The VirS/VirR Two-Component System Regulates the Anaerobic Cytotoxicity, Intestinal Pathogenicity, and Enterotoxemic Lethality of Clostridium perfringens Type C Isolate CN3685
Authors: Ma Menglin , Vidal Jorge , Saputo Juliann , McClane Bruce A. , Uzal Francisco 
Published: January 2011

Clostridium perfringens
vegetative cells cause both histotoxic infections (e.g., gas gangrene) and diseases originating in the intestines (e.g., hemorrhagic necrotizing enteritis or lethal enterotoxemia). Despite their medical and veterinary importance, the molecular pathogenicity of
C. perfringens
vegetative cells causing diseases of intestinal origin remains poorly understood. However,
C. perfringens
beta toxin (CPB) was recently shown to be important when vegetative cells of
C. perfringens
type C strain CN3685 induce hemorrhagic necrotizing enteritis and lethal enterotoxemia. Additionally, the VirS/VirR two-component regulatory system was found to control CPB production by CN3685 vegetative cells during aerobic infection of cultured enterocyte-like Caco-2 cells. Using an isogenic
virR
null mutant, the current study now reports that the VirS/VirR system also regulates CN3685 cytotoxicity during infection of Caco-2 cells under anaerobic conditions, as found in the intestines. More importantly, the
virR
mutant lost the ability to cause hemorrhagic necrotic enteritis in rabbit small intestinal loops. Western blot analyses demonstrated that the VirS/VirR system mediates necrotizing enteritis, at least in part, by controlling
in vivo
CPB production. In addition, vegetative cells of the isogenic
virR
null mutant were, relative to wild-type vegetative cells, strongly attenuated in their lethality in a mouse enterotoxemia model. Collectively, these results identify the first regulator of
in vivo
pathogenicity for
C. perfringens
vegetative cells causing disease originating in the complex intestinal environment. Since VirS/VirR also mediates histotoxic infections, this two-component regulatory system now assumes a global role in regulating a spectrum of infections caused by
C. perfringens
vegetative cells.

IMPORTANCE
Clostridium perfringens
is an important human and veterinary pathogen.
C. perfringens
vegetative cells cause both histotoxic infections, e.g., traumatic gas gangrene, and infections originating when this bacterium grows in the intestines. The VirS/VirR two-component regulatory system has been shown to control the pathogenicity of
C. perfringens
type A strains in a mouse gas gangrene model, but there is no understanding of pathogenicity regulation when
C. perfringens
vegetative cells cause disease originating in the complex intestinal environment. The current study establishes that VirS/VirR controls vegetative cell pathogenicity when
C. perfringens
type C isolates cause hemorrhagic necrotic enteritis and lethal enterotoxemia (i.e., toxin absorption from the intestines into the circulation, allowing targeting of internal organs). This effect involves VirS/VirR-mediated regulation of beta toxin production
in vivo
. Therefore, VirS/VirR is the first identified global
in vivo
regulator controlling the ability of
C. perfringens
vegetative cells to cause gas gangrene and, at least some, intestinal infections.