COAGULASE Production of coagulase is indicative of a pathogenic staphylococcal species (Staphylococcus aureus).Coagulase acts by a thrombinase-like action.In normal blood clotting,the following reactions occur: prothrombin +CaCl prothrombinase thrombin thrombin fibrinogen thrombinase fibrin(clot) Coagulase acts within host tissues to convert fibrinogen to thrombin.It is theorized that the fibrin meshwork that is formed surrounds the bacterial cells or infected tissues,protecting the organism from nonspecific host defense mechanisms such as phagocytosis. A coagulase-positive strain of Staphylococcus will cause fibrin formation, .e.will clot plasma.Clot formation within 4 hours is interpreted as a positive result and indicates a virulent S.aureus strain. HEMOLYSINS Hemolysins are extracellular enzymes that can be detected by their ability to lyse red blood cells.Hemolysins are produced by various pathogenic bacteria and are believed to play a role in the virulence of the organism.The streptococci are classified by their hemolytic activity.Three types of hemolytic reactions can be observed on blood agar plates(nutrient agar supplemented with a 5% concentration of sheep blood).Alpha hemolysins partially lyse the red blood cells and reduce the hemoglobin to methemoglobin which produces a green zone around the colony.Beta hemolysins cause complete lysis of the red blood cells and there is a clearing of the hemoglobin around the colony.The term gamma hemolysis is used to designate no hemolysis or change in the red blood cells. 54 54 COAGULASE Production of coagulase is indicative of a pathogenic staphylococcal species (Staphylococcus aureus). Coagulase acts by a thrombinase-like action. In normal blood clotting, the following reactions occur: prothrombin + CaCl2 prothrombinase > thrombin thrombin + fibrinogen thrombinase > fibrin (clot) Coagulase acts within host tissues to convert fibrinogen to thrombin. It is theorized that the fibrin meshwork that is formed surrounds the bacterial cells or infected tissues, protecting the organism from nonspecific host defense mechanisms such as phagocytosis. A coagulase-positive strain of Staphylococcus will cause fibrin formation, i.e. will clot plasma. Clot formation within 4 hours is interpreted as a positive result and indicates a virulent S. aureus strain. HEMOLYSINS Hemolysins are extracellular enzymes that can be detected by their ability to lyse red blood cells. Hemolysins are produced by various pathogenic bacteria and are believed to play a role in the virulence of the organism. The streptococci are classified by their hemolytic activity. Three types of hemolytic reactions can be observed on blood agar plates (nutrient agar supplemented with a 5% concentration of sheep blood). Alpha hemolysins partially lyse the red blood cells and reduce the hemoglobin to methemoglobin which produces a green zone around the colony. Beta hemolysins cause complete lysis of the red blood cells and there is a clearing of the hemoglobin around the colony. The term gamma hemolysis is used to designate no hemolysis or change in the red blood cells