Question

3. Staphylococcus aureus is associated with many phages that are both lytic and lysogenic. What is the difference between a lytic phage and a lysogenic phage?

4.Describe the genus Streptococcus, where it is found in/on the human body, and how it isclassified.

5. What is one of the most common clinical manifestations associated with Streptococcus pyogenes? What are 3 other types of diseases associated with Streptococcus pyogenes .

Answer 1

Solution 3).Difference between the lytic cycle and the lysogenic cycle is that lysogenic cycle does not lyse the host cell straight away whereas the lytic cycle lyse the host cell. Phages that replicate only through lytic cycle are known as virulent phages while phages that replicate using both lytic and lysogenic cycles are known as temperate phages.Temperate phages usually do not kill the host bacterial cells they infect. Their chromosome gets integrated into the host cell chromosome. Such phage DNA is called prophage and the host bacteria are said to be lysogenized.

Solution 4).Species of Streptococcus are classified based on their hemolytic properties which are as follows:

• Alpha-hemolytic species:oxidises iron in hemoglobin molecules within red blood cells, giving it a greenish color on blood agar.
• Beta-hemolytic species:cause complete rupture of red blood cells. On blood agar, this appears as wide areas clear of blood cells surrounding bacterial colonies.
• Gamma-hemolytic species:cause no hemolysis.

Solution 5).Streptococcus pyogenes basically colonises the throat, genital mucosa, rectum, and skin.The most common clinical manifestations associated with Streptococcus pyogenes are streptococcal pharyngitis(strep throat),streptococcal toxic shock syndrome (STSS), necrotizing fasciitis (NF), pneumonia, and bacteremia. Other diseases caused by Streptococcus pyogenes are rheumatic fever, rheumatic heart disease, scarlet fever, localized skin infection (impetigo).Also causes Erysipelas and cellulitis which are characterized by multiplication and lateral spread of Streptococcus pyogenes in deep layers of the skin.