Mechanism and Diagnosis of Clostridium Difficile Infection

Clostridium difficile is a gram-positive, anaerobic bacillus. It is an important intestinal pathogen that can cause severe diarrhoea and even death in humans. Studies have shown that this pathogen is highly contagious, can produce spores, and can be transmitted by the oral-fecal route. Studies have shown that intestinal dysbiosis caused by long-term antibiotic treatment is an important factor in promoting the occurrence of Clostridium difficile infection in the host. Clostridium difficile pathogens are widely distributed in the natural environment. Sources of infection include asymptomatic carriers, infected hosts, contaminated environments and animal intestines (dogs, cats, livestock, poultry). Among these, animals are important hosts for Clostridium difficile to cause human infection. Studies have found highly virulent strains of Clostridium difficile in farms and slaughterhouses.

Figure 1. Intoxication mechanism of TcdA and TcdB. (Sources: Kordus SL, et al. 2022)

Pathogenesis

• Microbiological Characteristics

Clostridium difficile was first discovered in 1935, but it was not until 1978 that it was confirmed to be associated with diseases such as antibiotic-associated diarrhea and pseudomembranous colitis. Clostridium difficile is a Gram-positive anaerobic spore bacterium with a circular chromosome of approximately 4.3 Mb. Clostridium difficile is divided into toxigenic and non-toxigenic strains that can colonize the large intestine of humans and mammals. Clostridium difficile produces two toxins, namely enterotoxin A (TcdA) and cytotoxin B (TcdB). The former is enterotoxic, causing massive water loss and hemorrhagic necrosis in the intestine. The latter is a potent cytotoxin that can depolymerize actin, damage the cytoskeleton, cause local intestinal wall cell necrosis, and directly damage the intestinal wall. They share an amino-terminal enzymatic domain and a carboxyl-terminal domain. To date, all toxigenic strains contain TcdB, with or without the presence of TcdA. TcdA and Tcd B share a common molecular mechanism of action: inactivation of RhoGTPases by enzymatic glucosylation of conserved threonine residues. This pathway leads to actin depolymerization and cell death and stimulates an inflammatory cascade that exacerbates tissue damage, diarrhea, and pseudomembranous colitis. In addition to these toxins, highly virulent C. difficile strains are known to produce binary toxins (CdtA and CdtB) that have been shown to enhance the virulence of C. difficile through irreversible adenosine diphosphate-ribosylation of actin, inducing the formation of long host cell microtubule protrusions that facilitate bacterial attachment.

• Unique Infection Form-Spores

C. difficile is an obligate anaerobe that cannot survive in an aerobic environment outside the host. The bacterium has two states, a fastidious vegetative cell form that reproduces in the gastrointestinal tract and a hardy spore present in feces that can survive for a long time outside the host. When C. difficile cells encounter certain environmental stimuli (e.g., nutrient deprivation, quorum sensing, and other unidentified stressors), they will initiate the spore formation pathway to produce enough dormant spores to survive in extreme conditions, and spores are the main morphological form for infection and disease transmission. Spore formation and its subsequent germination play a key role in the progression of C. difficile infection (CDI). Under favorable conditions, C. difficile spores germinate and grow to produce pathogenic vegetative forms. These spores are responsible for the persistence and recurrence of C. difficile in the host during CDI. The pathogenesis of C. difficile depends on the formation of aerotolerant dormant spores, which allows C. difficile to persist in the host and spread through host-to-host and contaminated environmental contact. In the host's gastrointestinal tract, dormant spores must germinate from dormancy to form actively growing vegetative cells that produce toxins with pathogenic effects. Under appropriate conditions, when germination receptors sense the presence of small molecules (germination agents), spore germination will be induced. Because the spore form of C. difficile is metabolically inactive, heat-resistant, oxygen-resistant, and can even exist in ethanol-based disinfectants for a long time, it can only be killed by sodium hypochlorite (bleach). Therefore, the surrounding environment of the infection can be a source of its transmission.

Clostridium difficile Antibody

Clostridium difficile Antigens

Clostridium difficile ELISA