Quality Control of MGIT 960 Tubes

MGIT 960 media quality control (QC) is to be done upon receipt of a new shipment or lot number. This includes checking the media visually and by growing control strains of Mycobacterium. Steps include:

• Visually check the tube for​:
  • Turbidity/contamination ​
  • Expiry date​
  • Breakage ​
  • Transport condition​

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• Control organisms prepared in Middlebrook 7H9 Broth should be used for QC testing as per the procedure shown in the figure below. It is important to test all three organisms, as each have different requirements for growth, and each will demonstrate a different time to detection.  A good quality control program ensures that the media supports the growth of a variety of organisms, not just one organism. ​

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Figure: Control strains used for quality control of MGIT tubes

• Quality control testing should be performed in a biosafety cabinet 
• Subculture the quality control strains on Lowenstein-Jensen (LJ) slants and use pure and fresh growth to prepare a uniform suspension of 0.5 McFarland turbidity ​​
• Dilution of culture suspension using sterile saline or distilled water​, accordingly:
  • M. tuberculosis - 1:500
  • M. fortuitum - 1:5000
  • M. kansasii - 1:50000​
• Inoculate 0.5 ml of respective dilutions of culture suspension into two labeled MGIT tubes and further incubate the tubes into MGIT 960 system ​​
• ​The expected results are: ​
  • M. tuberculosis: Positive in 6 to 10 days
  • M. kansasii: Positive in 7 to 11 days
  • M. fortuitum: Positive in 1 to 3 days

Resources

• MGIT procedure manual

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