Microbiology Practice Exam

Which type of hemolysis indicates partial breakdown of red blood cells?

1. Alpha hemolysis

2. Beta hemolysis

3. Gamma hemolysis

4. Delta hemolysis

The correct answer is: Alpha hemolysis

Alpha hemolysis refers to the partial breakdown of red blood cells in the presence of certain bacteria, particularly those in the Streptococcus genus. This process results in a greenish discoloration surrounding colonies on blood agar, due to the conversion of hemoglobin to methemoglobin or other reduced forms of hemoglobin. The partial degradation indicates that the bacteria possess certain enzymes (hemolysins) that can lyse red blood cells, but not completely; thus, the residual intact cells and heme products lead to the characteristic green hue. In contrast, beta hemolysis indicates complete lysis of red blood cells, resulting in clear zones around bacterial colonies, while gamma hemolysis (or non-hemolytic) indicates no lysis and therefore shows no changes in the medium. Delta hemolysis is not a standard term used in describing hemolytic patterns in microbiology. This distinction is important in clinical microbiology for identifying and categorizing bacterial species based on their hemolytic properties.