Molecular characterization and evaluation of Clostridium difficile field isolates recovered from pigs with neonatal diarrhea

摘要

During the past decade, Clostridium difficile has become a major cause of neonatal enteritis in pigs and a big economic threat to pig producers.C difficile is a Gram-positive to Gram-variable, spore-forming, anaerobic bacterium, and is a common inhabitant in soil, water, and the intestinal tract of various animals. It has been reported that C difficile can cause enteritis in pigs from newborn to two weeks of age. The affected pigs have mildly distended abdomen, diarrhea, ascites, hydrothorax, and edema of the ascending mesocolon. It is also known that numerous strains of C difficile exist and differ in pathogenicity. The virulence factors include pilus expression, mucosa adherence, capsule production, and the ability to produce toxins. Non-toxigenicC difficile strains are avirulent, while toxigenic strains are virulent and may produce toxin A (TcdA, an enterotoxin) and/or toxin B (TcdB, a cytotoxin). Toxin A and toxin B are encoded by toxin genes tcdA and tcdB respectively. Both toxin A and toxinB are known to be the primary virulence factors of C difficile. Toxin A can cause fluid accumulation in the intestine, while toxin B is extremely cytopathic for tissue culture cells. Other potential virulence factors of the C difficile have also been identified such as a binary toxin called CDT (actin-specific ADP-ribosyltrasferase toxin). The CDT belongs to the group of clostridial binary toxins and is composed of two independent unlinked protein chains, CDTa (enzyme component), and CDTb (binding component). The CDTa and CDTb are encoded by cdtA and cdtB genes respectively. The CDTb recognizes a cell surface receptor and allows the internalization of the CDTa into cytosol. Then the CDTa catalyzes the ADP-ribosylation reaction of monomeric actin and induces a disorganization of the host cell's cytoskeleton.