Internal Medicine_Infectious Diseases_3

Question 1

What type of bacteria is Streptococcus pyogenes?

Answer 1

It is a gram-positive coccus that forms chains or pairs.

Question 2

What is the main virulence factor of Streptococcus pyogenes that helps evade the immune system?

Answer 2

A hyaluronic acid capsule.

Question 3

What type of hemolysis does Streptococcus pyogenes demonstrate on blood agar?

Answer 3

Beta-hemolysis, creating clear zones around colonies.

Question 4

How can Streptococcus pyogenes be differentiated from other streptococci?

Answer 4

It is bacitracin-sensitive and PYR-positive.

Streptococcus agalactiae is bacitracin resistant and PYR-negative.

Question 5

What are some pyogenic infections caused by Streptococcus pyogenes?

Answer 5

Impetigo: Honey-crusted skin lesions.
Pharyngitis (strep throat): Erythematous and inflamed throat.
Cellulitis and erysipelas: Skin infections with erythema.

Question 6

What toxins does Streptococcus pyogenes produce, and what conditions do they cause?

Answer 6

Pyrogenic exotoxins (SPE): Cause scarlet fever and toxic shock syndrome (TSS).
SpeB: Causes necrotizing fasciitis (flesh-eating bacteria).

Question 7

What are the hallmark symptoms of scarlet fever?

Answer 7

Acute period:
* Fever after a 2 to 5 incubation period.
(including malaise, headache, chills and myalgia)

• Strawberry tongue.
• Pharyngitis with tonsillar exudates
  (enlarged cervical lymph nodes)

Exanthem Phase
* Desquamative “sandpaper” rash 12-48 hours after fever onset
(non-blanching maculopapular rash)

• Rash normally is sparing of the palms and soles but can appear a week later.

Question 8

What is toxic shock syndrome (TSS) caused by Streptococcus pyogenes?

Answer 8

A superantigen-mediated condition characterized by high fever, rash, and shock.

Question 9

What are two major post-infectious complications of Streptococcus pyogenes?

Answer 9

Rheumatic fever.
Post-streptococcal glomerulonephritis (PSGN).

Question 10

Rheumatic fever is a type ____ hypersensitivity reaction

Answer 10

II

Question 11

What is the pathogenesis of rheumatic fever?

Answer 11

Cross-reactivity between M protein and human tissues, leading to molecular mimicry. It confers resistance to phagocytosis and plays a role in the pathogenesis of the immunologic sequela that lead to rheumatic heart disease and glomerulonephritis. Protein M shares a sequence homology with human cardiac myosin.

Streptolysin O lyses red blood cells and immune cells, aiding in immune evasion.

Streptokinase do converts plasminogen to plasmin, facilitating fibrin degradation and tissue invasion.

DNases produced by Streptococcus pyogenes degrade host DNA, helping the bacteria evade immune defenses.

Question 12

What are the JONES criteria for diagnosing acute rheumatic fever?

Answer 12

2 Major or 1 Major with 2 Minor

Major:
J: Joints (migratory polyarthritis).
♡: Carditis (pancarditis).
N: Nodules (subcutaneous).
E: Erythema marginatum (ring-shaped rash).
S: Sydenham chorea (involuntary movements).

Minor:
Fever, Elevated ESR, Polyarthalgias, Prolonged PR interval

Question 13

When does the sequella of Group A Streptococcus tend to show clinical signs after an acute infection?

Answer 13

2 to 4 weeks

Acute rheumatic fever (ARF) is a noninfectious complication of S. pyogenes infection (e.g., tonsillopharyngitis) and can manifest with fever, skin lesions, and elevated ESR. However, the symptoms of ARF typically develop 2–4 weeks after S. pyogenes infection and the skin lesions seen in ARF are subcutaneous nodules and erythema marginatum.

Question 14

What is the long term sequella of rheumatic fever?

Answer 14

Mitral value disease (mitral regurgitation and stenosis)

Question 15

What is the management for rheumatic fever?

Answer 15

ECHO, EKG, Antibiotics, and NSAIDs for joint pain.

Question 16

What antibiotic is preferred for rheumatic fever and how is this managed?

Answer 16

Prophylaxis
Penicillin G IM for 4 weeks, Penicillin V PO daily, or Azithromycin PO daily

With carditis and valve disease until 40 years old or for 10 years
With just carditis until 21 years old or for 10 years
Without carditis until 21 years old or for 5 years

Question 17

What are the hallmark features of Post-streptococcal glomerulonephritis (PSGN)?

Answer 17

Nephritic syndrome

Hematuria (cola-colored urine; dysmorphic RBCs in urine; RBC casts).
Edema and face puffiness (proteinuria < 3.5 g/day).
Hypertension.
Azotemia.

Question 18

When do features of Post-streptococcal glomerulonephritis (PSGN) present following acute infection with Group A streptococcus?

Answer 18

2 weeks following skin or respiratory tract infection.

Question 19

What are the common lab findings for Post-streptococcal glomerulonephritis (PSGN)?

Answer 19

High Antistreptolysin O titer, Low Complement titer, or High DNase B titer

Enlarged Glomeruli and hypercellular growth on light microscope.
Granular appearance on immunofluorescence.
Subepithelial humps of IgG and C3 on electron microscope.

Question 20

Does early antibiotic treatment reduce the risk of PSGN?

Answer 20

No, but it significantly reduces the risk of rheumatic fever.

Question 21

Does streptococcus pyogenes cause meningitis?

Answer 21

No.

The most common syndromes that Streptococcus pyogenes causes are pyogenic infections, Toxic Shock, Scarlet fever, Rheumatic fever, and necrotizing fasciitis.