1. COLLECTION OF SAMPLES FOR BACTERIOLOGICAL EXAMINATION

2. Diagnosis of Bacterial Infection
Non-microbiological investigations
Patient
Clinical
diagnosis
Radiology
Haematology
Biochemistry
Take the correct specimen
Sample
Take the specimen aseptically in sterile container
Adequate & representative
Appropriate transport & storage of specimen
Before start of antibiotic
Label & package the specimen up correctly

3. Diagnosis of Bacterial Infection
microscopy
unstained or stained with e.g. Gram stain
culture
identification by biochemical or serological tests on pure growth from single colony
on plates or in broth
sensitivities
by disc diffusion methods
Serodiagnosis
DNA technologies

4. General rules should be applied to all specimens

5. Hands should be washed before and after the collection

6. The samples : Viral transport media. Bedside samples
Taken before the start of antimicrobial therapy.
Representative
Adequate volume.
Collected aseptically; dated, and labelled
Transported rapidly to the laboratory.
As fresh as possible.
Viral transport media.
Bedside samples

8. Respiratory Tract Infection

9. Signs & Symptoms Signs & Symptoms
Pneumonia
Pharyngitis
Infection of lungs
Signs & Symptoms
Dyspnoea
Cough
Chest pain
-Throat infection
Signs & Symptoms
sore throat
malaise

10. 1) Throat swab: URTI

12. 2)- Nasopharynx: nasopharyngeal washing or nasopharyngeal swab in meningitis and viral infection.

14. 3) Middle ear:

15. If the patient failed to expectorate
4) Lower respiratory:
Early morning sputum.
If the patient failed to expectorate

16. Trans-tracheal aspiration, lung biopsy, or boronchoalveolar lavage

17. Aspiration of gastric contents that contain swallowed sputum, in children.

18. Streptococci

19. General characters facultative anaerobe Gram-positive chains or pairs
catalase negative

20. Classification of Streptococci Based on Hemolysis on Blood Agar
Hemolysis on BA
-hemolysis
Partial hemolysis
Green discoloration around the colonies
e.g. non-groupable streptococci (S. pneumoniae & S. viridans)
-hemolysis
Complete hemolysis
Clear zone of hemolysis around the colonies
e.g. Group A & B (S. pyogenes & S. agalactiae)
-hemolysis
No lysis
e.g. Group D (Enterococcus spp)
Streptococci
-hemolysis
-hemolysis
-hemolysis

21. Hemolysis on Blood agar

22. The most frequent etiologic agents of bacterial tonsillitis and tonsillopharyngitis are Streptococcus pyogenes strains ( %).

24. differs according to the clinical presentation.
Laboratory Diagnosis Diseases Caused by S. pyogenes:
Samples:
differs according to the clinical presentation.
Direct film stained with Gram stain: Gram positive cocci arranged in long chains, non spore forming, non motile and have a capsule of hyaluronic acid.

27. Culture:
Culture characters: facultative anaerobes, can grow in normal atmospheric CO2 concentration, (10% CO2 enhance growth); optimum temp. 37C.
Ordinary media: no growth.
On blood agar: S. pyogenes cause  haemolysis with small (pin point) and translucent colonies

29. Film stained by gram to show the morphology.
Growth can be identified systemically by:
Film stained by gram to show the morphology.
Catalase test: negative (differentiate them from staphylococci).

30. Catalase Test Positive test: rapid appearance of gas bubbles.
Catalase +ve
Catalase -ve
Staphylococci
Streptococci

31. Bacitracin (0.04 g) sensitivity: sensitive (differentiate them from other beta hemolytic streptococci which are bacitracin resistant).

33. Specific identification of S
Specific identification of S. pyogens can be done by reaction with specific antibodies.

34. Diagnosis of rheumatic fever
Clinical picture & history of preceding streptoccal infections.
Laboratory diagnosis by:
a-Non specific tests as C- reactive protein & high ESR .
b-Specific tests : by detection of an increase in antibody titer to at least one of the streptococcal antigens including antistreptolysin O (ASO) which is most widely used ,anti-DNase , antihyaluronidase& antistreptokinase

35. Scarlet fever
Mostly affect children

36. Diagnosis of Scarlet Fever:
a) Specimen: throat swab, examined as mentioned before.
b) Schultz Charlton reaction
Principle: it is a neutralization test in vivo.
Method:
Intradermal injection of the anti–erythrogenic toxin in the erythematous area of skin rash will lead to fading of the rash within 6-12 hours in positive cases.

37. c) Dick test:
Uses:
The test is used to assess the susceptibility of individuals to scarlet fever.
Principle:
Erythrogenic toxin is irritating and causes local reaction when injected intradermal unless it is neutralized by specific antitoxin.
Method:
0.1 ml of toxin is injected intradermal in one forearm (test) and the same amount of heated toxin (detoxified) is injected in the other forearm (control) the test is read within 4-7 days.

38. Positive test (susceptible) redness and swelling in the test arm that reaches maximum after 4-7 days and disappear gradually. No reaction in the control arm.
Negative test (immune) No reaction on both arms.
Pseudo- reaction (hypersensitivity): reaction that appears and disappears in both arms at the same time.
Combined reaction: reaction in both but the reaction in the control arm disappear rapidly more than the tested arm.
Interpretation:

40. Thank You