Lecture 6 - Streptococcus Flashcards
What is cellulitis
Enzymes that degrade tissue that cause bacterial spreading
What is mutualism and where is used in context when talking about the body and normal flora?
Mutualism: both organisms benefit from a relationship
The body and its normal bacterial flora like streptococcus and staphylococcus have a mutualistic relationship
What are the 4 ways to classify Streptococcus
- Hemolysis (alpha, beta or gamma)
- Lancefield (serology)
- Natural clusters
- Divide genus into 6 major groups based on 16s + RNA seq.
This natural cluster is characteristic of oral flora (S. mutans), No C-CHO and many are alpha-hemolytic (green).
Viridans (S. mutans, S. mitis, S. salivarius)
This cluster is characterized as the main pathogen of Streptococcus, contains alpha and beta hemolytic bacteria as well as Group A and B.
Pyogenic (S. aureus, S. agalactiae, S. pneumonia
This cluster is found mostly in the GI and are either alpha or beta hemolytic
Enterococci (E. bovis, E. swiss, etc.)
Is the Lactic natural cluster hemolytic?
No, would be considered gamma hemolytic
What is the oldest way to classify streptococcus
Hemolysis
What is the Lancefield classification system?
Uses serology to classify the strept based on their on their different surface C-Carbohydrates (cell wall polysaccharides)
Classify S. pyogenes based on hemolysis, lancefield and cluster
Beta-hemolytic
Group A
Pyogenic
Classify S. agalactiae based on hemolysis, lancefield and cluster
B-hemolytic
Group B
Pyogenic
When is the lancefield classification most useful?
When classifying the B-hemolytic bacteria
3 characteristics of S. pyogenes
- B-hemolytic, Group A
- Many toxins
- Strept throat, rheumatic fever, Cellulitis
3 characteristics to S. agalactiae
- B-hemolytic, Group B
- Capsule
- Neonatal sepsis
3 characteristics of S. pneumiae
- alpha-hemolytic
- Capsule
- Pneumonia, ear infections
2 characteristics of ‘Viridans’ Strept
- alpha - hemolytic
2. Endocarditis, caries
Which two ways can Strep camouflage itself from immune system?
- Camouflage with host plasma protein - fibrinogen - to ‘hide’ from the immune system.
- Producing a hyaluronic acid capsule similar to that found in host extracellular matrix
How does a bacteria attach itself to host cell to evade immune system
Facilitates colonization by using bacterial cell components such as M protein and F protein that cross-link pili to host epithelial cells
How can repeated strept throat occur?
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
What is another name for cytolytic toxins and what do they do?
Streptolysins, they kill leukocytes and destroy clots respectively. This stops the immune system from preventing the spread of the disease
What are the two ways that Strep can reduce complement
- Produce a C5a peptidase that inactivates this 911 molecule and thus interferes with immune signaling
- Coating the tips of their M protein pili with host factor H, which destabalizes C3b which prevents complement and immune signaling
What are the 3 main forms of disease for S. pyogenes
- Pyogenic infection = local growth
- Toxic systemic disease
- Immune Sequelae Disease
5 examples of pyogenic infection for Strep. pyogenes
- Strept throat (5-30% carriers, 100 different M-protein strains)
- Puerperal Fever
- Pneumonia
- Skin infection
- Vascular Disease
This skin infection due to a local pyogenic infection from S. pyogenes is common in children
Impetago
Two examples of Toxic Systemic Disease
- Scarlet Fever
2. Toxic Shock-like syndrome
Describe a toxic systemic disease
Spread throughout the body not by the bacteria but by their exotoxins
2 major examples of Immune Sequelae diseases
- Rheumatoid Fever
2. Glomerulonephritis
What type of hypersensitivity is Rheumatoid factor and Glomerulonephritis
Rheumatoid factor - Hypersensitivity II
Glomerulonephritis - Hypersensitivity III
What two diseases related to Streptococcus can be attributed to Superantigens
Scarlet Fever
Streptococcal Toxic Stress-like syndrome (STSS)
What is Type II Hypersensitivity
When an antibody binds to an epitope on the host tissue being damaged.
Explain Rheumatic fever
When an antibody made for S. pyogenes cross-reacts with heart tissue epitopes and damages the heart.
What is Type III Hypersensitivity
The result of immune-complex-induced innocent bystander tissue damage
What is an Arthus reaction
A Type III hypersensitivty that occurs in tissue spaces
What is the key to Type III Hypersensitivity
The tissue is not being damaged directly by an antibody. The tissue is an innocent bystander!
What three ways can Strep cause damage to the heart
- Major pathogens get into blood from pharyngitis, pneumonia, a wound, etc. may land on heart tissue and cause an acute bacterial endocarditis
- Immune response to S. pyogenes cross react and damage heart tissue
- Patients with past heart damage are at a greater risk for sub-acute bacterial endocarditis
What is antibiotic prophylaxis
sometimes used to pre-treat, prior to invasive oral procedures, patients who have damaged hearts
How is Amoxicillin dangerous to individuals with previous heart damage
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
