Streptococcus

Question 1

Streptcoccus Structure

Answer 1

• Gm positive cocci that are catalase negative.
• Major virulence factor is capsule
• Can cause a host of diseases
• Can be classified based on type of hemolysis, alpha is green on blood agar, beta is clear, and gamma is no hemolysis

Question 2

Major Clinical Species

Answer 2

• Strep Pneumo, Strep Viridans, Strep Pyogenes (Group A Strep), Strep Agalactiae (Group B strep), Strep Bovis (gamma hemolysis)
• Also enterobactae faecalis

Question 3

Strep Pneumoniae

Answer 3

• Alpha hemolytic strep, capsule is major virulence factor, optichin sensitive (different from viridans), also can use quelling reaction of Ab binding to capsule
• Can cause a host of diseases from skin infections to meningitis and bacteremia
• pneumovax vaccine for prevention of meningitis in young adults

Question 4

Strep Viridans

Answer 4

• Alpha hemolysis, optichin insensitive

- a number of organisms fall in this group including strep mutans which causes dental carries.

Question 5

Strep Pyogenes (group A strep)

Answer 5

• Beta hemolytic, bacitracin sensitive and bile soluble.
• Cause a host of infections from pharyngitis to skin infections and meningitis
• Has SPE superantigen toxin that can cause toxic shock syndrome
• Can cause non supperative sequalae including post streptococcal glomerulonephritis, Acute rheumatic fever
• Important to determine cause of pharyngitis, because will be treated if it is group A strep

Question 6

Strep Agalactiae (group B strep)

Answer 6

• beta hemolytic, bacatracin insensitive
• Normal flora of 10-30% of women in vagina and rectum, huge risk of passing on to infants
• Cause of infant meningitis and bacteremia, high risk mothers must be treated prophylactically

Question 7

Step Bovis

Answer 7

-Causes baceteremia in patients with occult malignancy of the colon.

Question 8

Enterococus

Answer 8

-Faecalis and other species can cause infections in the immunocompromised host, nosocomial possible source.

Question 9

Other Group A strep Information

Answer 9

• Scarlet fever is when a patient with pharyngitis is infected with a strain that contains and exfoliative toxin and causes a red rash that eventually desquamates.
• Need to treat pharyngitis to prevent non suppurative complications of Ag-Ab cross reactivity
• Impetigo is almost always caused by S Aureus or Group A strep
• Can also cause infection and sepsis in mother after birth
• Major cause of necrotizing fascitis.