Clostridium difficile

It is the causative agent of pseudomembranous colitis associated with the use of broad spectrum antibiotics. C.difficile is the leading cause of hospital-acquired diarrhea.

Morphology

It is Gram positive bacilli with oval and terminal spores.

Classification

Not relevant.

Human Pathology

It is normally present in 3% of the general population. Hospitalization increases the risk of colonization. When an antibiotic like clindamycin, second and third generation cephalosporins, ampicillin etc. are taken , they kill colonic flora allowing Cl.difficile to grow in large numbers and produce toxins. These exotoxins, TcdA and TcdB, cause disease manifestations.

Once the toxin binds to its receptor on the cell surface, it is internalised by endocytosis. Once released in the cytosol, they glycosylate G proteins called Rho GTPases (Ras superfamily) and inactivate them, thus interfering with intracellular signalling mechanisms. This causes cytopathic and cytotoxic effects. Cytopathic effects include shrinking and rounding of cells, disruption of the actin cytoskeleton and of the tight and adherens junctions, loss of cell-cell contacts, increased epithelial permeability, apoptosis and diarrhea. Cytotoxic effects cause colitis and inflammation.

Clinically it manifests as diarrhea with yellow white looking pseudomembranes. Toxic megacolon and systemic complications can occur in severe cases.

Laboratory diagnosis of Cl.difficile infections

Detection of toxins in stool samples by ELISA is faster. Demonstration of toxin effects by its action on cell culture of Hep-2 or Human Diploid Cells showing characteristic effects is confirmatory.