The Anti-Sigma Factor TcdC Modulates Hypervirulence in an Epidemic BI/NAP1/027 Clinical Isolate of Clostridium difficile

Abstract

Nosocomial infections are increasingly being recognised as a major patient safety issue. The modern hospital environment and associated health care practices have provided a niche for the rapid evolution of microbial pathogens that are well adapted to surviving and proliferating in this setting, after which they can infect susceptible patients. This is clearly the case for bacterial pathogens such as Methicillin Resistant Staphylococcus aureus (MRSA) and Vancomycin Resistant Enterococcus (VRE) species, both of which have acquired resistance to antimicrobial agents as well as enhanced survival and virulence properties that present serious therapeutic dilemmas for treating physicians. It has recently become apparent that the spore-forming bacterium Clostridium difficile also falls within this category. Since 2000, there has been a striking increase in C. difficile nosocomial infections worldwide, predominantly due to the emergence of epidemic or hypervirulent isolates that appear to possess extended antibiotic resistance and virulence properties. Various hypotheses have been proposed for the emergence of these strains, and for their persistence and increased virulence, but supportive experimental data are lacking. Here we describe a genetic approach using isogenic strains to identify a factor linked to the development of hypervirulence in C. difficile. This study provides evidence that a naturally occurring mutation in a negative regulator of toxin production, the anti-sigma factor TcdC, is an important factor in the development of hypervirulence in epidemic C. difficile isolates, presumably because the mutation leads to significantly increased toxin production, a contentious hypothesis until now. These results have important implications for C. difficile pathogenesis and virulence since they suggest that strains carrying a similar mutation have the inherent potential to develop a hypervirulent phenotype.

Genome Characterization of a Novel Binary Toxin-Positive Strain of <em>Clostridium difficile</em> and Comparison with the Epidemic 027 and 078 Strains

“…Further analysis needs to be performed to determine whether the toxin-yielding profile of the ST201 strain is closer to the 027 strain or to the 078 strain. For the toxin expression regulating genes, the tcdC gene is proposed to be a negative regulator for the toxin production, and the mutations within tcdC is observed to contribute to the toxin-production of some 027 strains [46,47]. In our study, two main kinds of mutations were found within the tcdC gene ST201 carried by the ST201 strains compared to strain 630.…”

Variations in Virulence and Molecular Biology among Emerging Strains of Clostridium difficile

“…Studies involving full-length TcdC expressed from a plasmid conjugated into a TcdC-negative strain of C. difficile found that intact functional TcdC can cause the organism to produce smaller-than-normal amounts of toxin (184). Moreover, this tcdC ϩ strain was found to be attenuated in virulence relative to the parent strain.…”

The potential for emerging therapeutic options forClostridium difficileinfection

“…11 It is noteworthy that earlier studies investigating the role of TcdC were in vitro investigations. 12,13 The in vivo mechanisms of this protein had remained largely unclear however. A recent in vivo study has now indicated that TcdC may not actually play a key role in C. difficile virulence.…”

“…16 Interestingly however, using isogenic strains of C. difficile, Carter et al showed that a naturally occurring mutation in tcdC is responsible for the hypervirulence of epidemic C. difficile isolates. 12 Thus, the precise mechanisms of action of TcdC in vivo have yet to be definitively ascertained.…”