title: CdtR Regulates TcdA and TcdB Production in Clostridium difficile.
abstract: Clostridium difficile is a global health burden and the leading cause of antibiotic-associated diarrhoea worldwide, causing severe gastrointestinal disease and death. Three well characterised toxins are encoded by this bacterium in two genetic loci, specifically, TcdB (toxin B) and TcdA (toxin A) in the Pathogenicity Locus (PaLoc) and binary toxin (CDT) in the genomically distinct CDT locus (CdtLoc). Toxin production is controlled by regulators specific to each locus. The orphan response regulator, CdtR, encoded within the CdtLoc, up-regulates CDT production. Until now there has been no suggestion that CdtR influences TcdA and TcdB production since it is not carried by all PaLoc-containing strains and CdtLoc is not linked genetically to PaLoc. Here we show that, in addition to CDT, CdtR regulates TcdA and TcdB production but that this effect is strain dependent. Of clinical relevance, CdtR increased the production of TcdA, TcdB and CDT in two epidemic ribotype 027 human strains, modulating their virulence in a mouse infection model. Strains traditionally from animal lineages, notably ribotype 078 strains, are increasingly being isolated from humans and their genetic and phenotypic analysis is critical for future studies on this important pathogen. Here we show that CdtR-mediated toxin regulation did not occur in other strain backgrounds, including a ribotype 078 animal strain. The finding that toxin gene regulation is strain dependent highlights the regulatory diversity between C. difficile isolates and the importance of studying virulence regulation in diverse lineages and clinically relevant strains. Our work provides the first evidence that TcdA, TcdB and CDT production is linked by a common regulatory mechanism and that CdtR may act as a global regulator of virulence in epidemic 027 strains.
authors.affiliation: Infection and Immunity Program, Biomedicine Discovery Institute and Department of Microbiology, Monash University, Clayton, Victoria, Australia.
authors.forename: Shelley A
authors.initials: SA
authors.lastname: Lyon
authors.affiliation: Infection and Immunity Program, Biomedicine Discovery Institute and Department of Microbiology, Monash University, Clayton, Victoria, Australia.
authors.forename: Melanie L
authors.initials: ML
authors.lastname: Hutton
authors.affiliation: Infection and Immunity Program, Biomedicine Discovery Institute and Department of Microbiology, Monash University, Clayton, Victoria, Australia.
authors.forename: Julian I
authors.initials: JI
authors.lastname: Rood
authors.affiliation: Infection and Immunity Program, Biomedicine Discovery Institute and Department of Microbiology, Monash University, Clayton, Victoria, Australia.
authors.forename: Jackie K
authors.initials: JK
authors.lastname: Cheung
authors.affiliation: Infection and Immunity Program, Biomedicine Discovery Institute and Department of Microbiology, Monash University, Clayton, Victoria, Australia.
authors.forename: Dena
authors.initials: D
authors.lastname: Lyras
mesh_terms: D036002:ADP Ribose Transferases / Q000096:biosynthesis; D000818:Animals; D001426:Bacterial Proteins / Q000096:biosynthesis; D001427:Bacterial Toxins / Q000096:biosynthesis; D015153:Blotting, Western; D016360:Clostridioides difficile / Q000378:metabolism*; D004195:Disease Models, Animal; D004761:Enterocolitis, Pseudomembranous / Q000378:metabolism*; D004768:Enterotoxins / Q000096:biosynthesis; D015964:Gene Expression Regulation, Bacterial / Q000502:physiology*; D008297:Male; D051379:Mice; D008810:Mice, Inbred C57BL; D016133:Polymerase Chain Reaction; D014774:Virulence / Q000502:physiology*; D037521:Virulence Factors / Q000096:biosynthesis*
chemical_list: D001426:Bacterial Proteins; D001427:Bacterial Toxins; D004768:Enterotoxins; D037521:Virulence Factors; C041348:tcdA protein, Clostridium difficile; C031815:toxB protein, Clostridium difficile; D036002:ADP Ribose Transferases; C410164:actin-specific ADP-ribosyltransferase, Clostridium