title: Defining the Roles of TcdA and TcdB in Localized Gastrointestinal Disease, Systemic Organ Damage, and the Host Response during Clostridium difficile Infections.
abstract: Clostridium difficile is a leading cause of antibiotic-associated diarrhea, a significant animal pathogen, and a worldwide public health burden. Most disease-causing strains secrete two exotoxins, TcdA and TcdB, which are considered to be the primary virulence factors. Understanding the role that these toxins play in disease is essential for the rational design of urgently needed new therapeutics. However, their relative contributions to disease remain contentious. Using three different animal models, we show that TcdA(+) TcdB(-) mutants are attenuated in virulence in comparison to the wild-type (TcdA(+) TcdB(+)) strain, whereas TcdA(-) TcdB(+) mutants are fully virulent. We also show for the first time that TcdB alone is associated with both severe localized intestinal damage and systemic organ damage, suggesting that this toxin might be responsible for the onset of multiple organ dysfunction syndrome (MODS), a poorly characterized but often fatal complication of C. difficile infection (CDI). Finally, we show that TcdB is the primary factor responsible for inducing the in vivo host innate immune and inflammatory responses. Surprisingly, the animal infection model used was found to profoundly influence disease outcomes, a finding which has important ramifications for the validation of new therapeutics and future disease pathogenesis studies. Overall, our results show unequivocally that TcdB is the major virulence factor of C. difficile and provide new insights into the host response to C. difficile during infection. The results also highlight the critical nature of using appropriate and, when possible, multiple animal infection models when studying bacterial virulence mechanisms.
  
  
  OBJECTIVE
  Clostridium difficile is a leading cause of antibiotic-associated diarrhea and an important hospital pathogen. TcdA and TcdB are thought to be the primary virulence factors responsible for disease symptoms of C. difficile infections (CDI). However, the individual contributions of these toxins to disease remain contentious. Using three different animal models of infection, we show for the first time that TcdB alone causes severe damage to the gut, as well as systemic organ damage, suggesting that this toxin might be responsible for MODS, a serious but poorly understood complication of CDI. These findings provide important new insights into the host response to C. difficile during infection and should guide the rational development of urgently required nonantibiotic therapeutics for the treatment of CDI.
authors.affiliation: Department of Microbiology, Monash University, Victoria, Australia.
authors.forename: Glen P
authors.initials: GP
authors.lastname: Carter
authors.affiliation: Department of Microbiology, Monash University, Victoria, Australia.
authors.forename: Anjana
authors.initials: A
authors.lastname: Chakravorty
authors.affiliation: Wellcome Trust Sanger Institute, Hinxton, United Kingdom.
authors.forename: Tu Anh
authors.initials: TA
authors.lastname: Pham Nguyen
authors.affiliation: Department of Microbiology, Monash University, Victoria, Australia.
authors.forename: Steven
authors.initials: S
authors.lastname: Mileto
authors.affiliation: Wellcome Trust Sanger Institute, Hinxton, United Kingdom.
authors.forename: Fernanda
authors.initials: F
authors.lastname: Schreiber
authors.affiliation: Department of Microbiology, Monash University, Victoria, Australia.
authors.forename: Lucy
authors.initials: L
authors.lastname: Li
authors.affiliation: Department of Microbiology, Monash University, Victoria, Australia.
authors.forename: Pauline
authors.initials: P
authors.lastname: Howarth
authors.affiliation: Wellcome Trust Sanger Institute, Hinxton, United Kingdom.
authors.forename: Simon
authors.initials: S
authors.lastname: Clare
authors.affiliation: Department of Microbiology, Monash University, Victoria, Australia.
authors.forename: Bliss
authors.initials: B
authors.lastname: Cunningham
authors.forename: Susan P
authors.initials: SP
authors.lastname: Sambol
authors.forename: Adam
authors.initials: A
authors.lastname: Cheknis
authors.forename: Iris
authors.initials: I
authors.lastname: Figueroa
authors.forename: Stuart
authors.initials: S
authors.lastname: Johnson
authors.forename: Dale
authors.initials: D
authors.lastname: Gerding
authors.affiliation: Department of Microbiology, Monash University, Victoria, Australia.
authors.forename: Julian I
authors.identifier: http://orcid.org/0000-0003-2126-7209
authors.initials: JI
authors.lastname: Rood
authors.affiliation: Wellcome Trust Sanger Institute, Hinxton, United Kingdom.
authors.forename: Gordon
authors.initials: G
authors.lastname: Dougan
authors.affiliation: Wellcome Trust Sanger Institute, Hinxton, United Kingdom.
authors.forename: Trevor D
authors.initials: TD
authors.lastname: Lawley
authors.affiliation: Department of Microbiology, Monash University, Victoria, Australia Dena.Lyras@monash.edu.
authors.forename: Dena
authors.initials: D
authors.lastname: Lyras
mesh_terms: D000818:Animals; D001426:Bacterial Proteins / Q000235:genetics / Q000276:immunology / Q000633:toxicity*; D001427:Bacterial Toxins / Q000235:genetics / Q000276:immunology / Q000633:toxicity*; D001896:Boron Compounds; D016360:Clostridioides difficile / Q000276:immunology / Q000472:pathogenicity*; D003015:Clostridium Infections / Q000139:chemically induced / Q000276:immunology / Q000382:microbiology* / Q000473:pathology*; D004195:Disease Models, Animal; D004768:Enterotoxins / Q000235:genetics / Q000276:immunology / Q000633:toxicity*; D005767:Gastrointestinal Diseases / Q000139:chemically induced / Q000276:immunology / Q000382:microbiology / Q000473:pathology; D055786:Gene Knockout Techniques; D009102:Multiple Organ Failure / Q000139:chemically induced / Q000276:immunology / Q000382:microbiology / Q000473:pathology; D014774:Virulence; D037521:Virulence Factors / Q000235:genetics / Q000276:immunology / Q000633:toxicity
chemical_list: D001426:Bacterial Proteins; D001427:Bacterial Toxins; D001896:Boron Compounds; D004768:Enterotoxins; D037521:Virulence Factors; C041348:tcdA protein, Clostridium difficile; C031815:toxB protein, Clostridium difficile; C057908:trimethylaminocarboxyldihydroboran