Bacteriophage-Mediated Toxin Gene Regulation in Clostridium difficile

Abstract

Clostridium difficile has been identified as the most important single identifiable cause of nosocomial antibiotic-associated diarrhea and colitis. Virulent strains of C. difficile produce two large protein toxins, toxin A and toxin B, which are involved in pathogenesis. In this study, we examined the effect of lysogeny by ⌽CD119 on C. difficile toxin production. Transcriptional analysis demonstrated a decrease in the expression of pathogenicity locus (PaLoc) genes tcdA, tcdB, tcdR, tcdE, and tcdC in ⌽CD119 lysogens. During this study we found that repR, a putative repressor gene of ⌽CD119, was expressed in C. difficile lysogens and that its product, RepR, could downregulate tcdA::gusA and tcdR::gusA reporter fusions in Escherichia coli. We cloned and purified a recombinant RepR containing a C-terminal six-His tag and documented its binding to the upstream regions of tcdR in C. difficile PaLoc and in repR upstream region in ⌽CD119 by gel shift assays. DNA footprinting experiments revealed similarities between the RepR binding sites in tcdR and repR upstream regions. These findings suggest that presence of a CD119-like temperate phage can influence toxin gene regulation in this nosocomially important pathogen.Clostridium difficile, a gram-positive, anaerobic, spore-forming bacterium, has been identified as one of the major causative agents of antibiotic-associated diarrhea and pseudomembranous colitis. C. difficile produces toxins A and B that damage intestinal mucosa and cause fluid accumulation in the colon (1). The toxin genes tcdA and tcdB, along with accessory genes tcdR, tcdC, and tcdE, are part of a 19.6-kb pathogenicity locus (PaLoc). Toxin genes tcdA and tcdB are positively regulated by TcdR (previously TxeR) (27), and tcdC is involved in the negative regulation of toxin genes (16,29). In pathogenic C. difficile strains, the PaLoc is present at identical locations in the chromosome, whereas it is completely absent in nontoxinogenic strains. This observation has led to the suggestion that the presence of the toxin gene cluster may be associated with a transposable genetic element (3). In other clostridial species, toxins are known to be encoded by mobile genetic elements such as bacteriophages and plasmids (6,9,10,31).Following publication of the genome of ⌽CD119 (15), the genome of a second C. difficile temperate phage (⌽C2, a member of the Myoviridae) was published (13). More recently, eight temperate phages were characterized from six different C. difficile isolates, including the hypervirulent strain responsible for a multi-institutional outbreak (NAP1/027 or QCD-32g58) (11). In addition, the multidrug-resistant C. difficile strain CD630 was found to harbor two highly related prophages (13, 39) as part of its mosaic genome, where nearly 11% is made of mobile genetic elements. Thus, it appears that C. difficile strains often harbor temperate phage(s) as part of their genetic makeup. No direct evidence of lysogenic conversion of a nontoxinogenic C. difficile strain to toxin production was shown. However...

Prophage-Stimulated Toxin Production in Clostridium difficile NAP1/027 Lysogens

“…Previous reports have shown that toxin production in C. difficile can be affected by some prophages (14,18). In order to test whether CD38-2 could influence toxin production in C. difficile, we infected the host isolate CD274, which is a representative member of the hypervirulent strain BI/NAP1/027, to create lysogens.…”

“…So far, C. difficile phages have not been found to encode proven virulence factors or to convert nontoxigenic C. difficile isolates into toxin-producing lysogens (15,17,20,34). Nevertheless, two recent studies suggest that phages may somehow contribute to the regulation of toxin production in C. difficile (14,18), but the clear lack of data regarding phages of C. difficile makes it difficult to appreciate the real impact of prophages on C. difficile lifestyle and virulence.…”

Binary toxin locus analysis in Clostridium difficile

“…Few studies investigating gene expression in C. difficile have been performed (Gerber et al, 2008;Govind et al, 2009;Karlsson et al, 2008) and, as a result, little is known about the regulation of genes, virulence-related or otherwise. With respect to the binary toxin, Carter et al (2007) demonstrated expression of cdtA during the stationary growth phase and expression was significantly reduced in strains with a mutation in cdtR, a gene encoding a putative regulator.…”

The influence of the accessory genome on bacterial pathogen evolution

“…35 In another example, a prophage repressor, RepR, of Clostridium difficile, a common causal agent of nosocomial infections of the intestine, has been found to bind the promoter region of the gene tcdR of the PaLoc pathogenicity island modulating toxin production. 36 In a different strategy that avoids host death, many of the prophage genomes in enterohaemorrhagic E. coli (EHEC) strains and other bacteria are found to be missing genes or have mutations in genes known to be essential for a bacteriophage to enter the lytic cycle and to be horizontally transferred. These bacteriophage remnants were assumed to have in fact lost their ability to be transferred between cells.…”