Troubleshooting LC Growth Recovery

If there is an overall decrease in the culture positivity rate, the following parameters need to be investigated:

A. Incubation:

The majority of mycobacterial species grow well at 37°C ± 1ºC. They may grow slowly or may not grow if the temperature drops below 35°C. If an incubator is used, confirm that the incubator's temperature is 37°C ± 1°C by placing a calibrated thermometer in various locations throughout the incubator or instrument drawers. Monitor the readings several times each day until heating stability is determined. Check the temperature of the MGIT 960 by retrieving the information from the instrument. 

 B. Decontamination Procedure:

1. Confirm that the purity and concentration of all the reagents used in the digestion/ decontamination procedure are satisfactory.

2. Use distilled/ deionized water only for the preparation of reagents.

3. It is better to start with freshly prepared reagents.

4. A high pH of the specimen inoculated into the MGlT medium may influence the performance of MGlT adversely.

5. Do not expose the specimen to the decontamination reagent for longer than the recommended time.

6. Check if MGlT tubes are positive by visual growth but negative by fluorescence.

C. Centrifugation:

1.  Relative Centrifugal Force (RCF) should be 3,000-5,000 x g. Make sure the centrifuge is giving the required RCF.

2. The generation of heat during centrifugation also lowers the recovery due to higher temperature. Avoid the generation of excessive heat by using a refrigerated centrifuge.

D. Use of PANTA:

Check that PANTA is reconstituted with the proper volume.

Resource

Mycobacteriology Laboratory Manual 

Assessment