Culture & Sensitivity, Aerobic bacteria Sputum (Manual method)

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Detect aerobic bacterial infections of the lower respiratory tract by analyzing a sputum sample (phlegm coughed up from the lungs)

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Culture & Sensitivity, Aerobic bacteria Sputum (Manual method)

Why is it done?
- Identifies aerobic bacteria in respiratory secretions (sputum) that may be causing lower respiratory tract infections
- Determines specific bacterial pathogens in patients with suspected pneumonia, bronchitis, or other pulmonary infections
- Performs antibiotic susceptibility testing to guide targeted antimicrobial therapy
- Commonly ordered for patients with productive cough, fever, and clinical signs of lower respiratory tract infection
- Used to monitor treatment response in hospitalized patients or those with recurrent infections
- Essential in immunocompromised patients, those with chronic lung disease, or suspected nosocomial infections
Normal Range
- Normal Result: No growth of pathogenic aerobic bacteria (sterile culture)
- Expected Range: 0 colony-forming units per milliliter (CFU/mL) of pathogenic organisms; normal respiratory flora may be present
- Units of Measurement: CFU/mL; organism identification by microscopy and biochemical testing; antibiotic susceptibility reported as Sensitive (S), Intermediate (I), or Resistant (R)
- Positive Result: Growth of pathogenic aerobic bacteria indicates active respiratory infection
- Interpretation: Absence of growth suggests either no bacterial infection, inadequate specimen, or improper collection; presence of growth with >100,000 CFU/mL generally considered clinically significant
Interpretation
- No Growth (Sterile): Indicates no bacterial pathogen identified; may reflect adequate recovery in viral infections, early stage infection, or appropriate antibiotic therapy already in effect
- Single Pathogen Identified: Suggests community-acquired pneumonia or acute infection; common organisms include Streptococcus pneumoniae, Haemophilus influenzae, Staphylococcus aureus, or Gram-negative bacilli
- Multiple Organisms: May indicate mixed infection, contamination from oral flora, or inadequate specimen handling; requires clinical correlation
- Antibiotic Sensitivity - Sensitive (S): Organism is likely to respond to standard doses of the antibiotic; indicates appropriate drug selection for treatment
- Antibiotic Sensitivity - Intermediate (I): Organism may respond to higher doses or prolonged therapy; clinical response dependent on drug concentration at infection site
- Antibiotic Sensitivity - Resistant (R): Organism unlikely to respond to standard therapy; alternative antibiotics must be considered
- Factors Affecting Results: Patient already on antibiotics (may reduce bacterial growth), specimen contamination with saliva or oral flora, improper collection timing, delayed transport to laboratory, or mixed infections may complicate interpretation
- Clinical Significance of Patterns: Quantitative results (CFU/mL) help differentiate true pathogens from colonization; >100,000 CFU/mL generally indicates infection; lower counts may represent colonization or contamination; Gram stain quality indicator (squamous epithelial cells vs. white blood cells) helps assess specimen adequacy
Associated Organs
- Primary Organ System: Lower respiratory tract including lungs, bronchi, bronchioles, and alveoli
- Associated Diseases/Conditions: Community-acquired pneumonia (CAP), hospital-acquired pneumonia (HAP), ventilator-associated pneumonia (VAP), acute exacerbation of chronic bronchitis, cystic fibrosis with respiratory infection, bronchiectasis
- Common Bacterial Pathogens Detected: Streptococcus pneumoniae, Haemophilus influenzae, Staphylococcus aureus (including MRSA), Pseudomonas aeruginosa, Escherichia coli, Klebsiella pneumoniae, Legionella species, Moraxella catarrhalis
- Potential Complications of Abnormal Results: Sepsis and bacteremia (bacteria entering bloodstream), respiratory failure requiring mechanical ventilation, abscess formation, pleural effusion or empyema, acute respiratory distress syndrome (ARDS), delayed treatment with inadequate antibiotics leading to worsening infection
- Risk Groups: Elderly patients, immunocompromised individuals (HIV/AIDS, chemotherapy patients), those with chronic lung disease (COPD, asthma), cardiac disease, diabetes, renal failure, alcoholism, smokers, hospitalized patients, and those on prolonged antibiotic therapy
Follow-up Tests
- Based on Positive Culture: Blood cultures to assess for bacteremia/sepsis; complete blood count (CBC) to evaluate white blood cell response; comprehensive metabolic panel to assess organ function; chest X-ray to visualize extent of pneumonia; procalcitonin or C-reactive protein (CRP) to monitor infection severity
- Extended/Special Testing: Culture for anaerobic bacteria if aspiration pneumonia suspected; fungal culture if immunocompromised; acid-fast bacilli (AFB) stain and culture for TB if indicated; viral testing (influenza, RSV, COVID-19) to evaluate concurrent infections; extended antibiotic resistance panel for resistant organisms
- Repeat Culture Indications: Persistent symptoms after 48-72 hours of appropriate therapy; clinical deterioration on current antibiotics; suspected treatment failure; hospital-acquired infection monitoring; changes in clinical status
- Monitoring Frequency: Initial culture obtained at diagnosis; repeat cultures typically performed if clinical response inadequate at 48-72 hours; for chronic conditions (cystic fibrosis, bronchiectasis), cultures may be obtained quarterly or semi-annually; hospitalized patients with VAP may have serial cultures per protocol
- Complementary Tests: Sputum Gram stain for organism morphology; molecular testing for rapid identification (PCR for specific pathogens); bronchoalveolar lavage (BAL) culture if sputum inadequate; pleural fluid culture if effusion present; imaging studies (CT chest) if diagnosis unclear or complications suspected
Fasting Required?
- Fasting Required: No
- Pre-Test Preparation: No food, fluid, or medication restrictions apply; patient may eat and drink normally before collection
- Specimen Collection Instructions: Patient should rinse mouth with water (not mouthwash) before collection to reduce oral contamination; collect sputum by deep cough (not saliva); use sterile container provided by laboratory; collect early morning specimen preferably as it contains overnight secretions; minimum volume 1-2 mL of purulent material
- Medications to Continue: All regular medications should be taken as prescribed unless specifically instructed otherwise by physician; antibiotics already started may reduce bacterial yield but should be continued
- Important Patient Instructions: Avoid contamination with saliva - patient must cough deeply to produce sputum from lower respiratory tract, not upper respiratory secretions; use sterile container only; label specimen immediately with patient identifiers; transport to laboratory within 1 hour if possible (optimal within 30 minutes for best recovery); refrigerate if transport delayed to preserve organism viability
- Special Considerations: If patient unable to produce sputum spontaneously, physician may order inhalation of hypertonic saline to induce sputum production or bronchoscopy with bronchoalveolar lavage for specimen collection; never use 24-hour collections as organisms may not survive this duration

How our test process works!