Activation of coagulase clotting by trypsin inhibitor

Comparison of animal sera for suitability in coagulase testing

The sera of several animals were examined for suitability in coagulase testing. The assay for coagulase-reacting factor (CRF) activities of the whole sera indicated the following relative concentrations of CRF: human > pig > rabbit > horse > bovine, chicken, and lamb. Human, pig, and rabbit sera had adequate amounts of CRF for coagulase testing. The plasmin activities of the different sera, arranged from the strongest to the weakest, were as follows: rabbit > human > lamb > horse > bovine, chicken, and pig. Fibrinolysis was observed when rabbit, human, lamb, or horse sera were incorporated into coagulase test agars. Pig serum was superior to the other sera for use in the plate test for coagulase since it had adequate amounts of CRF and the plasminogen-plasmin system was not activated by staphylokinase or staphylococcal Müller factor. Heparinized pig plasma was more suitable than citrated pig plasma since citrate interfered with the growth of Staphylococcus aureus, and the use of heparinized plasma prevented false-positive coagulase reactions due to citrate utilization.

Polymyxin-coagulase-mannitol-agar. I. A selective isolation medium for coagulase-positive Staphylococci

A selective, differential plating medium was developed for the isolation and identification of coagulase-positive and mannitol-fermenting staphylococci. Coagulase produced by growing Staphylococcus aureus caused an opaque zone of fibrin to form around each colony. Several strains of S. aureus produced a visible coagulase reaction by 8 hr, and all strains gave a positive reaction before 12 hr. Mannitol fermentation was usually observed between 12 and 36 hr. Rabbit serum was filtered through Sephadex G-100 to obtain plasmin- and plasminogen-free coagulase-reacting factor (CRF). False-negative reactions, caused by staphylokinase and staphylococcal Müller factor action on plasminogen, were eliminated when this CRF was used. False-positive reactions by lipolytic, coagulase-negative staphylococci were reduced, since gel filtration removed the serum lipoprotein which served as a primary source of opacity. The addition of 75 mug of polymyxin B per ml selectively retarded the growth of S. epidermidis and minimized false-positive reactions caused by citrate-utilizing gram-negative rods. The preparation, characteristics, and use of the medium are presented.