Strep throat is caused by infection with a bacterium known as Streptococcus pyogens, also called group A Streptococcus. They are contagious. They can spread through droplets when someone with the infection coughs or sneezes or through shared food or drinks.

1. DR.V.JEYANTHI KUMARI
ASSISTANT PROFESSOR OF ZOOLOGY
A.P.C.MAHALAXMI COLLEGE FOR WOMEN
THOOTHUKUDI-628002

2. INTRODUCTION
 The pathogenic Streptococcus was discovered by
T.Billroth (1874) in the tissues of patients with
erysipeias (large raised red patches of the skin)
and wound infections.
 They are Gram positive cocci arranged in chains
or pairs.
 They are important human pathogens, causing
pyogenic infections (pus forming infection).
 They are also responsible for the nonsuppurative
lesions (non pus-inflamation), acute rheumatic
fever and glomerulonephritis.

3. I.Morphology
 Streptococci are spherical in shape 0.6-1µ in
diameter, and form chains.
 They are nonmotile, do not form spores.
 Some strains are capsulated.
 The smears from culture media grown on solid
media, the Streptococci are usually present in pairs
or in short chains. The smears from broth cultures
they form long chains.

4. II
. Cultivation
 They are aerobic and facultative aerobic, and some
are anaerobic species.
 The optimal growth temperature is 370 C.
 They grow well on sugar, blood, serum and ascetic
agar and broth, when the pH of the media is 7.2-7.6.
 On solid media they produce small, translucent, grey
or grayish-white, and granular colonies with poorly
defined margins.
 Some Streptococcal strains cause haemolysis on
blood agar.

5. Long chain Streptococcus

6. III.Toxin Production
 Pathogenic Streptococci produces exotoxins with various
activities.
1.Haemolysin
 It loses its activity after 30minutes at a temperature of
550C. It disintegrates erythrocytes, produces
haemoglobinaemia and haematuria in rabbits following
intravenous injection.
2.Leukocidin
 This is destructive to leucocytes. It occurs in highly
virulent strains and is tendered harmless by a
temperature of 70oC.
3. Necrotoxin
 It produces necrosis in rabbits when injected
intracutaneously. It also causes necrosis in other tissues,
particularly in the hepatic cells.

7. 4. Lethal toxin
 It rapidly kills rabbits and white mice when injected
intravenously.
5. Erythrogenic toxin
 It produces inflammation in humans who have no
antitoxins in their blood.
 Other substances produced by the pathogenic
streptococci are harmful enzymes. They include
hyaluronidase which facilitates the spread of the
organisms throughout the tissues and organs of the
affected animal, fibrinolysin, deoxyribonuclease,
ribonuclease, protenase, amylase, lipase, and
diphosphopyridine nucleotidase.

8. IV. Antigenic Structure
 Four antigenic fractions were recovered from
Streptococci. They are
 M protein
 T protein
 C polysaccharide and
 P nucleoprotein
 ‘M’ protein is responsible for virulence, and
immunogenicity. The T proteins contain O-, K- and L-
antigens. C polysaccharide is the substance common
to whole group of haemolytic streotococci. P
nucleoproteins are common to other groups of
Streptococci.

9. V.Pathogenesis and Diseases in Man
 Streptococcus produces pyogenic infections and
spread locally, along lymphatics and through the
blood stream.
 Respiratory infection
 Skin and subcutaneous infections
 Other suppurative infections
 Nonsuppurative complications
VI.Immunity
 Immunity occurred after streptococcal infections
are of a low grade and short duration.

10. VII. Laboratory Diagnosis
 Test material is obtained from the pus of wound,
inflammatory exudates, tonsillar swabs, blood, urine
and foodstuffs.
 Tests include microscopy of the pus smear,
inoculation of test material onto blood agar plates,
isolation of the pure culture and its identification.
VIII. Treatment
 Usually penicillin is used. For penicillin resistant
strains, streptomycin, tetracycline, and erythromycin
are required. Vaccine therapy and phage therapy are
recommended in chronic conditions.

11. IX.Epideomology
 The major source of transmission is the human
upper respiratory tract-throat, nasopharynx or
nose of the patients and carriers.
 Crowding is an important factor in the
transmission of infection.
 Outbreak of infections may occur in closed
communities such as boarding schools or army
campus.

12. X.Prophylaxis
 Streptococcal infections are prevented by the
practice of general hygienic measures at
factories, children’s institutions, maternity
hospitals, and surgical departments, in food
production, agricultural work, and everyday
life.

13. Growth on blood agar (ẞ haemolysis)

14. Growth on
nutrient agar
Growth on chocolate
agar