Counts on viable Bacteroides fragilis: a modification of the microdroplet technique.

A modification of Sharpe's microdroplet counting technique is presented which permits viable counting of Bacteroides fragilis. Lysed horse blood was added to 0.1 soy digest agar droplets and 2% was found to be the optimal concentration which combined adequate intradroplet colony size with acceptable visibility on the counting screen of the Colworth Droplette machine.