This document discusses Streptococcus pyogenes (Group A Streptococcus) and Streptococcus viridans. It describes their morphology, culture characteristics, and diseases they cause including pharyngitis, impetigo, scarlet fever, and subacute bacterial endocarditis. The document outlines methods for diagnosing streptococcal infections through gram stains, cultures on blood agar with bacitracin discs, and serological tests. It also describes blood culture techniques used to diagnose diseases associated with bacteremia.

1. By
Eman A. Abd
Alrahman 1

2. STREPTOCOCCI
 Streptococci are gram
positive cocci.
 Arranged in chains or
pairs.
 All streptococci are
catalase negative.
 Grow on enriched media.
 Facultative anaerobes.
2

3. Streptococcal classification
3

4. 4

5. Infections caused by Streptococcus pyogenes
Pyogenic
infections
Invasive
infections
Toxogenic
infections
Post streptococcal
diseases
Pharyngitis
Impetigo
•Erysipelas
• Cellulitis
• Puerperal
sepsis
• Acute bacterial
endocarditis
•Streptococcus
toxic shock
syndrome
• Scarlet fever
•AGN
• ARF
5

6. Diseases caused by Str. pyogenes
I.pharyngitis
.
.
6

7. •A local infection of the
skin characterized by
formation of blisters
which break leaving a
denuded surface covered
with pus or crusts.
•May be followed by acute
glomerulonephritis
Impetigo
7

8. II-
8

9. 9

10. 10

11. III-Post streptococcal diseases
11

12. •Specimens: Swabs from throat or other lesions, pus,
or blood in case of bacteraemia or septicaemia.
Diagnosis of streptococcal infections
12

13. Diagnosis of Streptococcal Diseases:
•Direct smears stained by gram show gram
positive cocci in chains.
Gram stained film of
Streptococci in culture Gram stained film of
Streptococci in pus
13

14. Cultures :
Done on blood agar incubated at 37°C. Colonies
producing complete haemolysis,.
 Catalase negative .
B. hemolysis on blood
agar 14

15. Bacitracin sensitivity test is done by placing a
bacitracin disc on the inoculum of the organism on
blood agar. A zone of inhibition around the disc is
observed in case of group A streptococci
15

16. Blood cultures are done for infections associated with
bacteraemia or septicaemia e.g. bacterial endocarditis
and puerperal sepsis..
Blood culture bottle
16

17. Lab diagnosis of post-streptococcal diseases:
Recent history of Str. pyogenes infection.
 Serologic tests.
1)Antistreptolysin O: more than 200 units
2)Anti-DNase B antibodies are high (80 units or more) in
group A streptococcal skin infections
3) Other less specific laboratory tests include;
• High erythrocyte sedimentation rate (ESR).
• Positive C-reactive protein (CRP).
17

18. 18
STREPTOCOCCUS VIRIDANS
Morphology: Gram positive
cocci arranged in short chains
or in pairs.
.
Culture Characters: Its colonies
give partial haemolysis (greenish
discolouration) on blood agar

19. 19
Diseases caused by S.viridans:
•Dental caries.
•Subacute bacterial endocarditis.
Blood culture is done for the diagnosis of
subacute bacterial endocarditis
All diseases where bacteraemia occur as in typhoid
fever, brucellosis, puerperal sepsis, meningococcal
meningitis, etc.
- Also, in septicemia due to any organism.
‫مهم‬

20. 20
Blood culture technique: -
•A strict aseptic technique should be used.
•5 - 10 ml of blood are withdrawn with a sterile syringe after
thorough sterilization of the puncture area to avoid contamination
of the specimen with skin commensals S. epidermidis.
1) 5-10ml
blood

21. 21
•The blood is added to 50 ml broth in blood culture bottles,
which are incubated at 37°C .
• Subcultures are made every day by withdrawing small amount
of blood broth mixture and plating it out on blood agar.
• The colonies that arise are identified and their antibiotic
sensitivity tested.
• If results of subculture are negative for 7 successive days,
discard the blood culture.
The excess volume of broth has the following advantages:
•It provides good nutrition for multiplication of the organism
which is usually present in small numbers.
•It dilutes out any antibiotic or other anti bacterial substances
in the serum.