What is the source from which streptokinase is isolated?

Streptokinase is an enzyme that is primarily isolated from beta-hemolytic streptococci, particularly from group A Streptococcus. This enzyme plays a crucial role in breaking down blood clots, as it converts plasminogen to plasmin, which then dissolves fibrin clots. The specific bacteria from which streptokinase is derived have been utilized in medical applications, particularly in treating conditions like myocardial infarction and pulmonary embolism. The other options listed, while being significant in their own right, do not serve as sources for streptokinase, which is unique to the beta-hemolytic streptococci.