Sputum Culture and Sensitivity

Sputum Culture and Sensitivity

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Aim of the test

An etiological diagnosis of lower respiratory tract infection by microscopic examination and culture with identification and susceptibility test of the isolated organism.

Types of specimen

Sputum, Transtracheal aspirates, translaryngeal aspiration, bronchoalveolar lavage.

Criteria of specimen rejection

Saliva (report as “Improper specimen, only saliva, please resubmit”

Infection of lower respiratory tract

The lower respiratory tract consist of the following parts: Left and right pleural cavity, bronchioles, pleural space, diaphragm, mediastinum

The common pathogens

  • Streptococcus pneumoniae
  • Haemophilus influenzae
  • Staphylococcus aureus
  • Klebsiella pneumoniae and other Enterobacteriaceae
  • Moraxella catarrhalis
  • Mycobacterium spp.
  • Fusobacterium spp.
  • Bordetella spp
  • Chlamydia pneumoniae
  • Legionella spp.

Specimen collection

Deep cough and collect sputum in a wide mouth sterile container. All expectorated sputum is contaminated to some degree with secretion of the Oropharyngeal cavity, which contains a wide variety of commensal bacteria, some of which are potential pathogens of the lower respiratory tract (S. pneumonia, Haemophilus influenzae). Since the sputum reflect the infection in the bronchi and the lung. 

Contamination Oropharyngeal secretion should be kept to a minimum. Early morning sputa is preferred because they contain pooled overnight secretion in which, pathogenic bacteria are more likely to be concentrated. The specimen should be collected in a sterile, wide-mouth container with tightly fitted screw-cap lid.
Quantity of specimen

: 3 ml

Time relapse before processing the sample : 30 min. Storage: 4 °C for not more than 2 hours

  • Media
  • Blood Agar,
  • Chocolate Agar,
  • MacConkey Agar

Culturing procedure

Inspect the sample and select bloody purulent portion and inoculate blood agar, chocolate agar, and MacConkey Agar and perform a gram stain from the specimen. Incubate the plates as indicated by the chart. Identify according to the attached charts in appendix V.

Interfering factors:

Patient on antibiotic therapy. Improper sample collection.

Result reporting: Report Gram stain finding as an initial report. Report the isolated pathogen and its sensitivity pattern as a final report.

Turnaround time: Gram stain results should be available 1 hour after specimen receipt. Isolation of a possible pathogen can be expected after 2-3 days. Negative culture will be reported out 1-2 days after the receipt of the specimen.

Additional information

During the collection of sputum, it is usually contaminated with saliva, therefore, careful collection and interpretation of results is required. Translaryngeal (transtracheal) aspiration could be requested if the patient: 1. Is debilitated and cannot spontaneously expectorate a sputum sample.

2. Routine sputum specimens have failed to recover a causative organism in cases of bacterial pneumonia.

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