Dr. Tamer Bedair
Lecturer of Medical Microbiology and
Immunology
Contents:
1. Character of Streptococci
2. Classification of Streptococci
3. Strept. pyogenes
a. virulence factors and pathogenesis
b.diseases
c. lab. Daignosis
d. post Streptococcal sequelae or complication
e. treatment and prevention
4. Strept. pneumoniae (pneumococci)
5. Viridans Strept.
6. Strept. agalactia
5. Strept. faecalis (enterococci)
Causes of tonsilitis or
pharyngitis
 Group A hemolytic strept. is the
most common cause especially in
children
 Viral causes (most common in adults)
as rhinoviruses, influenza virus,
parainfluenza, adenovirus, EBV, HSV…
Characters of Streptococci
Morphology:
 Gram positive cocci
 Chains or pairs
 Pathogenis strains usually capsulated
 Non motile and Non spore forming
Culture character:
 Fastidious and grow on blood agar except strept faecalis
which is not fastidious and can grow on nutrient agar
 All Strept. need 0.03% CO2 except Strept. pneumoniae
which need CO2 5—10%
Biocemical reaction:
 All Streptococci are Catalase negative (Staphylococci are
catalase positive)
Classification
 Oxygen requirements


Anaerobic (Peptostreptococcus)
Aerobic
or
facultative
(Streptococcus)
anaerobic
 Serology (Lanciefield Classification)
 Hemolysis on Blood Agar (BA)
I-Classification of Streptococci Based on
Hemolysis on Blood Agar
Hemolysis on BA
– -hemolysis
Partial hemolysis
Green discoloration around the colonies
e.g. non-groupable streptococci (S. pneumoniae & S. viridans)
– -hemolysis
Complete hemolysis
Clear zone of hemolysis around the colonies
e.g. Group A & B (S. pyogenes & S. agalactiae)
– -hemolysis
Streptococci
No lysis
e.g. Group D (Enterococcus spp)
-hemolysis
-hemolysis
-hemolysis
Hemolysis on Blood agar
-hemolysis
-hemolysis
-hemolysis
II-Serology: Lanciefield Classification
Streptococci
Lanciefield classification
Group A
S. pyogenes
Group B
S. agalactiae
Group C
S. equisimitis
Group D
Enterococcus
Other groups
(E-U)
 Streptococci classified into many groups from A to U
 Classification based on C- carbohydrate antigen of
cell wall
 Groupable streptococci
 A, B and D (more frequent)
 C, G and F (Less frequent)
 Non-groupable streptococci
 S. pneumoniae (pneumonia)
 viridans streptococci

e.g. S. mutans
Group A streptococci =
Strept.pyogenes
Group A streptococcal infections
affect all ages but peak incidence at
5-15 years of age
The most common infection
caused by Strept. pyoenes is
pharyngitis and tonsillitis
especially in children
Pathogenesis and Virulence Factors
 Structural components
 M protein, which interferes with opsonization and
phagocytosis
 Hyaluronic acid capsule, which interferes with and
phagocytosis
 Enzymes
 Streptokinases
 Deoxynucleases
 C5a peptidase
facilitate the spread of streptococci
through tissues
 Eythrogenic toxins Produced by lysogenic
(temperate) phage and causes rash of scarlet
fever & associated with a toxic shock-like
syndrome
 Streptolysins
 Streptolysin O lyse red blood cells, white blood cells, and
platelets
 Streptolysin S
Diseases caused by Strept. pyogenes
A)Supppurative infections
B) Toxogenic diseases
C) Post streptococcal sequelae
Suppurative (pus forming)
 Pharyngitis & acute follicular
tonsilitis
 Otitis media
 Bronchopneumonia
 Bacteremia and septicemia
 Meningitis
 Skin infection, Impetigo,
Pyoderma, erysipelas and
cellulitis
Cellulitis
Impetigo
B) Toxogenic dise
1- toxic shock like syndrome -
similar in pathogenesis
and manifestation to
staphylococcal toxic shock
syndrome .
2-Scarlet fever (erythrogenic
toxin)
Usually affects
children ,characterized by
fever, skin rash &
stomatitis (Strawberry
tongue) .
The skin rash is due to
direct effect of the
erythrogenic toxin on the
skin .
Lab. diagnosis
1. sample: according to clinical disease
- tonsilitis, pharyngitis and scarlet fever: throat
swab
- erysipelas, and bacteremia: blood (blood
culture)
2. Direct microscopic examination by Gram
stain: G. +ve cocci, capsulated in long chain
3. culture: on BA, at 37 C →β hemolytic colonies
4. Colonies identification:
a. film stained by G. stain:
b. biochemical reactions: catalase -ve & bacitracin
sensitive
Diagnosis of scarlet fever
By throat swab: processed as before…… +
5-Schultz Charlton reaction (rapid diagnosis ):
-Toxin anti toxin neutralization test
-Injection of antierythrogenic toxin in the rash →
disappearance of the rash within 6-12 hours , due
to neutralization of the toxin with specific
antitoxin .
6. Dick test :
- Toxin anti toxin neutralization test
- Used to assess susceptibility of individual and
detect immunity to scarlet fever
C) Post streptococcal sequelae
 Non suppurative complication which follow strept.
pyogenes infection by 1-3 weeks
 Affect mainly in children between 5 – 15 years
 Occur following pharyngitis or skin infection
(nephrogenic strains)
 No bacteria present in pharynx at time of occurance of
the complications
 These complication includes
1. rheumatic pancarditis (rheumatic fever) with
subsequent damage in heart valves
2. glomerulonephritis
3. migratory polyarthritis
C) Post streptococcal sequelae
 Pathogenesis:
1. similarity and cross reactivity (molecular
mimicry):
M protein of Strept pyogenes is similar with heart
myosin glycoprtein so antibodies against M protein
will cross react with heart myosin glycoprtein
(autoimmunity)
2. Immune comples disease (type III
hypersensitivity):
Due to prolonged antigenemia in vivo, antigen
antibody complexes will be formed into the circulation
and precipitate on basement membrane of renal
glomeruli ten damage of renal glomeruli occur by type
III hypersensitivity
C) Post streptococcal sequelae
 Diagnosis: Jones criteria……….
 Lab. Diagnosis:
a-Non specific tests:
C- reactive protein
High ESR
b-Specific tests :
by detection of an increase in antibody titer to at least
one of the streptococcal antigens including
antistreptolysin O (ASO) which is most widely
used ,anti-DNase , antihyaluronidase& antistreptok
ASO
 aim: to determine the titre of Ab against Sterptolysin
O
 type: done in tube or on slide (passive agglutination)
 interpretation:
titre = highest dilution of serum with no
haemolysis
 titre expressed in Todd’s unit
 significant titre = 200 or more
Todd’s
unit

Treatment and prevention:
 No vaccine is available to combat S. pyogens
infections.
 The antibiotic of choice is penicillin (inhibit cell
wall peptidoglycan synthesis) or erythromycin
(inhibit 50S of ribosome)
 Long acting penicillin can be used to prevent
recurrent pharyngitis and its immune-mediated
sequelae.
Group B Streptococci
(Stretococcus agalactiae)
 Flora of vagina
 Morpholog and culture character : similar with
Strept. pyogenes
 Biochemical reaction: catalase -ve & bacitracin
resistant& CAMP test +ve
 Diseases: Neonatal septicemia , pneumonia and
meningitis
 Prevention: IV ampicillin to pregnant mothers who
have Group B in vagina.
 Diagnosis:……….
Strept. pneumoniae
 Morphology: G. +ve cocci, capsulated, in pairs, non
motile and non spore forming.
 Culture character: grow on blood agar with CO2 5—
10% (capnophilic) →αH
 Biochemical reactions: catalase –ve, optochain
sensitive, bile soluble, ferment inuline
 Virulence factors:
- main virulence is due to polysaccharide capsule →
antiphagocytic
Strept. pneumoniae
- According to polysaccharide capsule → 80 serotypes
- Humans infected by pathogenic 23 strains
- Quelling reaction: when specific Ab against capsule
bind with capsule → capsular swelling
 Diseases:
1. lobar pneumonia
2. Otitis media
3. Bacteremia and septicemia
4 Septic meningitis
Strept. pneumoniae
 Lab. Diagnosis:
sample: sputum, blood
2. Direct microscopic examination by Gram stain: G. +ve
cocci, capsulated in pairs (dipolococci)
3. culture: on BA, at 37 C →α hemolytic colonies
4. Colonies identification:
a. film stained by G. stain:
b. biochemical reactions: catalase -ve & optocain sensitive
&……….
5. Quelling reaction:………….
Strept. pneumoniae
 Treatment: penicillin or β lactam antibiotic but if
resistance suspected vancomycin can be used
 Prevention:
Polyvalent polysaccharide capsule Ag from most
pathogenic 23 strains which infect human → given to
to children & elderly & post-spleenectomy
Viridans Strept.
 Bacteria flora of oral cavity
 Morphology, culture characters: similar to
pneumococci but not capsulated
 Bioch. Reactions: catalase –ve, optochain resistant,
bile insoluble, ferment rafinose
 Diseases: dental plaques, dental caries and infective
endocarditis (on tooth extraction in patients with
heart diseas).
 Prevention: any patients with tooth extraction should
take prophylactic antibiotics before and after tooth
extraction.
Group D Streptococci
Divided into
 Enterococci (present in the intestine as flora)
 Non enterococci not present in the intestine
Enterococcus faecalis
 Flora of intestine → inducator for faecal pollution of
water
 Morphology: G+ve cocci in short chain, non
capsulated, non motile, and non spore forming
 Culture character: the only strept. which can grow on
nutrient agar & also grow on blood gar (ɣH)
 Biochemical reaction: catalase –ve & can grow in
6.5% Na Cl broth
 Diseases: UTI & intra abdominal sepsis & wound
infections
 Diagnosis: ………
 Resist antibiotics and cause nosocomial infections
Outline of differentiation between
Gram-Positive cocci
e.g. S. epidermidis
Causes of Membrane on the
tonsil
 Acute follicular tonsilitis: Strept. pyogenes………..
 Diphtheria: G +ve bacilli, in chinese letter
appearance& cultivated on loffler’s serum or blood
agar
 Oral thrush: Candida which appear as G +ve yeast &
cultivated on Sabouraud’s dextrose agar
 Vincent’s angina: B. vencenti (coiled bacteria) &
Fusbacterium (anaerobic fusiform G –ve bacilli)
 Infectious mononucleosis: EBV which diagnosed by
monospot test or Paul Bunnel test
Thanks
for your attention