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Medical Microbiology > Lecture 6 - Streptococcus > Flashcards

Lecture 6 - Streptococcus Flashcards

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USMLE® Step 1 flashcards Biology 101 flashcards
0
Q

What is cellulitis

A

Enzymes that degrade tissue that cause bacterial spreading

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1
Q

What is mutualism and where is used in context when talking about the body and normal flora?

A

Mutualism: both organisms benefit from a relationship

The body and its normal bacterial flora like streptococcus and staphylococcus have a mutualistic relationship

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2
Q

What are the 4 ways to classify Streptococcus

A
  1. Hemolysis (alpha, beta or gamma)
  2. Lancefield (serology)
  3. Natural clusters
  4. Divide genus into 6 major groups based on 16s + RNA seq.
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3
Q

This natural cluster is characteristic of oral flora (S. mutans), No C-CHO and many are alpha-hemolytic (green).

A

Viridans (S. mutans, S. mitis, S. salivarius)

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4
Q

This cluster is characterized as the main pathogen of Streptococcus, contains alpha and beta hemolytic bacteria as well as Group A and B.

A

Pyogenic (S. aureus, S. agalactiae, S. pneumonia

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5
Q

This cluster is found mostly in the GI and are either alpha or beta hemolytic

A

Enterococci (E. bovis, E. swiss, etc.)

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6
Q

Is the Lactic natural cluster hemolytic?

A

No, would be considered gamma hemolytic

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7
Q

What is the oldest way to classify streptococcus

A

Hemolysis

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8
Q

What is the Lancefield classification system?

A

Uses serology to classify the strept based on their on their different surface C-Carbohydrates (cell wall polysaccharides)

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9
Q

Classify S. pyogenes based on hemolysis, lancefield and cluster

A

Beta-hemolytic
Group A
Pyogenic

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10
Q

Classify S. agalactiae based on hemolysis, lancefield and cluster

A

B-hemolytic
Group B
Pyogenic

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11
Q

When is the lancefield classification most useful?

A

When classifying the B-hemolytic bacteria

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12
Q

3 characteristics of S. pyogenes

A
  1. B-hemolytic, Group A
  2. Many toxins
  3. Strept throat, rheumatic fever, Cellulitis
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13
Q

3 characteristics to S. agalactiae

A
  1. B-hemolytic, Group B
  2. Capsule
  3. Neonatal sepsis
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14
Q

3 characteristics of S. pneumiae

A
  1. alpha-hemolytic
  2. Capsule
  3. Pneumonia, ear infections
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15
Q

2 characteristics of ‘Viridans’ Strept

A
  1. alpha - hemolytic

2. Endocarditis, caries

16
Q

Which two ways can Strep camouflage itself from immune system?

A
  1. Camouflage with host plasma protein - fibrinogen - to ‘hide’ from the immune system.
  2. Producing a hyaluronic acid capsule similar to that found in host extracellular matrix
17
Q

How does a bacteria attach itself to host cell to evade immune system

A

Facilitates colonization by using bacterial cell components such as M protein and F protein that cross-link pili to host epithelial cells

18
Q

How can repeated strept throat occur?

A

Through strain variation to avoid the Ab. There are over 150 different strains of strep each with a different antigenic variant of the M protein

19
Q

What is another name for cytolytic toxins and what do they do?

A

Streptolysins, they kill leukocytes and destroy clots respectively. This stops the immune system from preventing the spread of the disease

20
Q

What are the two ways that Strep can reduce complement

A
  1. Produce a C5a peptidase that inactivates this 911 molecule and thus interferes with immune signaling
  2. Coating the tips of their M protein pili with host factor H, which destabalizes C3b which prevents complement and immune signaling
21
Q

What are the 3 main forms of disease for S. pyogenes

A
  1. Pyogenic infection = local growth
  2. Toxic systemic disease
  3. Immune Sequelae Disease
22
Q

5 examples of pyogenic infection for Strep. pyogenes

A
  1. Strept throat (5-30% carriers, 100 different M-protein strains)
  2. Puerperal Fever
  3. Pneumonia
  4. Skin infection
  5. Vascular Disease
23
Q

This skin infection due to a local pyogenic infection from S. pyogenes is common in children

A

Impetago

24
Q

Two examples of Toxic Systemic Disease

A
  1. Scarlet Fever

2. Toxic Shock-like syndrome

25
Q

Describe a toxic systemic disease

A

Spread throughout the body not by the bacteria but by their exotoxins

26
Q

2 major examples of Immune Sequelae diseases

A
  1. Rheumatoid Fever

2. Glomerulonephritis

27
Q

What type of hypersensitivity is Rheumatoid factor and Glomerulonephritis

A

Rheumatoid factor - Hypersensitivity II

Glomerulonephritis - Hypersensitivity III

28
Q

What two diseases related to Streptococcus can be attributed to Superantigens

A

Scarlet Fever

Streptococcal Toxic Stress-like syndrome (STSS)

29
Q

What is Type II Hypersensitivity

A

When an antibody binds to an epitope on the host tissue being damaged.

30
Q

Explain Rheumatic fever

A

When an antibody made for S. pyogenes cross-reacts with heart tissue epitopes and damages the heart.

31
Q

What is Type III Hypersensitivity

A

The result of immune-complex-induced innocent bystander tissue damage

32
Q

What is an Arthus reaction

A

A Type III hypersensitivty that occurs in tissue spaces

33
Q

What is the key to Type III Hypersensitivity

A

The tissue is not being damaged directly by an antibody. The tissue is an innocent bystander!

34
Q

What three ways can Strep cause damage to the heart

A
  1. Major pathogens get into blood from pharyngitis, pneumonia, a wound, etc. may land on heart tissue and cause an acute bacterial endocarditis
  2. Immune response to S. pyogenes cross react and damage heart tissue
  3. Patients with past heart damage are at a greater risk for sub-acute bacterial endocarditis
35
Q

What is antibiotic prophylaxis

A

sometimes used to pre-treat, prior to invasive oral procedures, patients who have damaged hearts

36
Q

How is Amoxicillin dangerous to individuals with previous heart damage

A

It is the most common used antibody as a prophylaxis. The b-lactam ring that is very reactive makes patients develop hypersensitivity reactions to penicillin. Most serious is Type I hypersensitivity

Medical Microbiology (17 decks)

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