Streptococci are classified based on oxygen requirement, hemolysis on blood agar, Lancefield carbohydrate groups, and M protein types. Streptococcus pyogenes (Group A streptococci) are aerobic, beta-hemolytic cocci arranged in chains. They cause suppurative infections like pharyngitis, impetigo, and necrotizing fasciitis, as well as non-suppurative sequelae including rheumatic fever and glomerulonephritis. Diagnosis involves culture, antigen detection, and serology. Treatment is with penicillin or erythromycin.

1. STREPTOCOCCI

2.  Cocci arrange in chain were first seen and describe by Billorth
in purulent exudates from erysipelas and infection who gave
the name streptococci.
 Streptos meaning winded or twisted.
 Rosenbach gave the name Streptococcus pyogenes to cocci
arranged in chain which is isolated from human suppurative
lesions.

3. CLASSIFICATION
 Based on oxygen requirement:
 Aerobes
 Facultative anaerobes
 Obligate anaerobes
 Based on hemolysis on blood agar:
 Alpha (α) hemolytic
 Beta (β) hemolytic
 Gamma (γ) hemolytic

4. CLASSIFICATION
 Based on carbohydrate (C) antigen:
 Lancefield groups – A to V (without I and J)
 Based on M proteins:
 Griffith typing – 80 types of S. pyogenes

7. STREPTOCOCCUS PYOGENES
- Group A streptococci
MORPHOLOGY
 Cocci, spherical or oval, 0.5–1.0 μm in diameter
 Arranged in chains
 Chain formation – cocci divide in one plane, daughter
cells fail to separate completely.

8. GROWTH CHARACTERISTICS
 Aerobes and facultative anaerobe.
 Fastidious in nutritive requirement, growth occur only in
enriched media containing blood or serum.
 Blood agar – colonies small, semitransparent, circular
with a clear zone of hemolysis around them.
 Liquid media – glucose or serum broth, granular
turbidity with a powdery deposit.

9. Blood agar: S.pyogenes showing beta hemolysis

10. BIOCHEMICAL REACTIONS
 Catalase negative (unlike staphylococci)
 Not soluble in 10% bile (unlike pneumococci)
 PYR test positive
 Ferment several sugars producing acid but no gas.

11. RESISTANCE
 Easily destroyed by heat (54°C for 30 min)
 Rapidly inactivated by antiseptics
 Resistant to crystal violet
 Selective media – crystal violet, nalidixic acid, colistin
sulphate
 Does not develop resistance to drugs
 Sensitivity to bacitracin – S. pyogenes

12. ANTIGENIC STRUCTURE
 Capsule – Group A streptococci are capsulated, made up
of hyluronic acid.
• Capsule is antiphagocytic but no antigenic.
 Cell wall:
 Outer layer – protein and lipoteichoic acid (helps in
adhesion)
 Middle layer – c carbohydrate antigen.
 Inner layer – peptidoglycan
 Peptidoglycan is responsible for cell wall rigidity.
 Serological grouping depends on the C carbohydrate
antigen. (integral part of cell wall)

13.  On the basis of carbohydrate C antigen, S.pyogenes –
Lancefield group A
 Outer layer protein layer consist of M, T and R proteins.
 Antigenic relationships have been Demonstrated between:
 Capsular hyaluronic acid and human synovial fluid
 Cell wall proteins and myocardium
 Group A carbohydrates and cardiac valves
 Cytoplasmic membrane antigens and vascular intima
 Peptidoglycans and skin antigens

15. TOXINS AND VIRULENCE FACTORS
➢ S. pyogenes forms several exotoxins and enzymes
➢ M protein act as virulence factor by inhibiting
phagocytosis
➢ C polysaccharide – toxic effect
➢ Hemolysins

16. ➢ Hemolysins:
 Streptococci produce two hemolysins, streptolysin O and S.
 Streptolysin O : oxygen labile, antigenic
 Anti streptolysin O appears in sera following streptococcal infection.
 ASO test is standard test for diagnosis of streptococcal infection.
 ASO titer in more than 200 units is considered significant and
suggests either recent or recurrent infection.
 ASO titer is more in rheumatic fever .
 Streptolysin S : oxygen stable, not anigenic.
 Protein but not antigenic, responsible for haemolysis around colonies
on the blood agar plates.

17. STREPTOKINASE (fibrinolysin)
 Promotes lysis of human fibrin clots by activating plasma
precursor – plasminogen.
 Streptokinase is given IV in treatment of early myocardial
infection & thromboembolic disorders.
DEOXYRIBONUCLEASES (streptodornase DNAase)
 Pyogenic exudates contain large amounts of DNA
 Streptodornase causes depolymerisation of DNA and helps
liquefy the thick pus
 May be responsible for the thin serous character of the
streptococcal exudates
 Useful in diagnosis of S.pyogenes infection, particularly in skin
lesions, where ASO titer is low.

18. HYALURONIDASE
 Breaks down hyaluronic acid of tissues
 This may favour spread of infection along intracellular spaces
 The enzyme is antigenic and specific antibodies appear in
convalescent sera.

19. PATHOGENICITY
 Disease – suppurative or non- suppurative (including
sequelae to post-streptococcal infections)
 S. pyogenes produces pyogenic lesions with a tendency to
spread locally along lymphatics and through blood stream.
SUPPURATIVE
1) Respiratory infections
2) Skin and soft tissue infections
3) Genital infections
NON-SUPPURATIVE (post-streptococcal sequelae)
1) Acute rheumatic fever
2) Acute glomerulonephritis

20. SUPPARATIVE COMPLICATION :
RESPIRATORY INFECTIONS
 Primary site of invasion – throat
 Sore throat – most common
 Localised – tonsillitis
 Diffuse – pharyngitis
SKIN AND SOFT TISSUE INFECTION
Two typical streptococcal infections:
▪ Erysipelas
 Diffuse infection involving the superficial lymphatics
 Affected skin red, swollen and indurated,sharply
demarcated from surrounding healthy area
 Seen in older patients

21. ▪ Impetigo
• Impetigo and streptococcal infection of scabies lesions are
the main causes of acute glomerulonephritis in children in
the tropics
 S. pyogenes causes a variety of suppurative infections of
wounds or burns, with a predilection to produce lymphangitis
and cellulitis
 Subcutaneous infections – range from cellulitis to necrotising
fasciitis
 Necrotising fasciitis – more common, caused by mixed
aerobic and anaerobic bacterial infection
 S. pyogenes M types 1 and 3 forming pyrogenic exotoxin A –
may alone be responsible – ‘flesh eating bacteria

23. Necrotising fasciitis
 Extensive necrosis of subcutaneous and muscular tissue and
adjacent fascia associated with a severe systemic illness – a
toxic shock–like syndrome, with disseminated intravascular
coagulation and multisystem failure.
GENITAL INFECTIONS
 Aerobic and anaerobic streptococci – normal inhabitants of
female genital tract
 S. pyogenes cause puerperal sepsis

24. Non suppurative complications:
 Non-suppurative post-streptococcal sequelae: two
important sequelae
 Acute rheumatic fever
 Acute glomerulonephritis
 Complications – 1 to 3 weeks after the acute infection

25. EPIDEMIOLOGY
 Streptococcal infections – respiratory tract -frequent in
children at 5–8 years of age
 More common in winter in the temperate countries
 No seasonal distribution in the tropics
 Crowding – important factor in transmission of infection
 Outbreaks in closed communities – boarding schools or
army camps

26. LABORATORY DIAGNOSIS
 Acute infections – diagnosis established by culture
 Non-suppurative complications – diagnosis based on
demonstration of antibodies.

27. Specimen
 Throat swab, pus or exudates
 In rheumatic fever and glomerulonephritis –serum sample
Microscopy
 Gram-stained films from pus – presumptive information
 Smears from throat – no value – streptococci form part of
normal resident flora

29. Culture
 Sample either plated immediately or transported in Pike’s
medium (blood agar with crystal violet and sodium azide)
 Specimen plated on sheep blood agar – incubated at 37°C
under 5–10% CO2 or anaerobically
Identification
 Hemolytic streptococci – grouped by Lancefield technique –
specific antisera
 Rapid diagnostic tests – streptococcal group A antigen
 Bacitracin sensitivity – S.pyogenes

30. Serology
 Rheumatic fever and glomerulonephritis – retrospective
diagnosis
 Antistreptolysin O titration (ASO titre) higher than 200
indicative of prior streptococcal infection
 Antideoxyribonuclease B (anti-DNAase B) higher than 300 –
significant
 Streptozyme test – sensitive and specific screening test

31. TREATMENT
 All beta hemolytic Group A streptococci are sensitive to
penicillin G
 In patients allergic to penicillin, erythromycin or
cephalexin may be used
 Tetracyclines and sulphonamides are not recommended
 Antimicrobial drugs have no effect on established
glomerulonephritis and rheumatic fever

32. OTHER HEMOLYTIC STREPTOCOCCI
 Besides S. pyogenes, streptococci belonging to groups B, C,
D, F, G and rarely H, K, O and R may also cause human
infection
 Of these B, C and G are more common
GROUP B STREPTOCOCCI :
 Important pathogens of cattle, producing bovine mastitis
 Streptococcus agalactiae – important human pathogen
responsible for:
 Neonatal infections
 Adult infections
Identified by CAMP reaction.