Plate coagulase and fibrinolysin tests for staphylococci.

" Coagulase Plates" When human blood bank plasma is mixed with nutrient agar in a concentration of about 12 to 15O% v v and poured into Petri dishes at a temperature of 45° C. the mixture sets as a clear gel. Staphylococci inoculated on to this medium develop opaque haloes around the colonies in 12 to 48 hours if they produce coagulase (Lack and Wailling, 1954). The advantages of the plate method are that mixtures of coagulase-positive and negative staphylococci may be sorted out on primary culture, and that highly fibrinolytic staphylococci, which may dissolve their coagulase clots in the test-tube during an overnight incubation, ate less likely to be overlooked on the plate. The disadvantages of this method as originally described are that it may take more than 12 hours to detect coagulase, and that some batches of bank plasma are unsuitable by reason of their low fibrinogen content. Human fibrinogen alone is satisfactory, as it is always contaminated by the requisite co-factor, but it is too scarce; commercial bovine fibrinogen is too deficient in co-factor to use alone. But bovine fibrinogen combined with a source of co-factor provides an excellent substrate for the platecoagulase test, and the first section deals with the results of plate tests using different commonly available plasmas or sera to supplement bovine fibrinogen.