Culture

The processed specimen, used for culture, is inoculated on media. At least two solid media types should be used, including one serum- and one egg-based. Typical solid media can include:

• Middlebrook 7H10 (agar base with 2% glycerol, serum-based medium)
• Middlebrook or Mitchison 7H11 (selective agar base with antibiotics)
• Lowenstein-Jensen (L-J), Gruft (selective, egg-based medium with antibiotics)
• Mycobactosel™ agar (L-J medium with antibiotics, BBL Microbiology Systems, Cockeysville, MD)

Broth media can recover more rapidly, approximately 10 days versus 17 days or longer with conventional solid media. Typical broth agar can include 7H9 with TWEEN^® 80 added as a surfactant to disperse clumps of AFB for bottles and tubes. This broth media is used in:²⁶

• Manual methods
• Semi-automated radiometric methods: BACTEC™ 460 (Becton-Dickinson, Sparks, MD)
• Automated systems:
• BACTEC™ 9000 MB (Becton-Dickinson)
• BACTEC™ MGIT™ 960 (Becton-Dickinson)
• ESP^® Culture System II (Trek Diagnostic Systems, Cleveland, OH)
  
• VersaTREK^® (Trek Diagnostic Systems, Cleveland, OH)
• MB/BacT ALERT^® 3D system (bioMérieux, France)

The BACTEC™ MGIT™ 960 and the BACTEC™ 460 systems range in sensitivity from 81.5% to 85.8%, and their specificity to detect mycobacteria is 99.6% and 99.9%, respectively. Sensitivity is increased to 87.7% and 89.7% when solid media culture is combined with automated testing.

Detection of mycobacteria by automated systems monitored continuously is state-of-the-art for culturing and rapidly recovering mycobacteria (10–14 days compared to 18–24 days on egg-based media).