Download Streptococcus pyogenes

Bacteriology
lecture no. 2
Streptococcus
*General characteristic
1-All species of this genius is catalase negative ,gram positive ,
cocci.
2-it is characteristically form pairs or chains during growth.
3- They are widely distributed in nature ,some are members of
the normal human flora ,others are associated with important
human diseases attributable in part to sensitization to them .
4-streptococci elaborate a variety of extracellular substances and
enzymes .
*Classification of Streptococci.
The classification of streptococci into major categories has been
based on a series of observations .
1- Colony morphology and hemolytic reactions on blood agar .
2- Serological specificity of the cell wall group – specific
substances and other cell or capsular antigens .
3- Biochemical reactions and resistance to physical and
chemical factors .
4- Ecologic features .
a- *Hemolysis .
Many streptococci are able to hemolysis RBC in vitro in
varying degrees , complete disruption of RBC with
cleaning of the blood around the bacterial growth is
called β hemolysis, incomplete lysis of RBC with
reduction of hemoglobin and the formation of green
pigment is called α hemolysis , other streptococci are
nonhemolytic sometimes called ƴ hemolysis .
B- Group – specific substances ( Lancefield
classification )
This CHO is contained in the cell wall of many
streptococci and forms the basis of serologic grouping
into Lancefield group A-H and K-u . The serologic
specificity of the group – specific CHO is determined by an
amino sugar .
C – Capsular polysaccharides .
The antigenic specificity of the capsular polysaccharides is used to classify S.pneomoniae into over 90
types and to type the group β streptococci ( S.agalactiae )
D – Biochemical reactions .
Biochemical tests include sugar fermentation
reactions tests for the presence of enzymes , and tests
for susceptibility or resistance to certain chemical agents .
*characteristics of medically important streptococci .
Name
Streptococcus
pyogenes
Groupspecific
substance
A
Streptococcus
agalactiae
B
Streptococcus
dysgalactiae
C,G
Enterococcus
faecalis
D
hemolysis Habitat
Important
criteria
β
Throat, skin
None , α
Colon
Pharyngitis, impetigo
rheumatic
fever,
glomerulonephritis
toxic shock
Neonatal sepsis and
meningitis
,
bacteremia in adults
Pharyngitis pyogenic
infection – similar to
group A streptococci
Growth in presence Abdominal obsess UTI
ƴ bite , hydrolyze , endocarditis
esculin , growth ,in
6.5%NaCl
,PYR
+ve
Dental
caries
,endocarditis
,abscess
Large colonies ,
PYR test positive ,
inhibited
by
bacitracin
β
Female genital tract , lower Hippurate
GI tract
hydrolysis (Amppositive)
β (human) Throat
Large colonies
α or none
Viridans
Usually not None,α
streptococci
typed
or
have
many untypeable
species
Streptococcus
pneumoniae
None
tab, Common
and
important diseases
Α
Mouth,throat,colon,female
genital tract.
nasopharynx
Susceptible
to Pneumonia, meningitis
optochin ,colonies ,endocarditis,
otitis
soluble in bile, media, sinusitis
quelling
reaction
positive
*Streptococcus pyogenes
- most Streptococci that contain the group A antigen are S.
Pyogenes .
- it is the main human pathogen associated with local or
systemic invasion and post streptococcal immunologic
disorders ,
- S Pyogenes typically produces large zones of β-hemolysis
around colonies greater than 0.5 mm in diameter .
- they are PYR – positive and usually are susceptible to
bacitracin .
*morphology and identification .
A- Typical organisms .
1- Individual cocci are spherical or ovoid and are arranged in
chains .
2- The members of the chain often base a striking diplococcal
appearance , the lengths of the chain vary widely and are
conditioned by environmental factors .
3- Streptococci are gram positive , however , as a culture ages
and the bacteria die, they lose their gram positivity .
4- Most group A strains produce capsules composed of
hyaluronic acid . This impede phagocytosis .
5- The capsule binds to hyaluronic – acid – binding protein ,
CD44 present on human epithelial cell ,Binding induces
disruption of intercellular junctions allowing m.o. , to remain
extracellular of intercellular junctions allowing m.o. to
remain extracellular as they penetrate the epithelium .
B- culture :1- Most streptococci grow in solid media as discoid colonies
usually 1-2 mm in diameter .
2- It is typically β- hemolytic .
C- Growth characteristics ,
1- Energy is obtained principally from the utilization of glucose
with lactic acid as the end product .
2- Growth of streptococci tends to be poor on solid media or in
broth unless enriched with blood or tissue fluids .
3- Most pathogenic hemolytic streptococci grow best at 37C0 .
4- Most streptococci are facultative anaerobes and can grow
under anaerobic conditions .
*Antigenic
structure
:-
A- M protein
- This substance is a major virulence factor of group A
S.pyogenes. M protein appears as a hair like projection of
the streptococcal cell wall . when M protein is present, the
streptococci are virulent, and in the absence of M type –
specific antibodies , they are able to resist phagocytosis by
polymorphonuclear leucocytes . S. Pyogenes that lack m
protein are not virulent .
- There are many , types of M protein may reach to 150 types
and this explain why a person can’t develop immunity
against Streptococcal pyogenic infection .
- It appears that m protein and perhaps other streptococcal
cell wall antigens have important role in the pathogenesis of
rheumatic fever .
- A component of the cell wall of selected M types induces
antibodies that react with cardiac muscle tissue .
B- T substances . this antigen has no relationship to virulence
of streptococci unlike m protein , T substance is acid labile and
heat – labile .
C- Nucleoproteins . Extraction of streptococci with weak
alkali yield mixtures of proteins and other substances of little
serologic specificity , called P substances , which probably
make up most of the streptococcal cell body .
*Toxins and Enzymes .
More than 20 extracellular products that are antigenic are
elaborated by S. Pyogenes , including the following .
A- Streptokinase ( fibrinolysin )it is produced by many strains
of group A –βhemolytic streptococci , it transforms the
plasminogen of human plasma into plasmin , an active
proteolytic enzyme that digest , fibrin and other proteins , it
has been given intravenously for treatment of pulmonary
emboli, coronary artery , and venous thrombosis .
B- Streptodornase or streptococcal deoxyribon nuclease ,
which depolymerizes DNA . purulent exudates owe their
viscosity largely to deoxyribonucleorprotein , so this enzyme
help to liquefy exudates and facilitate removal of pus and
necrotic tissue , antimicrobial drugs thus gain better access ,
and infected surfaces recover more quickly .
C- Hyluronidase : it splits hyaluronic acid , an important
component of the grand substance of connective times . it
aids in spreading infecting microorganisms . (spreading
factor) it is antigenic and specific for each bacterial or tissue
source .
D- Pyrogenic exotoxins ( Erythrogenic Toxin )
These toxins are elaborated by S.pyogenes . There are 3
antigenic ally distinct Streptococcal pyrogenic exotoxins A,B
and C. The streptococcal pyrogenic exotoxins have been
associated with streptococcal toxic shock syndrome and
scarlet fever , and most case is associated with type A , some
rare cases may be attributed to type C while the role of type
C is unclear .
The pyrogenic exotoxins act as superantigens , which
stimulate T cells by binding to the class 2 major
histocompatibility complex in the VB region of the T cell
receptor and the T cell release cytokines that mediate shock
and tissue injury .
E- Diphophopyridine Nucleotides .
This enzyme is elaborated into the environment by some
streptococci ,and this substance may be related to the
organism’s ability to kill leukocytes .
F- Hemolysins :
The β- hemolytic group A S Pyogenes elaborates two
hemolysin streptolysin O , it is hemolytically active in the
reduced state and rapidly inactivated in the presence of
oxygen , it is responsible for some of the hemolysis seen in
blood agar , and it combines with antistreptolysin O (ASO) ,
an antibody that appears in humans following infection with
any streptococci that produce streptolysin O , an ASO serum
titer in excess of 160 – 200 units is considered abnormally
high .
- Streptolysin S .Is the agent responsible for the hemolytic
zones around streptococcal colonies growing on the surface
of blood agar plates , it is not antigenic and elaborated in the
presence of serum .
*pathogenesis and clinical findings :A variety of distinct disease processes are associated with S
Pyogenes infections , the infection can be divided into several
categories .
A- Diseases attributable to invasion by S. Pyogenes ,β.
Hemolytic Group A streptococci , the portal of entry
determine the principal clinical picture .
1- Erysipelas :- if the portal of entry is the skin , erysipelas
results , with massive brawny edema and a rapidly
advancing margin of infection .
2- Cellulitis :- streptococcal cellulitis is an acute rapidly
spreading infection of the skin and subcutaneous tissues , it
fallows infection associated with mild trauma , burns ,
wounds or surgical incisions .
3- Necrotizing fasciitis (streptococcal gangrene ) there is
extensive and very rapidly spreading necrosis of the skin and
subcutaneous tissue this is infection of subcutaneous tissues
and fascia .
4- Puerperal fever :- if the streptococcal enter the uterus after
delivery, puerperal fever develop .
5- Bacteremia sepsis :- infection of traumatic or surgical wands
with streptococci results in bacteremia , which rapidly can
be fatal .
B- Diseases attributable to local infection with S. Pyogenes and
their by product .
1. Streptococcal sore throat :- it is the most common
infection due to β-hemolytic streptococcal Pyogenes
adhere to the pharyngeal epithelium by means of
lipoteichoic acid-covered surface pili and also by means of
hyaluronic acid in encapsulated strains . S. Pyogenes
infection of the upper respiratory tract doesn’t usually
involve the lungs , pneumonia when occur , is rapidly
progressive and severe and is most commonly a sequela to
viral infection e.g. influenza or measles , which seems to
enhance susceptibility greatly .
2. Streptococcal pyoderma.
- Local infection of superficial layers of skin , especially in
children is called impetigo , it consist of superficial vesicles
that break down and eroded areas whose denuded surface
is covered with pus and later is encrusted . group A
streptococcal skin infections are often attributable to M type
49,57 and 59-61 and may precede glomerulonephritis but do
not often lead to rheumatic fever .
C- Invasive group A streptococcal infections , streptococcal
toxic shock syndrome , and scarlet fever ,
Fulminant invasive S.pyogenes infections with streptococcal
toxic shock syndrome are characterized by shock , bacteremia
respiratory failure , and multiorgan failure , death occurs in
about 30% of patients , the infections tend to follow minor
trauma in otherwise healthy persons with several
presentations of soft tissue infection , such as necrotizing
fasciitis , myositis , bacteremia occurs frequently .
Pyrogenic exotoxins A-C also cause scarlet fever in
association with S Pyogenes pharyngitis or with skin or soft
tissue infection. The pharyngitis may be severe , the rash
appears on the trunk after 24 hour of illness and spreads to
involve the extremities .
D- Post streptococcal diseases (Rheumatic fever , Glomerulinephritis) . following an acute S. Pyogenes infection , there is
a latent period of 1-4 weeks , after which nephritis or
rheumatic fever occasionally develops . the latent period
suggest that the post streptococcal diseases are not
attributable to the direct effect of disseminated bacteria but
represent instead a hypersensitivity response . Nephritis is
more commonly preceded by infection of the skin , rheumatic
fever is more commonly preceded by infection of the
respiratory tract .
Rheumatic fever is the most serious sequel of S. Pyogenes
because of results in damage to heart muscle and valves
certain strains of group A streptococci contain cell
membranes antigens that cross – react with human heart
tissue antigens .
*Streptococcal pneumonia
*General characteristics :
1- It is gram-positive diplococci , often lancet – shaped
arranged in chains .
2-It possess a capsule of polysaccharide that permits typing
with specific antisera .
3- Pneumococci are readily lysed by surface – active agents ,
which probably remove or inactivate the inhibitors of cell
wall autolysins .
4- Pneumococci are normal inhabitants of the upper
respiratory tract of 15-40 % of human .
5- It can cause pneumonia , sinusitis , bronchitis , bacteremia
meningitis and other infections processes .
*morphology and identification .
A- Typical organisms .
- It is gram positive , lancet shaped diplococcic are often
seen in young culture .
- In sputum or pus single cocci or chains are also seen.
- Autolysis of pneumococci is greatly enhanced by surface –
active agents .
- Lysis occurs in a few minutes when ox bile (10%) or sodium
deoxycholate (2%) is added to a broth culture , while
viridians streptococci don’t lyse and are thus easily
differentiated from pneumococci .
- Growth of pneumococci is inhibited around a disk of opto chin .
B- Culture .
- Pneumococci form small round colonies , at first dome –
shaped and later developing a central plateau with an
elevated rim .
- It is α-hemolytic on blood agar . Growth is enhanced by
5-10 % , CO2
C- Growth characteristics .
- Most energy is obtained from fermentation of glucose . this
is accompanied by the rapid production of lactic acid , which
limit growth .
- Neutralization of broth cultures with alkali at intervals
results in massive growth .
D-Variation :
- Pneumococcal isolates that produce large anoints of
capsules produce large mucoid colonies .
- Capsule production is not essential for growth an agar
medium so it lost after a small number of subculture .
*Antigenic structure :
A- component structures :
- The pneumococcal cell wall has peptidoglycan and teichoic
acid , like other streptococci .
- The capsular polysaccharide is covalently bound to the
peptidoglycan and the cell wall polysaccharide .
- The capsular polysaccharide is immunologically distinct for
each of the more than 90 types .
B-Quelling Reaction :
- When pneumococci of certain type are mixed with specific
anti polysaccharide serum of the same type or with polyvalent antiserum on a microscope slide , the capsule results
markedly and the organisms agglutinate by cross-linking of
the anti-bodies .
- This reaction is useful for rapid identification and for typing
of the organism , either in sputum or in cultures .
- The polyvalent antiserum , which contains anti-body to all
of the types is a good reagent for rapid microscopic
determination of whether or not pneumococci are present
in fresh sputum .
*pathogenesis :
-
-
-
A- Types of pneumococci :
In adults , types 1-8 are responsible for about 75% of cases
of pneumococcal pneumonia and for more than more than
half of all fatalities in pneumococcal bacteremia .
In children , types 6 , 14 , 19 and 23 are frequent causes .
B- production of disease :
Pneumococci produce disease through their ability to
multiply in the tissues , they produce no toxins of
significance ,
The virulence of the organism is a function of its capsule ,
which prevents or delays ingestion by phagocytosis .
C- Loss of natural resistance :
- Since 40-70 % of humans are at some time carriers of
virulent pneumococci , the normal respiratory mucosa may
possess great natural resistant to the pneumococci .
- The predisposing factor for infection with pneumococci are
the following .
1- Viral and other respiratory tract infections that damage
surface cells , abnormal accumulations of mucous product
pneumococci from phagocytosis .
2- Alcohol or drug intoxication , which depresses
phagocytosis depresses the cough reflex and facilitates of
foreign material .
3- Abnormal circulatory dynamics e.g. heart failure .
4- Other mechanism e.g. malnutrition , general debility ,
stickle cell anemia ,hyposplenism , nephrosis or
complement deficiency .
*Diseases they produce :
1- pneumonia . 2- sinusitis. 3- otitis media . 4- meningitis
5- Bacteremia . 6- Septic arthritis 7- endocarditis .
- The types of meningitis that caused by Streptococcal
pneumonias called pneumococcal meningitis to differentiate
it from meningococcal meningitis that are caused by
Neisseria meningitidis .
*Enterococci*
*General characteristics .
1- Gram positive cocci .
2- They have the group D. group – specific substance and
were previously classified as group D streptococci .
3- The structure of group D cell wall specific antigen is a
teichoic acid , and this substance is not an antigenically
good marker , enterococci are usually identified by
characteristics other than immunologic reaction with group
specific antisera .
4-They are usually part of the normal enteric flora .
5- They are usually non hemolytic , but occasionally αhemolytic .
6- Enterococci are PYR + ve .
7- They group in the presence of bile and hydrolyze esculin
(bile esculin – positive ) .
8- They group in 6.5 % Nacl .
9- They grow well at between 10C0 and 45C0 whereas
streptococci group at a much narrower temperature
range .
10- They are more resistance to penicillin G then the
streptococci , and rare isolates have plasmids that
encode for β-lactamase .
11- Many isolates are vancomycin – resistant .
12- They are at least 12 species of enterococci ,
Enterococcus foecalis is the most common species and
cause 85 – 90 % of enterococcal infections , while
Enterococcus faecium cause 5-10% .
13- They are among the most frequent causes of
nosocomial infections , particularly in intensive care unit .
14- Enterococci are transmitted from one patient to
another primarily on the hands of hospital personnel ,
Enterococci , occasionally are transmitted on medical
devices .
15- In patients , the most common sites of infection are
the urinary tract , wounds, biliary tract , and blood .
16- Enterococci may cause meningitis and bacteremia in
neonates , in adults it may cause endocarditis .
17- A major problem with the enterococci is that they can
be very resistant to antibiotics .
18- E. faecium is usually much more resistant to antibiotic
than E. foecalis .
19- Enterococci are intrinsically resistant to cephalosporin ,
penicillin , and monobactam , they have intrinsic low –
level resistant to many aminoglycosides one of
intermediate susceptibility to fluoroquinolones and are
less susceptible than streptococci to penicillin and
ampicillin .
20- The glycolpeptide vancomycin is the primary drug to a
penicillin aminoglycoside for treating enterococcal
infections and vancomycin resistance phenotypes are
increased in frequency .
The end