COLLECTION OF SAMPLES FOR BACTERIOLOGICAL EXAMINATION

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

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

General rules should be applied to all specimens

Hands should be washed before and after the collection

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

Respiratory Tract Infection

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

1) Throat swab: URTI

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

3) Middle ear:

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

Trans-tracheal aspiration, lung biopsy, or boronchoalveolar lavage

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

Streptococci

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

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

Hemolysis on Blood agar

The most frequent etiologic agents of bacterial tonsillitis and tonsillopharyngitis are Streptococcus pyogenes strains (80- 90 %).

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.

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

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).

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

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

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

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

Scarlet fever Mostly affect children

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.

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.

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:

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