Streptocococci

8/11/2019 Streptocococci

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Streptococci (Grampositive cocci)

Lecture 45Faculty: Dr. Alvin Fox


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Key Words

Lancefield groups

Hemolysis (alpha, beta, gamma)

Group A streptococcus (S. pyogenes)

- Bacitracin susceptibility test

- M, T, R proteins

- Streptolysins O and S

- F protein/lipoteichoic acid

- Rheumatic fever/carditis/arthritis

- Glomerulonephritis

- Scarlet fever- Toxic shock-like syndrome

- Bacteremia

- Flesh-eating bacteria

- Pyrogenic toxin

- Erythrogenic toxin

Group B streptococcus (S.agalactiae)- Neonatal septicemia/meningitis

- CAMP test

- Hippurate hydrolysis test

Group D streptococcus

- Urinary tract infection

- Endocarditis

- Bile-esculin test

- Enterococci

- Non-enterococci

Large colony

Minute colony

Viridans streptococci

Dental caries/endocarditis


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Streptococcifacultative anaerobe

Gram-positive

usually chains (sometimes pairs)

catalase negative

(staphylococci are catalase positive)


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Streptococcus in chains (Gram stain)


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Streptococcus pneumoniae(diplococcus). Fluorescent stain


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Identification : Lancefield groups

- carbohydrate antigens


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groupablestreptococci

A, B and D

frequent C, G, F

less frequent


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Non-groupable

S. pneumoniae

pneumonia

viridans streptococci

e.g.S. mutans

*dental caries


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hemolysis reaction - sheep blood agar

(alpha)

partial hemolysis

green color (beta)

complete clearing

(gamma)

- no lysis

White colonies


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Hemolysis

Groups A an B

Group D

or

S. pneumoniaeand viridans


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Identification:

hemolysis reaction

+one biochemical characteristic


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Group A streptococcus (S. pyogenes)


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Group A streptococcal infections affect all ages

peak incidence at 5-15 years of age


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non-suppurative

rheumatic fever inflammatory disease

life threatening chronic sequalae

fever

heart joints

rheumatic NOT rheumatoid arthritis


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Rheumatic fever -etiology

M protein

cross-reacts heart myosin

autoimmunity

Cell wall antigens

poorly digested in vivo

persist indefinitely


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Rheumatic fever

penicillin

- terminates pharyngitis

- decreases carditis


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Acute glomerulonephritis

immune complex disease of kidney


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S. pyogenes

fibronectin

lipoteichoic acid

F-protein

epithelial cells


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M protein

M protein

fibrinogen

rr

r

peptidoglycan

rr

r

IgG

Complement IMMUNE

NON-IMMUNE


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M protein

major target

natural immunity

strain variation

antigenicity

re-infection

occurs with different strain


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Capsules

Anti-phagocytic

mucoid strains


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Isolation and identification

hemolytic colonies

bacitracin inhibits growth

hemolytic colonies

group A antigen


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Modern Rapid Strep TestThroat swab extract

(+/- streptococcal antigen)

Antibody

Liposome

+

-

Streptococcal antigen


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Post-infectious diagnosis

(serology) antibodies to streptolysin O

important if delayed clinicalsequelae occur


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Group B streptococcus

neonatal meningitis

septicemia

transmission

vaginal flora


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Group D streptococcus

Growth on bile esculin agar

black precipitate

6.5% saline

grow

enterococci

no growth

non-enterococci


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Enterococci

distantly related to other streptococci

genus Enterococcus

gut flora urinary tract infection

fecal contamination

opportunistic infections

particularly endocarditis

most common E. (S.) faecalis


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Enterococci

resistant to many antibiotics

including vancomycin

terminal D-ala replaced by D-lactate


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Minute colony streptococciVarious groups/hemolysis (e.g. group A)

genetically distinct

from large colony (e.g. S. pyogenes)

no rheumatic fever

Large colony Minute colony


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Viridans streptococci

diverse species

oral

dental caries hemolytic and negative for other tests

non-groupable.

includes S. mutans occassional endocarditis after tooth extraction

Streptocococci

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