Sputum Culture and Throat Swab

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  Patient preparing Patient is asked to wash oral cavity by gargling 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, Haemophilus influenzae).  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.

 Who will collect the specimen The patient  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.

Throat Swab

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  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.

 The posterior pharynx should be firmly rubbed with the swab.  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  Media Blood Agar Columbia CNA Selective media which selects for Gram-positive bacteria. It contains two antibiotics, colistin and naladixic acid  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.

Additional information  Rheumatic fever remains a concern all over the world and serious complications including sepsis, soft tissue invasion, and toxic shock-like syndrome have been reported to be increasing in frequency; therefore, timely diagnosis and early institution of appropriate therapy remains important.

 Timely therapy may reduce the acute symptoms and overall duration of streptococcal pharyngitis.  The sequelae of poststreptococcal glomerulonephritis and rheumatic fever are diminished by early therapy.

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