Here's a little information about a very common pathogen in human diseases Streptococcus pyogenes. This presentation consists of the history of the organism, its introduction, its morphology, the cell antigens and proteins, the diseases caused by this organism its diagnosis and treatment. I hope it is helpful for the people studying medical microbiology.

1. Presented by:
Ruchira Banerjee

2.  Hippocrates, also known as
the father of medicine was the
first to record scarlet fever in
4th 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.  Streptococcal Pyrogenic Exotoxin: Also known as
erythrogenic toxin because it produces
erythematous reactions in the skin which is used
to identify scarlet fever
 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

7.  Nicotinamide Adenine Dinucleotidase: It acts on
the coenzyme NAD and liberates nicotinamide
which is antigenic and specifically neutralized by
convalescent sera
 Hyaluronidase: It breaks down the hyaluronic
acid of the tissues which favors the spread of
infection in the intercellular spaces
 Serum Opacity Factor: Some types of S. pyogenes
produce lipoproteins that creates an opacity
when applied on agar gel containing horse or
swine serum. It is a virulence determinant of the
organism

8. Streptococcus pyogenes
is responsible for two
major respiratory tract
disease. Throat is the
primary site where the
invasion occurs and
the infection occurs
through respiratory
droplets. The diseases
caused are:
 Pharyngitis
 Scarlet Fever

9.  Also known as Sore throat
 Most common streptococcal
disease
 Either in localized form or in
diffused form
 Characterized by erythema
and swelling of pharyngeal
mucosa with pus secreting
exudate formation
 Children less than the age of
3 years are manifested with
a syndrome of fever, malaise
and lymphadenopathy
without exudative
pharyngitis

10.  Pharyngitis gets complicated when the infection
spreads from the pharynx to deeper tissues by
direct
 When the infection spreads through
hematogenous or lymphatic routes, it leads to
diseases like sinusitis, meningitis, bacteremia
etc.

11.  Also known as Scarlatina
 Mainly affects children
between the age of 5 years to
15 years
 Earlier it was a very common
childhood disease but now has
become rare
 It is a contagious disease that
can spread even through
touch
 Mediated due to streptococcal
toxins SPE-A, B, and C

12.  Major characteristic is
pharayngitis
 Bright red rashes on skin
having a sand paper like
texture
 Rashes are either due to
direct action of the
circulating toxin or due to
hypersensitivity reaction
 Strawberry tongue i.e., a
tongue with large red
dots
 Rashes in skin folds
known as the Pastia’s
lines

13.  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

14.  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

15.  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

16.  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

17.  All the beta hemolytic group A streptococci
are sensitive to penicillin G
 Majorly sensitive to Erythromycin
 Patients allergic to penicillin G and
Erythromycin are treated with Cephalexin
 Tetracyclines and sulphonamides are not
recommended at all
 Bacitracin is used for local application on skin
lesions