IDIT 27: MICROBIOLOGY 8-Beta-Hemolytic Streptococci
Terms
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Lancefeild Group A:
Streptococcus Pyogenes-
Metabolism -
1)Catalase -
2)Microaerophilic
3) Beta-hemolytic due to enzymess that destroy red and white blood cells
A. Streptolysin O:
a. Oxygen labile
b. Antigenic
B. Streptolysin-S
a. Oxygen stable
b. Non-antigenic -
Lancefeild Group A:
Streptococcus Pyogenes-
Virulence -
M protein (70 types)
a. Adherence factor
b. Anti-phagocytic
c. Antigenic: induces Ab which can lead to phagocytosis
2. Lipoteichoic Acid: Adherence factor
3. Streptokinase
4. Hyaluuronidase
5. DNAase
6. Ant-C5a peptidase -
Lancefeild Group A:
Streptococcus Pyogenes-
Toxins -
-Erythrogenic or Pyrogenic Toxin (produced only by lysogenized Group A Streptococci): responsible for scarlet fever
3. Toxic Shock Sy - Lancefield groups
- a serologic classification dividing hemolytic streptococci into groups (A to O) which bear a definite relationship to their sources, based upon precipitation tests depending upon group-specific substances that are carbohydrate in nature; e.g., Group A contains strains most pathogenic for humans; B, strains from mastitis in cows and from normal milk, including strains from the human throat and vagina; C, strains from various lower animals, including a number from cattle and the human throat; D, strains from cheese and humans; E, strains from certified milk; F, strains mainly from the human throat, associated with tonsillitis; G, strains from humans, a few from monkeys and dogs; and H, K, and O, nonpathogenic strains occasionally from normal human respiratory tracts.
- streptolysin
- A hemolysin produced by streptococci.
- streptokinase
- An extracellular metalloenzyme from hemolytic streptococci that cleaves plasminogen, producing plasmin, which causes the liquefaction of fibrin (
- streptodornase ( also called DNAase B)
- extracellular ensyme produced by S. Pyogenese
- pyrogenic exotoxin,
- is responsible for the rash seen in scarlet fever, and for other pathogenic effects of S. pyogenes. It has also been called erythrogenic toxin.
- superantigens
- which means that they induce broad T-cell stimulation and cytokine expression, like the staphylococcal enterotoxins and TSST-1
- bacitracin test
- almost all Group A streptococci are inhibited by very low concentrations of bacitracin, so if a beta-hemolytic streptococcus is found to be bacitracin sensitive, we can conclude to some degree of confidence that it is a member of Group A.
- Dick test
- to assess the patient's immune status with regard to pyrogenic exotoxin. A small quantity of toxin is injected into the skin. An erythematous reaction indicates lack of immunity, and no reaction indicates immunity. Neither of these tests is currently used for diagnostic purposes.
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Lancefeild Group A:
Streptococcus Pyogenes-
Pathology -
Direct Invasion/Toxin
1. Pharyngitis
A. Red, swollen tonsils & pharynx
B. Purulent exudate on tonsils
C. Fever
D. Swollen lymph nodes
2. Skin Infections
A. Folliculitis
B. Cellulitis
C. Impetigo
F. Necrotizing fascitis
3. Scarlet Fever: Fever & scarlet red rash on body
4. Toxic Shock Syndrome
Antibody Mediated
1. Rheumatic fever ( may follow streptococcal pharyngitis):
A. Fever
B. Myocarditis: heart inflammation
C. Arthritis: migratory polyarthritis
D. Chorea
E. Rahs: Erythema marginatum
F. Subcutaneus nodules
**10-20 years after infection, may develop perminant heart valve damage
3. Acute post streptococccal glomerulonephritis: tea-colored urine, follwoing streptococcal skin or pharynx infection -
Lancefeild Group A:
Streptococcus Pyogenes-
Treatment -
1. Penicillin G
2. Penicillin V
3. Penicillinase-resistant penicillin: in skininfections where staphlococci could be the responsible organism
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Follwoing rheumatic fever:
A. Pts placed on continuous prophylactic antibiotics to prevent repeat strep throat infections that could potentially lead to a repeat case of rheumatic fever
B. If permanent heart valve damage has occurred Ab are repquried when certain procedures are performed such as dental work) due tohigh risk of bacterial endocartditis
** For invasive streptococcus pyogenes infections such as necretizing fascitis or streptococcal toxic shock syndrome consider adding clindamycin -
Lancefeild Group A:
Streptococcus Pyogenes-
Diagnostics -
1) Gram stain: gram + cocci in chains
2) Culture on standard laboratory media. Growth is inhibited by bacitracin (S. Pyogenes is the only beta-hemolytic streptococcus which is sensitive to bacitracin) -
Lancefeild Group A:
Streptococcus Pyogenes-
Misc. -
1) Dick Test: Once commonly used to confirm Scarlet Fever Diagnosis
2) C- Carbohydrate: Used for Lancefield groupings -
Lancefeild Group B:
Streptococcus Agalactae-
Metabolism -
1)Catalase -
2) Facultative Anaerobe
3) weakly Beta-hemolytic (contrast to strong hemolytic activity of group A -
Lancefeild Group B:
Streptococcus Agalactae-
Pathology -
1) Neonatal meningitis
2) Neonatal pneumonia
3) Neonatal sepsis -
Lancefeild Group B:
Streptococcus Agalactae-
Treatment - Penicillin G
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Lancefeild Group B:
Streptococcus Agalactae-
Diagnostics -
1) Gram stain of CSF or urine
2) Culture of CSF urine or blood
-from 6% to 20% are bacitracin sensitive.
-can be presumptively distinguished from Group A streptococci by virtue of their ability to hydrolyze sodium hippurate.
Another test which can be performed to distinguish Group B from other beta-hemolytic streptococci is the CAMP test.In this test Group B streptococci enhance the hemolysis of certain staphylococci growing adjacent to them on a blood agar plate. -
Lancefeild Group B:
Streptococcus Agalactae-
Miscilaneous - -Part of normal flora 25% of pregant women carry group B streptococci in their vagina
- Lancefeild Group C & G: Facts
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-Similar to group A just a bit weaker
-some are bacitracin sensitive
-may be part of the normal flora of the pharynx, genitourinary tract, and skin.
-They can cause skin and wound infections, pneumonia, puerperal sepsis, bacteremia, endocarditis, and meningitis.