What is the primary purpose of Blood Agar (BA)?

Blood agar serves as a differential medium specifically designed to identify and differentiate bacterial species based on their ability to lyse red blood cells, which is evident through distinct hemolysis patterns. This medium contains intact red blood cells providing the necessary nutrients for growth and allows the observation of hemolytic activity.

When bacteria are cultured on blood agar, they may exhibit three primary types of hemolysis: beta-hemolysis (complete lysis of red blood cells leading to a clear zone around the colony), alpha-hemolysis (partial lysis resulting in a greenish discoloration on the agar), and gamma-hemolysis (no lysis, showing no change in the medium). This characteristic is critical for differentiating various bacterial species, particularly Streptococcus species, and aids in diagnosing infections.

In contrast, options that suggest the main purpose is to isolate Gram-positive bacteria or to inhibit bacterial growth do not accurately reflect the primary function of blood agar. Also, while blood agar can support the growth of some anaerobic bacteria under certain conditions, its main role is not primarily focused on promoting anaerobic growth. Therefore, the correct answer highlights the essential function of blood agar in differentiating bacteria based on their hemolytic capabilities.