SUBMITTED TO:DR NAVNEET CHAUHAN SIR
SUBMITTED BY:DAISY ADHIKARY
BDS 2nd YEAR
ROLL NO 14
Streptococci are Gram positive cocci which
are arranged in chains. They are part of the
normal human flora. Some of them are
important human pathogens causing
pyogenic infections. They grow poorly in
simple media but their growth is enhanced by
the addition of fermentable carbohydrate
(e.g. glucose), blood or serum.
The streptococci are divided into aerobic
streptococci, obligate anaerobes and
facultative anaerobes.. Aerobic and facultative
anaerobic streptococci are classified on the
basis of their haemolytic properties. Three
types of haemolytic reactions (a, and y) are
observed on blood agar medium.
CLASSIFICATION OF STREPTOCOCCI
They produce , a greenish discolouration
around the colonies. This is due to partial
haemolysis. The zone of lysis is small (1 or
2mm wide) with presence of unlysed
erythrocytes which are detectable
microscopically. Alpha haemolysis is seen
with viridans group of streptococci and
pneumococcus.
These streptococci produce a clear, colourless
zone of complete haemolysis (2-4 mm wide)
around the colonies, within which erythrocytes
are completely lysed. The lysis of erythrocytes is
due to the production of two types of
streptolysin by the organisms: streptolysin O and
streptolysin S. The former is destroyed by oxygen
and the latter is oxygen stable.
Streptolysin S is responsible for surface colony
haemolysis.
Streptococcus pyogenes is the most important
and is responsible for many important human
infections.
THESE DO NOT PRODUCE HAEMOLYSIS IN THE
MEDIUM AND INCLUDE MOSTLY THE FECAL
STREPTOCOCCI WHICH ARE CLASSIFIED AS
THE ENTEROCOCCUS SPECIES
The individual cocci are spherical or oval, 0.5
to 1.0 µm in diameter and are arranged in
chains. Chain formation is due to successive
cell divisions occurring in one plane only and
daughter cells failing to separate completely
Streptococci are Gram positive, non-motile
and non-sporing Some strains of
Streptococcus pyogenes (Group A) and group
C have capsules composed of hyaluronic acid
They are aerobes and facultative anaerobes,
growing best at a temperature of 37°C (range
22-42°C). These are most exacting in
nutritive requirements, growth occurring only
in media containing blood, serum or 'sugars
(fermentable carbohydrates).
On blood agar, after overnight incubation, the
colonies are small (0.5- 1.0 mm, pin point),
circular, semitransparent, low convex with a
wide zone of B-haemolysis around them
In liquid media, such as glucose broth,
growth occurs as a granular turbidity with a
powdery deposit. Bacterial chains being
heavier settle down as deposit.
Streptococci are catalase negative, unlike
staphylococci which are catalase positive.
They are not soluble in 10 per cent bile,
unlike Str. pneumoniae.
Several sugars are fermented by streptococci
producing acid but no gas. These are of little
value in laboratory identification.
Streptococcus pyogenes is a delicate
organism which is inactivated by heat at 56°C
for 30 minutes. It dies in a few days in
cultures but can be stored in Robertson's
cooked meat medium at 4°C. It is rapidly
inactivated by antiseptics. It is more resistant
to crystal violet than many other bacteria,
therefore this dye is used to prepare selective
media for the isolation of streptococci. It is
susceptible to sulphonamide and many
antibiotics.
Capsule may be present on groups A and C
streptococci. The capsule when present
inhibits phagocytosis.
The cell wall is composed of an outer layer of
protein (fimbria containing protein) and
lipoteichoic acid, a middle layer of group-
specific C carbohydrate and inner layer of
peptidoglycan (mucoprotein) .
The peptidoglycan is responsible for cell wall
rigidity.
The outer part of the cell wall contains
protein antigens. Str. pyogenes is further
subdivided on the basis of their surface
proteins M, T and R.
(i) M protein:
It is the most important antigen and acts as a
virulence factor by inhibiting phagocytosis. It
is antigenic in nature.
ii) T and R protein:
The T protein is an acid labile, trypsin resistant
antigen. It may be specific, but many
different M types may have the same T
antigen
iii) Other associated factors
A non-type-specific protein associated with
the M protein is identified. This is known as
M associated protein (MAP)
1) TOXINS
i) HAEMOLYSINS:
Streptococci produce two type of
haemolysins, streptolysin 'O' and 'S'.
Streptolysin 'O' is so named because it is
oxygen labile. It is inactivated in the presence
of oxygen, but may be reactivated by
treatment with reducing substances. It is heat
labile. It lyses red cells and is also cytotoxic
for neutrophils, platelets and cardiac tissue.
Streptolysin 'S' is an oxygen stable
haemolysin and is responsible for the
haemolysis seen around colonies of
streptococci on the surface of blood agar
plates
This toxin is responsible for the rash of
scarlet fever. It is only produced by lysogenic
strains of group A streptococci.
This toxin is responsible for Dick test and
Schultz Charlton reaction. When the toxin is
injected intradermally into the skin of a
susceptible child, a localised erythematous
reaction appears. This is called the Dick
test.
In scarlet fever, when homologous antitoxin
is injected locally into the rash, blanching of
the rash occurs, it is named as Schultz
Charlton reaction
Scarlet fever is now rarely seen.
I) Streptokinase (fibrinolysin)
It promotes the lysis of human fibrin clot by
catalysing the conversion of plasminogen
(plasma precursor) into plasmin. It is protein.
in nature and antigenic. Streptokinase
facilitates the spread of infection by breaking
down the fibrin barrier around the lesions.
Group A streptococci elaborate four
antigenically distinct deoxyribonucleases
(DNAases), A,B,C and D, of which, type B is
the most antigenic in man.
These enzymes liquefy the highly viscous
DNA that accumulate in thick pus. DNA
present in pus is derived from the nuclei of
necrotic cells. This explains the thin serous
character of streptococcal exudate.
NADase acts on the enzyme NAD and
liberates nicotinamide from the molecule. It is
produced by groups A, C and G streptococci
and is antigenic. It is believed to be
leucotoxic.
It breaks down hyaluronic acid of the tissues
and favours spread of streptococcal lesion
along intercellular spaces.
Str. pyogenes produces pyogenic infections
with a tendency to spread locally. Non-
suppurative seguelae of local infections
include acute glomerulonephritis and
rheumatic fever.
(i) Respiratory infections
Sore throat (acute tonsillitis and/or
pharyngitis) is the most common of
streptococcal diseases. Tonsillitis is more
common in older children and adults
It consists of a combination of sore throat
and a generalised erythematous rash. It is
caused by a strain producing the erythrogenic
toxin. It is now rarely seen in U.K. and other
colder countries. It does not occur in India.
Str. pyogenes causes suppurative infections
of the skin with a predilection to produce
lymphangitis and cellulitis. Infection of minor
abrasions may sometimes lead to fatal
septicaemia.
The two typical streptococcal skin infections
are erysipelas and impetigo
These skin infections are the main cause
leading to acute glomerulonephritis in
children in the tropics.
Streptococcal toxic shock syndrome (TSS) is a
condition in which the entire organ system
collapses, leading to death.
Young children with chickenpox (vericella),
and elderly adults seem to be at greater risk.
Puerperal sepsis : Str pyogenes was an
important cause of puerperal sepsis. It is
used to take a heavy toll of life before
antibiotics became available.
Sepsis: Infections of skin lesions ,wounds and
burns.
Pyaemia, septicaemia,abscess in internal
organs
2) Non-Suppurative Complications
Str. pyogenes infections are sometimes
followed by two important non-suppurative
sequelae, acute rheumatic fever and acute
glomerulonephritis.
The latent period suggests an immune
response. Rheumatic fever is often preceded
my sore throat while acute
glomerulonephritis by the skin infection.
These sequelae or complications are believed
to be the result of hypersensitivity to some
streptococcal components. Rheumatic fever
may follow infection with any serotype of Str.
pyogenes while acute glomerulonephritis is
caused by only a few nephritogenic types.
Diagnosis of acute suppurative infections is
made by culture, while in the non-
suppurative complications, diagnosis is
mainly based on the demonstration of
antibodies.
1. Acute Suppurative Infections
Specimens :
Specimen is collected according to the site
of lesion, such as swab, pus, blood or CSF.
Specimens should be collected in sterile
containers under all aseptic conditions. These
should be plated immediately or sent to the
laboratory in Pike's transport medium .
(iii) Gram Staining of Smears
Gram positive cocci in chains is
indicative of streptococcal infection.
Smears are of no value where
streptococci are present as part of the
resident flora such as in infections of the
throat and genitalia.
The specimen is inoculated on blood agar medium
and incubated at 37°C for 18-24 hours. Haemolysis
develops better under anaerobic conditions or in
the presence of 5- 10% carbon dioxide. Sheep
blood agar is preferred as human blood may
contain certain inhibitors
(v Colony Morphology and Staining:
The colonies of streptococci are small 0.5- 1.0 mm
circular, low convex with a zone of B haemolysis
around them.
In liquid medium, such as glucose broth, growth
occurs as a granular turbidity with a powdery
deposit.
(vi) Biochemical Reactions:
Streptococci are catalase negative which is an
important test to differentiate streptococci from
staphylococci.
(vii) Identification of Various Groups of
Streptococci:
Group A streptococci can be rapidly identified by
fluorescent antibody technique. PYR test may be
done to differentiate Streptococcus pyogenes from
other streptococci. PYR test is positive for
Streptococcus pyogenes. Group 'B' streptococci
may be identified by the CAMP reaction
Haemolytic streptococci are grouped serologically
by the Lancefield technique. It is done for definite
classification and epidemiological studies.
(ix) Antigen Detection Tests:
ELISA and agglutination tests are used to
demonstrate group A streptococcal antigen from
throat swab.
2. Non-Suppurative Complications:
In rheumatic fever and glomerulonephritis serological
tests provide retrospective evidence of streptococcal
infection.
The routine test done is antistreptolysin (ASO) titration.
ASO titre is usually found in big levels in rheumatic
fever but in glomerulonephritis, titres tend to be low,
therefore, anti- deoxyribonuclease B (antiDNAase B)
estimation is more reliable
Antihyaluroldase is another useful test for pyoderma
infection of streptococci
Penicillin G is the drug of choice. In patients allergic
to penicillin, erythromycin or cephalexin is used.
iii) OTHER HAEMOLYTIC STREPTOCOCCI:
A. Group B Streptococci (GBS):
Str. agalactiae is an important pathogen of bovine
mastitis in cattle. In recent years, it has been
recognised as the single most important pathogen
in neonates causing neonatal septicaemia and
meningitis. It may also cause septic abortion and
puerperal sepsis.
The species Str. Dysgalactiae subsp.
equisimilis is usually isolated from human
sources. The clinical spectrum of disease
caused by this species resembles infections
caused by Str. pyogenes. It may cause human
infections like pharyngitis, skin infections,
endocarditis
Streptococci belonging to group 'D' are classified
as enterococci (faecal streptococci) and non-
enterococci (non-faecal streptococci). They are
usually non-haemolytic while some strains may be
alpha or beta haemolytic.
Group D streptococci may cause genitourinary
infection or endocarditis rarely. They are
susceptible to penicillin
Enterococci also belong to group 'D' as they contain the same
antigen as that of group 'D' streptococci. They are normal
inhabitants of human intestinal tract and possess some
distinctive properties as follows:
1) They are positive for bile- aesculin hyrolysis test.
2. They are relatively heat resistant and can withstand heat at
60° C for 30 minutes ( heat test or heat resistance test).
3) Their ability to grow in the presence of 6.5 per cent sodium
chloride.
4) Their ability to grow at 45°C and at pH 9.6.
5) They are PYR test positive.
6) They are resistant to SXT (trimethoprimsulphamethoxazole).
This group of streptococci produce alpha haemolysis on
blood agar.
They are known as viridans streptococci (from viridis
meaning green) due to greenish discolouration (a-
haemolysis) on blood agar. They are commensals of mouth
and upper respiratory tract.
They are ordinarily non-pathogenic but on occasions cause
disease. The viridans streptococci are associated with dental
caries
It breaks down dietary sucrose, producing acid and a tough
adhesive dextran. The acid damages dentine while the
dextran binds together food debris, mucus, epithelial cells
and bacteria to form dental plaques. These plaques lead to
dental caries.About 40% of subacute bacterial endocarditis is
caused by viridans group of streptococci.
