Sputum Culture and Sensitivity

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Sputum Culture
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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 .

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Pathogen and commensals
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Specimen collection

• Patient preparing patient is asked to wash oral
  cavity by gargling (normal saline) with water 3-4
  times.
• 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, H. influenzae).
• Contamination oropharyngeal secretion should be
  kept to a minimum

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• Early morning sputum 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.

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Culturing procedure
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Throat Swab
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Aim of the test

• Isolate and identify group A beta-hemolytic
  streptococci establish the diagnosis of strep
  throat infection.
• Types of specimen
• Material from posterior pharynx, tonsils, or
  other inflamed area.

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Pathogen and commensals
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Specimen collection

• Both tonsillar pillars and the oropharynx should
  be swabbed.
• Do not allow the to touch the tongue.
• The patient is instructed to tilt his/her head
  back and breath deeply.
• The tongue is gently depressed with a tongue
  blade to visualize the tonsillar fossa and
  posterior pharynx.
• The swab is extended between the tonsillar
  pillars and behind the uvula, care should b taken
  not to touch the lateral walls of the buccal
  cavity or the tongue to minimize contamination
  with commensal bacteria.
• After collection, the swab should be placed
  immediately into sterile tube or other suitable
  container for transport to the laboratory.

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Storage Maintain specimen at room temperature
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Specimen processing

• Media
• Blood Agar
• Columbia CNA
• Selective media which selects for Gram-positive
  bacteria.
• It contains two antibiotics, colistin and
  naladixic acid which inhibit the growth of
  gram-negative bacteria, thus selecting for
  Gram-positive organisms
• Culturing procedure
• Streak the swab across blood agar plate and
  Columbia CNA to make a line that divide the plate
  into two halves, and using a sterile loop,
  streak by crossing the line to produce isolated
  colonies. Make few stabs in the agar.
• Do a gram stain from the swab noting the
  predominant organism.

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Turn around 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.

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