence of binary-toxin genes (cdtA and cdtB) among clinical strains of Clostridium difficile isolated from diarrheal patients in Iran

In this study we investigated the prevalence of binary toxin genes, cdtA and cdtB, in clinical isolates of C. difficile from hospitalized patients with diarrhea. C. difficile binary toxin (CDT) is an action-specific ADP-ribosyltransferase that is produced by some strains of C. difficile. Co-expression of this toxin with tcdA and tcdB can lead to more severe disease in CDI patients. Totally, 930 patients suspected of having CDI was included in this study. All samples were treated with methanol and cultured on selective C. difficile agar plates. The C. difficile isolates were further identified by PCR. Presence of tcdA, tcdB, cdtA, and cdtB genes among the strains were examined by PCR. Analysis of the PCR results showed a prevalence of 85.2% (144/169) for toxigenic C. diffidile. Toxin genotyping of the strains for tcdA and tcdB genes revealed the toxin profiles of A+B+, A+B-, A-B+ accounting for 86.1% (124/144), 7.6% (11/144), 6.2% (9/144) among the strains, respectively. Totally, 12.4% (21/169) of the C. difficile strains were binary toxin-positive. cdtA-B+, cdtA+B+ and cdtA+B- were detected in 43% (9/21), 38% (8/21) and 19% (4/21) of the strains, respectively. Interestingly, 12% (3/25) of nontoxigenic C. difficile strains (tcdA-B-) had either cdtA+B+ or cdtA-B+ profiles. This is the first report for the prevalence of binary toxin genes in C. difficile strains isolated from Iran. Further studies are required to investigate the exact role of binary toxins in the pathogenesis of C. difficile particularly in patients with chronic diarrhea among Iranian populations.