An in-vitro model of colonisation resistance to Clostridium difficile infection.

To investigate the importance of the normal gut flora in preventing the establishment of Clostridium difficile in vivo we have developed an in-vitro test system based on growth in faecal emulsions. Growth of C. difficile and cytotoxin production are inhibited in faecal emulsions from healthy adults, but not in sterilised emulsions; the importance of viable bacteria in the inhibitory system is evident. Generally, faecal emulsions derived from infants, children and geriatric patients were less inhibitory than those from healthy adults. Those from bottle-fed infants were significantly less inhibitory than those from breast-fed infants. Decreased levels of cytotoxin in the latter group were attributed to the acidic pH of the stools. With the different patient groups studied, faecal samples not inhibitory to C. difficile in vitro were obtained from 21% of patients with antibiotic-associated diarrhoea, 33% of those taking antibiotics but who did not have diarrhoea, 18.7% of those with diarrhoea unassociated with antibiotics, and 79% of those with C. difficile-mediated diarrhoea. In some cases inhibition was due to low faecal pH, as in some infants, and in others to other filterable substances. The degree of inhibition could not be linked to specific volatile fatty acids or enzymes.