Transcript Sputum Culture and Sensitivity

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 .
Pathogen and commensals
Specimen collection
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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
• 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 screwcap.
Culturing procedure
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.
Pathogen and commensals
Specimen collection
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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.
Storage: Maintain specimen at room temperature
Specimen processing
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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.
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.