NATIONAL HEALTH LABORATORY SERVICE: ACUTE BACTERIAL PNEUMONIA - II

NATIONAL HEALTH LABORATORY SERVICE: ACUTE BACTERIAL PNEUMONIA - II

Overview

  • Presenter: Dr. P Bhola

  • Institution: University of KwaZulu-Natal, Department of Medical Microbiology

Common Organisms Causing Acute Bacterial Pneumonia

  • Streptococcus pneumoniae

  • Haemophilus influenzae

  • Moraxella catarrhalis

  • Staphylococcus aureus

  • Pseudomonas aeruginosa

Specimen Types for Lower Respiratory Tract Infections

  • Expectorated Sputum

  • Induced Sputum

  • Endotracheal Aspirate

  • Broncho-Alveolar Lavage

  • Other:

    • Blood cultures (reference: Boyles et al., South Africa CAP guidelines)

    • Urine (for Legionella urinary antigen testing)

Collection Guidelines

1. Expectorated Sputum

  • Patient must:

    • Rinse mouth with water prior to collection.

    • Cough deeply to produce sputum.

  • Collect sputum in a sterile container (dry, screw-capped, e.g., a urine container).

  • Consultation with physiotherapists may be needed for patients who have difficulty producing sputum.

  • Important Notice: Position the collector behind patient to avoid aerosols. Do not collect saliva. Send specimens before starting antibiotics.

2. Induced Sputum

  • Patient must:

    • Brush buccal mucosa (without toothpaste).

    • Rinse mouth thoroughly with water.

  • Use a nebulizer to have the patient inhale approximately 20–30 mL of 3–10% sterile saline.

3. Endotracheal Aspirate

  • Aspirate specimen into a sterile sputum trap.

  • Note that tracheostomy leads to colonization within 24 hours of tube insertion. Correlate microbiology results with clinical findings.

4. Broncho-Alveolar Lavage Specimen

  • Follow departmental protocols; requires experience with bronchoscopy.

  • Use a sterile, screw-capped container with a small amount of sterile saline. Do not use formalin.

Laboratory Diagnosis

Basic Steps

  • Microscopy: Examination of the specimen using light microscopy.

  • Culture: Isolation of organisms in a laboratory setting.

  • Susceptibility Testing: Identifying bacterial resistance to antibiotics.

  • Molecular Testing: Advanced techniques for organism identification.

  • Serology: Detection of antibodies in patient serum.

1. Streptococcus pneumoniae

Laboratory Diagnosis

  • Gram Stain Findings:

    • Typically displays as gram-positive cocci in pairs (diplococci).

    • Ends of cells exhibit a pointed, oval or lancet shape.

    • Cocci may occur in singles, pairs, or short chains.

    • Over time, as cultures age, Gram stain reaction may become variable.

    • Capsules can be demonstrated using a capsule stain.

  • Culture:

    • Nutritional requirements are complex.

    • Suitable media: Brain-heart infusion agar, trypticase soy agar with 5% sheep RBCs, or chocolate agar.

    • The organism can utilize a wide range of carbohydrates; displaying α-hemolytic colonies.

    • Young colonies are glistening and mucoid; older colonies exhibit autolytic changes, resulting in ‘draftsmen colonies.’

  • Challenges in Diagnosis:

    • The tendency of Streptococcus pneumoniae to undergo autolysis complicates isolate preservation.

    • Distinguishing S. pneumoniae from viridans streptococci is critically important.

    • Methods include:

      • Optochin susceptibility testing.

      • Bile solubility tests.

      • Quellung reaction (capsule swelling).

Susceptibility Testing

  • Employ multiple methods:

    • Disc Diffusion: Utilize appropriate antibiotics.

    • Perform Minimum Inhibitory Concentration (MIC) tests when necessary.

Treatment

  • Drug of Choice (DOC): Penicillin.

  • Alternatives include Cephalosporins and Macrolides (in case of penicillin allergy).

2. Haemophilus influenzae

General Characteristics

  • Among the smallest of bacteria, often referred to as coccobacilli due to their rounded ends.

  • Possesses a cell wall similar to other Gram-negative bacteria.

  • H. influenzae may have a polysaccharide capsule, while other species might be non-encapsulated.

  • Characteristically:

    • Nonmotile,

    • Facultatively anaerobic,

    • Ferments carbohydrates,

    • Generally oxidase and catalase positive,

    • Reduces nitrates to nitrites, and is an obligate parasite on mucous membranes.

Growth Factor Requirements

  • The genus name