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Lecture

Microbiology and Immunology 2500A/B Lecture Notes - Toxic Shock Syndrome, Streptococcal Pharyngitis, Neutrophil Extracellular Traps


Department
Microbiology and Immunology
Course Code
MICROIMM 2500A/B
Professor
C.Y.Kang

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Streptococci Feb. 27, 2013
- It is a gram-positive; coccus shaped & aerotolerant anaerobes that grow in chains
- Oxygen is not used by Streptococci (anaerobic), but it does not kill them (they are
tolerant to it, unlike Clostridia which are strict anaerobes)
- The word “Streptos” is a Greek word for bent or twisted the bent or twisted shape can
be seen on the gram strain
- They are non-motile & non-endospore forming
- They are initially classified by their pattern of hemolysis on blood agar
α-hemolytic
They can cause partial hemolysis: erupt cells partially
S. pneumoniae pneumococcus
S. viridans endocarditis: infection of heart valves
S. mutans tooth decay
S. thermaphilus (not a pathogen) Daily foods
Not all Strep are pathogenic
β-hemolytic
S. pryogenes (Group A Strep)
S. agalactiae (Group B Strep)
S. equi (Group C Strep); it causes infection in horses
γ-hemolytic
Enterococcus species (Group D Streptococcus)
Lactococcus (Group N Streptococcus) not a pathogen
Streptococcus pyogenes: Pathogen
It is a common human specific pathogen; humans are the only reservoir for this
pathogen; an extracellular pathogen inside the cells but generally outside the host
cells
“Pyo” means pus this occurs to inflammation, neutrophils leading to pus
In 5-15% cases there is asymptomatic carriage; in this situation, the patient is a carrier of
the disease or infection, however, they do not experience any symptoms
Lancefield Classification
These are classified on the
basis of surface
carbohydrates antigens

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It was a major cause of mortality from scarlet fever, puerperal sepsis & wound
infections in soldiers
In the modern day, this pathogen causes pharyngitis & impetigo; it also causes severe
invasive streptococcal disease and the streptococcal toxic shock syndrome (Flesh eating
disease)
It is an important cause of “post infection sequelae” including acute rheumatic fever;
something happens after the infection, infections goes away and then it develops the
disease
It is capable of producing an arsenal of key virulence factors
Master of hiding from the immune system and capable to causing severe damage
M Protein
- An anti-phagocytic cell surface expressed protein
- Binds “Factor H” (host protein) of the complement system
- Factor H is a complement regulatory protein that protects self-cells from C3b deposition
Strep binds to Factor H so that the complement system is unable to detect it
because it is being protected by Factor H
- Greater than 100 M protein serotypes
- Hypervariable N-terminus Basis for M protein serotypes (antigenically distinct)
Different M protein serotypes will cause different disease (Linkage of specific M
protein to a specific disease)
Ex. M1, M3 typically cause pharyngitis & invasive disease
Ex. M18 typically cause acute rheumatic fever
- However, if you have antibodies to a particular M protein serotype, you will opsonize
and kill these bacteria
- S. pyogenes makes 2 hemolysins (they target red blood cells as well as other cells; ex.
leukocytes)
Streptolysins (O & S)
Streptolysin S produced β-hemolysis
Streptolysin O is Oxygen sensitive and can be seen under anaerobic
conditions
Hyaluronic acid capsule
A polysaccharide (sugar capsule)
Hyaluronic acid is a major component of host tissues bacteria “look like
self”
This is why we are unable to make the capsule vaccine because then it would
target our healthy cells
Can also block opsonization through C3b (typical of other capsules)
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