Final answer:
The exoenzyme that activates prothrombin in blood plasma, facilitating the formation of a fibrin clot for a pathogen to avoid phagocytosis, is coagulase. This strategy is commonly seen in bacteria such as Staphylococcus aureus, which can use clots as a means of escaping the immune system.
Step-by-step explanation:
The exoenzyme that activates prothrombin in blood plasma is coagulase. Prothrombin then combines with fibrinogen, forming a fibrin clot that can be used by a pathogen to hide within, thereby preventing phagocytosis. This mechanism is often employed by certain strains of bacteria, such as Staphylococcus aureus, to avoid being attacked by the immune system. During coagulation, both the intrinsic and extrinsic pathways lead to the common pathway. Here, fibrinogen is converted to fibrin, which is essential in clot formation. Coagulase specifically triggers the conversion of fibrinogen to fibrin without the presence of vessel damage, aiding pathogens in immune system evasion.