Microorganisms are used to prepare a widening range of bioactive molecules and enzymes. For example, Streptokinase produced by the bacterium Streptococcus and modified by genetic engineering is used to remove clots from the blood vessels of patients who have suffered a heart attack. Cyclosporin A is an immunosuppressive agent in organ transplantation, while statins produced by the yeast Monascus purpureus serve as blood cholesterol lowering agents, competitively inhibiting the enzyme that synthesizes cholesterol.[13]