Examination of Mycobacterium Tuberculosis

Examination of Mycobacterium Tuberculosis

The smear from the sputum can be make for demonstration of the present acid bacilli, but cannot be used for examination of turbercle bacilli.

Petroff’s Method for Examination Of M.T

mix the sputum with sodium hydroxide in a sterile wide mouth container, the volume of the sputum should be 3 or 4 times of sodium hydroxide.

After the mixing then shake the solution vigorously with shaking machine for 20 minutes that is (house in an exhaust cabinet). Then centrifuge the solution with centrifuge for 15minutes at 3000rpm. Discard the supernatant into a clean sterile container suspend the supernatant into a 25ml of sterile glass distilled water made up of 100ui/ml  of penicillin.

Spin the solution again for 15 minutes at 3000rpm, discard the supernatant, make a film from the deposit. Stain with Ziehl-Neelsen method and examine. From the deposit inoculate two lewestein-Jensen slope, incubate at 37ºC in a flat position for 24 hours. The fluid should be allowed to spread gradually on the surface of the medium. Then upright the plate and incubate at 37ºC for 8 weeks the culture should be check weekly.

Swabs: these are the best collected into a transport medium in other to preserved the life of delicate organism. several of these are commercially available which they are incorporate into the swab stick. If swabs is taken, it is recommended to be culture immediately on the arrival of the swabs to the laboratory. Before making a film with the swabs it is recommended that inoculation should first attended to before film preparation. even after the examination of the film, it is necessary that you should not relays on the film result only. The important used is not to include the infection of vicents, that is present of spirochete and fusiform bacilli from throat swabs. But normal flora may include diphtheria, Neisseria, viridans and non-hemolytic streptococci.

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Throat Swabs: this is a swabs is culture in the following way in other to demonstrate present microorganism in the patient.


Inoculate specific amount of the sample into a plate agar and incubate  aerobically and anaerobically specifically 35ºC. But if diphtheria is the suspecting microorganism, the sample should be inoculated on loeffers serum slopes and blood tellurite and incubate at 35ºC. on the next day, examine, report any growth of colonies found.

Postnasal and Personal swabs

As the name implied, is a swabs stick deign personally usually for swabbing of pharyngeal sample for laboratory investigation. The swab stick is usually prepared personal instead of using a commercially available once. In respect to this swab stick, there are still commercially available one which can be used if the laboratory personal was unable to produce its own.

Either commercially or personally prepared swab stick, it must be made up of the following; Lengths 150mm, and must be made up of nichrome or SWG copper wire. They are bent in a slight of 25mm from the end. The sterilization of the swabs take place in a hot air.

Before the sterilization proceed the swabs is place inside a tube with approximate length and width of 125mm x 12mm. they are mostly used for case of patient with meningococcal carriers and whooping cough.

Culture Method

After collection of the specimen, incase of suspicious of whooping cough inoculate the swab sample on Bordet-Gengour plate incorporated with 0.25µ/ml of penicillin  or Laceys DPF plates and incubate for 2-4 days at 35ºC

But if meningococcal is suspected, then inoculate the swabs sample on chocolate agar, then incubate it in the present of 10% CO2 for 1-2 days at 35ºC

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