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Chapter 7.4 : Liquid Media for Isolation
In the BACTEC 460TB radiometric system (Becton Dickinson Diagnostic Systems, Sparks, Md.), growth medium for culturing mycobacteria is supplemented with a substrate labeled with radioactive carbon (14C). This substrate is utilized by mycobacteria, and during metabolism, carbon dioxide (14C2) is produced from the substrate. The 14C2 is detected quantitatively by counting the radioactivity with a BACTEC 460 instrument. The rate and amount of 14C2 produced are directly proportional to the rate and amount of growth occurring in the medium. This principle is applied for isolation of mycobacteria from clinical specimens, differentiation of the Mycobacterium tuberculosis complex from other mycobacteria, and antimicrobial susceptibility testing.