Streptococci

STREPTOCOCCI Faculty: Dr. Alvin Fox

1

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 2

• Streptococci

– facultative anaerobe – Gram-positive – usually chains (sometimes pairs) – catalase negative (staphylococci are catalase positive)

3

Streptococcus in chains (Gram stain)

4

Streptococcus pneumoniae (diplococcus). Fluorescent stain

5

Identification : Lancefield groups - carbohydrate antigens

6

groupable streptococci • A, B and D – frequent

• C, G, F – less frequent

7

Non-groupable • S. pneumoniae – pneumonia

• viridans streptococci – e.g. S. mutans * dental caries 8

hemolysis reaction - sheep blood agar • α (alpha) – partial hemolysis – green color • β (beta) – complete clearing White colonies

• γ (gamma) - no lysis 9

Hemolysis • Groups A an B –β

• Group D – α or γ

• S. pneumoniae and viridans –α 10

Identification: hemolysis reaction + one biochemical characteristic

11

Group A streptococcus (S. pyogenes)

12

Group A streptococcal infections affect all ages peak incidence at 5-15 years of age

13

S. pyogenes -suppurative • non-invasive – pharyngitis – skin infection, impetigo

• invasive bacteremia – toxic shock-like syndrome – "flesh eating" bacteria – pyrogenic toxin 14

Pyrogenic toxin • • •

superantigen T cell mitogen activates immune system

15

Scarlet fever • rash • erythrogenic toxin

16

non-suppurative • rheumatic fever – – –

inflammatory disease life threatening chronic sequalae • fever • heart • joints

• rheumatic NOT rheumatoid arthritis

17

Rheumatic fever -etiology • M protein – cross-reacts heart myosin – autoimmunity

• Cell wall antigens – poorly digested in vivo – persist indefinitely

18

Rheumatic fever • penicillin - terminates pharyngitis - decreases carditis

19

Acute glomerulonephritis • immune complex disease of kidney

20

Major pathogenesis factors • lipoteichoic acid/F protein – fimbriae – binds to epithelial cells

• M protein – anti-phagocytic

21

S. pyogenes lipoteichoic acid F-protein

fibronectin

epithelial cells 22

M protein IMMUNE

Complement IgG

r

r

M protein

r

NON-IMMUNE

peptidoglycan

fibrinogen

r

r

r

23

M protein • major target – natural immunity

• strain variation – antigenicity

• re-infection – occurs with different strain

24

Capsules • Anti-phagocytic – mucoid strains

25

Isolation and identification • β hemolytic colonies – bacitracin inhibits growth

• β hemolytic colonies – group A antigen 26

β hemolysis • hemolysin O – sensitive oxygen

• hemolysin S – insensitive oxygen

27

Modern Rapid “Strep” Test Throat swab extract (+/- streptococcal antigen)

-

+ Antibody Liposome Streptococcal antigen

28

Post-infectious diagnosis (serology) • antibodies to streptolysin O • important if delayed clinical sequelae occur

29

Typing Traditional serotyping of proteins: -M -T -R Current: - Sequencing of M protein gene 30

Group B streptococcus • • •

neonatal meningitis septicemia transmission – vaginal flora

31

Group B streptococcus - identification • β hemolysis • hippurate hydrolysis • CAMP reaction – increases β hemolysis of S. aureus

32

Group D streptococcus • Growth on bile esculin agar – black precipitate • 6.5% saline • grow – enterococci • no growth – non-enterococci 33

Enterococci • • •

distantly related to other streptococci genus Enterococcus gut flora – urinary tract infection • fecal contamination

– opportunistic infections • particularly endocarditis

• most common E. (S.) faecalis 34

Enterococci • resistant to many antibiotics – including vancomycin • terminal D-ala replaced by D-lactate

35

Minute colony streptococci Various groups/hemolysis (e.g. group A) – genetically distinct from large colony (e.g. S. pyogenes) – no rheumatic fever

Large colony

Minute colony

36

Viridans streptococci • • • • • •

diverse species oral dental caries α hemolytic and negative for other tests non-groupable. includes S. mutans – occassional endocarditis after tooth extraction

37