Troubleshooting LC Detection Time

Detection time can range from 24 hours to six weeks for MGIT and 8 weeks for LJ medium. If the average detection time is significantly longer, these instructions need to be followed:

Digestion/decontamination procedure:

1. Decrease the NaOH concentration and/or time of exposure to NaOH. Higher concentrations of NaOH or longer exposure time will prolong the detection time of mycobacteria.

2. A high pH of the final inoculum will prolong the detection time.

3. Check if the incubation temperature is within specifications. Lower temperatures would delay detection.

4.  In a few instances, too high a concentration of PANTA may delay the detection of certain strains of NTM, especially if the starting number is low.

Procedures Check:

1. Water used to prepare reagents should be pure (distilled/deionized). 

2. All the reagents used should be sterile. 

3. All pipettes and tubes should be sterile.

4. All inoculations should be made in the biological safety hood.

5. Growth Supplement/PANTA mixture should be added to MGIT tubes just before inoculation.

6. The addition of MGlT OADC or MGIT Growth Supplement/PANTA must be done inside a biological cabinet. Leave the tube open for as little time as possible. Leaving the tube open, especially on an open bench top, would increase the contamination rate.

   Resource

Mycobacteriology Laboratory Manual 

Assessment