Question

In general, which bacteria is more virulent, beta-hemolytic or alpha-hemolytic? What additional factors influence bacterial virulence? Please give an example of each hemolysis.

Answer 1

1. which bacteria is more virulent

The severity of a disease is known as virulence. The bacteria which cause more severe effect on a host, is said to be more virulent. Hemolysis is rupturing of RBC. Different reasons are behind the hemolysis.

In Lab this hemolytic property is used to classify some micro organisms. Species of Streptococcus are classified based on their hemolytic properties. They are alpha hemolytic, beta hemolytic and gamma hemolytic.

Beta hemolytic bacteria is more virulent than alpha hemolytic, because alpha-hemolytic species cause oxidization of iron in hemoglobin molecules within red blood cells, giving it a greenish color on blood agar (Used in Lab). Only partial decomposition of hemoglobin happens here. But beta hemolysis cause complete rupture of RBC. So beta is more virulent.

2. Additional factors influence bacterial virulence

The factors that influence interactions between bacteria and target cells(Host) will influence its virulence. Major factors includes,

processes such as

• Adherence to cell membranes
• Colonization and invasion of skin
• Endocytosis and/or phagocytosis (Entry in to the cell)
• Growth, replication, and other metabolic processes
• Local, regional, and systemic spread
• Efficient exit from the infected host (How much they are able to transmit the disease from person to person) or ability of transmission.

These are the direct factors which influence the virulence of a bacteria. Besides this, indirect factors also have a role in it. they are

• Physical and environmental stressors, such as weather, access to food and water.
• Housing conditions (ventilation, humidity, or overcrowding).

3. Example of each hemolysis

Alpha hemolysis is caused by hydrogen peroxide produced by the bacterium, oxidizing hemoglobin producing the green oxidized derivative methemoglobin.  Group of oral streptococci displays alpha hemolysis.

Streptolysin, is the enzyme produced by the bacteria which causes the complete lysis of red blood cells. it is an exotoxin produced by streptococcus species bacteria.Streptolysin O is an oxygen-sensitive cytotoxin, secreted by Streptococcus species and interacts with cholesterol in the membrane RBC and usually results in β-hemolysis.