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 (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 screw- cap.

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 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 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.