Decontamination of Contaminated MGIT Culture

Usually, more than one specimen is collected from a patient. Therefore, it is not necessary to salvage a contaminated specimen if other specimens from the same patient are positive and not contaminated. However, if it is critical to have the results of a particular specimen that was contaminated, the broth may be reprocessed.

The steps involved are as follows:

1.  The entire contaminated MGIT broth should be transferred into a 50 ml centrifuge tube.

2.   An equal quantity of sterile 4% sterile NaOH solution. 

3. This should be mixed well and allowed to stand for 15-20 minutes while mixing the tube by inverting it periodically.

4.   Phosphate buffer of pH 6.8 should be added after 15-20 mins up to the 40 ml mark on the centrifuge tube and mixed well by inverting the tube. Phosphate buffer of pH 6.8 should be added after 15-20 mins up to the 40 ml mark on the centrifuge tube and mixed well by inverting the tube. 

5. Centrifugation should be done at 3000g for 15-20 minutes.

6.  The supernatant fluid is poured off.

7.   The sediment is resuspended in 0.5ml phosphate buffer (6.8 pH) and mixed well. 

8.  0.5 ml of this is inoculated into a fresh MGIT tube supplemented with the MGIT growth supplement/PANTA. 

9. The inoculated tubes are left at room temperature for 30 minutes and then placed in the instrument. This is followed up for observation of growth.

10. If no growth is observed, Autoclave all inoculated MGIT tubes before disposal.

    Resource

Mycobacteriology Laboratory Manual 

Assessment