Lecture 7 - Streptococcus (Dr. Bailey) Flashcards
Describe Streptococcus species.
- ) Cocci (spherical)
- ) Non-spore forming
- facultative anaerobes
- GRAM POSITIVE
- catalase negative
- infect humans and animals.
Is Streptococcus gram negative or gram positive?
Gram Positive
How can SC be classified? (3)
- Hemolysis Pattern (alpha, beta, gamma)
- how they lyse RBC
- Lancefield Group (A-U)
- antibody activity
- Species
- which sugars do they ferment?
What are the 3 hemolysis patterns?
Alpha
-partially lyse RBCs
-green discoloration
Beta
-completely lyse RBCs
-clear zone
Gamma
- no lysing of RBCsWhat are some categories of Beta strep?
Group A
Group B
“other”
What are some categories of Alpha-Gamma strep?
S. pneumoniae
Group D
-Enterococci
-S. bovis
"other"What are some GROUP A (subcategory of Beta) strep diseases?
- acute pharyngitix (strep throat)
- pyoderma (skin/soft tissues)
- Group A strep pneumonia
- necrotizing fasciitis (gangrene) & myositis
- “flesh-eating bacteria”
- Childbed fever
- foodborne outbreaks
What causes strep throat & scarlet fever?
Group A Strep (GAS)
S. pyogenes
What does S. pyogenes do?
this GAS causes
primary condition
strep throat & scarlet fever
-pus-forming
secondary condition
Acute Rheumatic Fever (ARF)
-non-pus formingWhat group is enterococci?
Group D (of the alpha-gamma group)
What does Acute Rheumatic Fever affect?
inflammation of heart and joints
What does ARF follow?
Acute Pharyngitis
infection @ site of pharynx
Can you treat ARF w/ antibiotic?
No. It is caused by a hyper-reactive immune response. The pathogen is gone at this point.
However, treating acute pharyngitis w/ penicillin can prevent ARF.
How many people get ARF after strep throat?
10%
and they have to take prophylactic antibiotics for life b/c it recurrs often once you have it.
What are two conditions that follow a strep infection by S. pyogenes?
- Acute Rheumatic Fever (ARF)
2. Acute Post-Streptococcal Glomerulonephritis (APSGN)
Describe Acute Post-Streptococcal Glomerulonephritis (APSGN)
- inflammation of glomeruli of kidneys
- can’t prevent it w/ penicillin but only caused by a few serotypes of strep
- can follow pharyngitis OR skin infections
- recurrent attacks rare
- leads to renal failure & dialysis if bad
Activities of Group A infections.
- Encounter
- Entry
- Spread
- Mulitply
- Cause Damage
How do GAS “encounter?”
- live on skin & mucous membranes
- common in kids
- person to person transmission
How do GAS “enter?”
-through BROKEN skin
-bind to FIBRONECTIN of epi cells w/ ADHESINS
-lipoteichoic acid (LTA)
-they have PROTEIN F
-high affinity fibronectin binder
they have M PROTEIN
- KERATINOCYTE (outer skin) binders
How do GAS “spread?”
- localized on skin/mucous membranes
- rapid spread on deep infections
- Proteases
- lyse neutrophils, produce pus - hyaluronidase
- helps spread b/t cells - DNases
- Streptokinase
- makes PLASMIN, which breaks down FIBRIN - Streptolysis S and O
- hemolysis - host cell pore formations
- chemotaxins
- Proteases
What does streptokinase do, and what is it?
Streptokinase is a virulence factor of Group A infections. It lyses blood clots by producing PLASMIN, which breaks down FIBIRIN, which is a clotting substance.
What makes plasmin?
Steptokinase
How do GAS survive and “mulitply?”
Avoid phagocytosis
- M protein
- capsule made w/ blood components
- most important
- Hyaluronic Acid Capsule
- mucoid capsule
- C5a Peptidase
- inactivates chemotaxis of phagocytes
what is M Protein
M protein helps prevent phagocytosis of GAS.
dense coating
prevents opsonins from binding
“variable region” can be attacked by antibodies, but it is HIGHLY variable.
What is Hyaluronic Acid Capsule?
Hyaluronic Acid Capsule prevents phagocytosis of GAS
- makes strep slippery so phagocytes can’t adhere
- shedded for epi attachment
- ARF isolates are heavily encapsulated
How do GAS “damage?”
Streptococcal Pyrogenic Exotoxins (SPEs)
What are Streptococcal Pyrogenic Exotoxins(SPEs)?
- cause red rash of scarlet fever
- can directly activate T cells w/out antigen in context of MHC
- inflammatory response in tissues
- SUPERANTIGENS that can mimic the effects of endotoxins (activated T cells release cytokines)
- produce streptococcal toxic shock syndrome
What is a SUPERANTIGEN?
Streptococcal Pyrogenic Exotoxin (SPE) can activate T-cells w/out MHC
Which is more common, group A or Group B strep?
Group B
Which hemolysis classification is Group B strep?
Beta, just like Group A
What does Group B strep commonly cause?
- neonatal sepsis
- meningitis
(common in adults with chronic disease)
How does Group B strep cause problems?
Their POLYSACCHARIDE CAPSULE is antigenic.
this is unlike the hyaluronic capsule of GAS
Where is Group B strep found?
lower GI tract
female genital tracts
What are the Lancefield classifications of the “other” Beta strep? (not GAS or GBS)
C, G, and F
S. zooepidemicus in most common. affects cattle, horses, and humans
What is the hemolytic classification of Group D strep?
Alpha, Gamma
Describe Group D strep
- alpha, gamma hemolytic
- enterococci & nonenterococci (like S. bovis)
- in normal flora of GI and genitourinary tracts
- low virulence
Are enterococci normally virulent?
No, but they are BAD when they are.
What is the “world’s toughest pathogenic bacteria?”
Enterococci
grow in high salt
not killed by penicillin
resistant to most antibiotics
How is enterococci treated?
combo of PENICILLIN (leaky cell wall) & AMINOGLYCOSIDE (limit PRO synthesis)
What is the untreatable type of enterococci?
Vancomycin resistant enterococci (VREs)
can transfer their resistance
What is a nonenterococcal Group D strep?
S. Bovis
- most common for human disease
- subacute bacterial endocarditis- affects abnormal heart valves
Does S. bovis grow in high salt?
No. only enterococci do this. S. bovis is nonenterococcal.
Is S. bovis killed by penicillin?
Yes, but enterococci are not.
What color is Viridans strep associated with?
Green (alpha-hemolytic)
most common cause of subacute bacterial endocaridits
Strep Mutans (“viridan strep)
dental caries
most prevalent forms of infectious disease
S. mutans, sanguis, salivarius, mitis,
