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2. ⦁ Hippocrates, also known as
the father of medicine was the
fi
t
r
h
st to record scarlet fever in
4 Century B.C.
⦁ Fehleisen, in 1883, made it
clear that the causative agent
of rheumatic fever, scarlet
fever and strep throat is same
⦁ Rosenbach named it
Streptococcus pyogenes in
1884
⦁ Pasteur first isolated this chain
forming bacteria in 1879

3. ⦁ Gram positive, non motile,
non spore forming coccus
that occurs in chains or pairs
of cells
⦁ Metabolism is fermentive
⦁ Facultative anaerobe
🞂 Requires enriched medium
containing blood to grow
properly
⦁ Only species under
Lancefield's group A
Streptococcus
⦁ One of the most common
pathogen in human disease

4. Virulence factors are categorized as cell wall
antigens, toxins and enzymes
⦁ Cell wall antigens
 The cell was is composed of three layers; the inner
thick peptidoglycan layer, middle layer of group
specific C-Carbohydrate antigen and outer protein
and lipoteichoic acid layer
 In the outer protein layer three protein antigens are
observed; M, T and R proteins
 Pilli is also present
 Capsulated

5. ⦁ Toxins
 Hemolysins: Streptococci form
two hemolysins; streptolysin O,
which is an oxygen liable
streptolysin which means that
the streptolysin is inactive in
its oxidized form but can get
activated on treatment with
some mild reducing agents
and Streptolysin S which is an
oxygen stable hemolysin that
is responsible for the
hemolysis seen around the
streptococcal colonies on the
surface of blood agar plates

6.  Streptokinase: Also known as fibrinolysin,
promotes the lysis of human fibrin clots by
activating a plasma precursor
 Deoxyribonucleases: Responsible for the
depolymerisation of the DNA. The Dnases are
antigenically distinct DNases A, B, C and D, out
of these type B is most antigenic in human
beings
 Hyaluronidase: It breaks down the hyaluronic
acid of the tissues which favors the spread of
infection in the intercellular spaces

7. ⦁ Specimen Collection and Transport:
 Solely depends on the site of the lesion but
generally the specimens are collected from
throat swab, pus swab, exudates and blood
 Specimens are immediately transported after
collection or plated on Pike’s transport media
which consists of blood agar with crystal
violet and sodium azide

8. ⦁ Direct Smear Microscopy:
 Gram staining of pus swab
shows gram positive cocci in
chain
 In case of using throat swab
direct microscopy is not much
useful because in that case
Streptococcus pyogenes
becomes a part of the normal
flora in the sample
⦁ Culture:
 Blood Agar: Colonies formed as
small, pinpoint, circular,
semitransparent and with a
wide zone of β hemolysis
 Liquid media: Glucose, serum
broth or brain heart infusion
broth is used and the growth
appears as granular turbidity
with powdery deposit

9. ⦁ Selective media:
 Crystal violet blood agar: 0.1%
Crystal violet prevents the growth
of other bacteria and promotes
only the growth of S. pyogenes
 PNF media: Composed of horse
blood agar with polymyxin B,
neomycin and fusidic acid. These
antibiotics do not allow other
microorganisms to grow
⦁ Biochemical tests for
identification:
 Catalase test: This test helps in
differentiating between catalase
positive and catalase negative
bacteria where, streptococci are
catalase negative

10.  Bacitracin sensitivity testing:
This test helps in
differentiating between group
A and group B Streptococcus.
The group A Streptococcus are
sensitive to bacitracin 0.04 U
disk whereas the group B
Streptococcus are resistant to
it. Any zone of inhibition
around the disk is considered
as a positive test. It can be
used as a rapid diagnostic test
for Group A Streptococcus