Title of Lecture: The Streptococci
Date of Lecture: 9-11-2014
Sheet no: 13
Refer to slide no. : 7
Written by: Siwar Al-ashhab
Slide #2
*General Characteristics :
- A diverse collection of gram positive cocci typically arranged in pairs or chains ( morphology )
- Their size = 1 micron in diameter
- Most species are facultative anaerobes but some are anaerobes or capnophilic ( growth
dependent on CO2 , a little bit of carbon dioxide is added to their atmosphere in order to grow )
- Their nutritional requirements are complex, necessitating the use of blood or serum – enriched
media for isolation.
- They are catalase negative ( the catalase enzyme catalyzes the hydrogen peroxide to water and
oxygen but here in streptococci the hydrogen peroxide stays as it is , so its known as catalase
negative ) .
- so the catalase reaction is used as a way of differentiation in the cocci .
Slide #3
you have to know that the streptococci grow in chains .
Slide #4
-
They are more complicated than staphylococci
-
Three different schemes are still used to classify the organisms:
1) Serological properties (Lancefield grouping A through H, K through V)
2) Hemolytic patterns (α, β, ɣ) , the mostly used .
3) Biochemical properties.
-
Hemolytic patterns
As we know the streptococcus grow on a blood agar , If the colony :
A ) lyses the RBC’s completely and produce an empty white area around it “ clear zone
“ it is called Beta-hemolytic Streptococci .
B) lyses the RBC’s partially and produce a green area around it , it is called Alphahemolytic Streptococci .
C) doesn’t lyse any of RBC’s ( no green or white colour ) , it is called non-hemolytic
streptococci . ( Gamma-hemolytic Streptococci ) .
-
Beta-hemolytic streptococci can be further classified according to serology by using antibodies against a certain antigen “ carbohydrate antigens “
examples of these antigens : * type A because they bind to anti-A serum (antibodies
specific for them
* type B because they bind to Anti-B serum (antibodies Specific for them )
* we have also type C, G , E but the most common types are A and B
Slide #5
Group A Beta Hemolytic Streptococci
-
they have carbohydrate antigen type-A , and they are the most important one
- Also called Streptococcus pyogenes.
-
An important cause of a variety of suppurative and non suppurative diseases
“ suppurative disease : a disease cause the production of a pus “
- The most common cause of bacterial pharyngitis.
- They may cause dramatic life – threatening diseases .
“ these disease can be as a direct cause by the bacertia or by toxins they produce or by a
delayed complications of bacterial infections .
-
Form short chains in clinical specimens and longer chains when grown in liquid media
Slide #6
Antigenic Structures
- Group – Specific Carbohydrate : 10% of the dry weight of the cell , present on the surface
and they are detected by the antibodies
In addition to the carbohydrate antigens , we have “ Type – Specific Proteins “ :
- M-protein: a major type – specific protein associated with virulent streptococci. More than
80
serotypes , it is really a pathogenecity factor because :
a) it has a virulence factors “ cause a broad range of infections
b) it prevents the complement activation on the surface of streptococcus by binding the Hfactor .
“ H-factor : is a member of the regulators of complement activation family , which
regulates the Alternative Pathway of the complement system, ensuring that the
complement system is directed towards pathogens ( the bacterial cell ) and lyses it , or
opsonizes it ( for the phagocytosis ) “
- I Protein: trypsin resistant of unknown function
- M-like proteins: similar to M protein
- F protein: binds fibronectin .
- Capsule: hyaluronic acid , is not antigenic ( there’s no antibodies that are produced against
them , because it is made of hyaluronic acid which presents normally in our body “self-antigen
“ , But it is a pathogenecity factor )
Slide # 7
Pathogenesis
- Lipoteichoic acid: binds to fibronectin
- Capsule: antiphagocytic
- M protein:
- antiphagocytic.
- Binds factor H which destabilizes C3b and degrades it
- Specific M protein serotypes are associated with
rheumatic heart disease and glomenrulonephritis ( immunological complications ) .
- M –like proteins: bind Fc of IgG and IgA and α2 – macroglobulin ( it prevents the
antibodies from doing their functions )
- F – Protein: a receptor for fibronectin ( it is an adhesive factor that binds to fibronectin in
tissues ) .
Slide #8
Toxins produced by Streptococci :
1)
Pyrogenic Exotoxins (erythrogenic toxins)
- Three immunologically distinct heat- labile
toxins; A, B and C
- Act as superantigens releasing IL-1, IL-2, IL-6, TNFα , and IFN. ( superantigens : antigens
that activate lots of T-cells non-specifically and produces a lot of cytokines which lead to
serious condition = septic shock ‘ septicemia ‘ and death .
- Responsible for the rash of scarlet fever.
2) Streptolysins S and O , it cause the lysis of the RBC’s and produces Pus .
( S: stable in the prescence in the oxygen , O : oxygen labile )
3) Streptokinase: two forms A and B , it breaks the blood clot so it is used widely in
hospitals as an anti-platelets in emergencies , in ischemic stroke for example .
Slide #9
4) Deoxyribonuclease: four types A through D.
5) C5a peptidase: inhibit the function of C5a.
-Other Enzymes: hyaluronidase and diphospho -pyridine nucleotidase.
- Alpha hemolytic and non hemolytic streptococci are able to produce antibiotic – like
substances called bacteriocins which suppress the growth of group A streptococci.
Slide#10
- Clinical syndromes : by Beta-hemolytic Streptococci
- Suppurative Streptococcal Disease
- Pharyngitis
- Develops 2-4 days after exposure with an abrupt onset of sore throat, fever, malaise and
headache.
- Posterior pharynx appears erythematous with an exudate and cervical lymphadenpathy.
- Peritonsillar and retropharyngeal abscesses are rare.
- Pharyngeal carriage among school children can be as high as 20%.
Slide #11
Scarlet Fever
- A complication of streptococcal pharyngitis.
- Within 1 to 2 days of the development of pharyngitis.
- A diffuse erythematous rash initially appears on the upper chest and then spreads to the
extremities.
- The area around the mouth is generally spared.
- The rash disappears in 5 to 7 days and is followed by desquamation.
- it may change the shape of the tongue , it will look alike a strawberry
“ Not everyone affected by the streptococci infection will get the scarlet fever “
Slide #15
Pyoderma (impetigo)
- a confined infection of the skin that primarily affects exposed areas (face, arms, legs).
- Vesicle → pustule → rupture and crust over.
- Secondary spread.
- Affects young children (2-5 years) with poor personal hygiene and occurs during the
warm, moist summer months.
- Different strains from those causing pharyngitis
Slide #16
Erysipelas (erythros = red, pella = skin )
- Local pain and inflammation, lymph node enlargement and systemic signs (chills, fever,
leukocytosis).
- Involved area is typically raised and distinctly differentiated from the uninvolved skin.
- Occurs most commonly in young children or older adults more commonly on the legs
(face in the past).
- Usually preceded by respiratory tract or skin infection with group A streptococci.
Slide #19
Cellulitis
Necrotizing Fasciitis
- An infection that occurs deep in the subcutaneous tissue and go under the skin and spread
into the fascia.
- Characterized by an extensive destruction of muscle and fat that spreads along the fascial
planes , and these are very serious infection , because it leads to necrosis , toxemia then septic
shock and the patient may die .
- The organism (flesh – eating bacteria) is introduced into the tissue through a break in the
skin and it may cause extensive destruction for the tissue .
Slide #20
- Initially there is evidence of cellulitis, after which bullae form and gangrene and systemic
symptoms develop
- Systemic toxicity, multiorgan failure and death (>50%) are the hallmarks of this disease.
- Prompt therapy is necessary by aggressive surgical debridement of non viable tissue and
antibiotics.
Slide #21
Streptococcal Toxic Shock Syndrome
- Similar to that of staphylococci (skin infection with multi- system toxicity).
- Those with underlying disease are at an increased risk.
- M protein serotypes 1, 3, 12 or 28 are most common.
- It is associated with erythrogenic toxins.
Slide # 22
Other Diseases
Puerperal sepsis ( child bed fever or post partum endomyometritis that is a condition
that
results from an infection of the female reproductive organs ) and lymphangitis .
-
Pneumonia - Bacteremia: common in patients with necrotizing fasciitis or toxic shock
syndrome
(40%)
Non suppurative Streptococcal Disease ( No pus )
- Rheumatic fever (M types 18, 3, 5) : is an inflammatory disease that occurs
following
A Streptococcus pyogenes infection . ( when somebody got the infection by
Streptococcus the
body will produce antibodies against the M-proteins and they will eradicate the infection ,
but
unfortunately after one to three weeks from the beginning of the disease you will find in some
people that these antibodies that are produced against the M-proteins cross-react with antigens on
the heart valves [ because the antigen on the streptococcus are similar to those on heart valves ]
so , it will cause inflammation of heart valves which leads to endocarditis ) and its is known as
rheumatic fever ‘autoimmune disease ‘ .
- Acute glomerulonephritis (M types 12,4,2,49,59,61)
Some of the antigens of streptococcus will be secreted into the blood , and antibodies will be
produced against them , the antibody-antigen complexes will precipitate in places like
kidney’s small blood vessels which lead to kidney inflammation which is called
glomerulonephritis
( immunologic cause )

but the inflammation in the kidney which is caused by a bacteria we called “
pyelonephritis “
Good Luck :D