Detection of Mycobacterium tuberculosis in mixed broth cultures using DNA probes

OBJECTIVE: To investigate the ability of a commercial acridinium ester-labeled DNA probe (AccuProbe, Gen-Probe Inc., USA) to detect the presence of Mycobacterium tuberculosis complex in a mixed culture with Mycobacterium avium complex. METHODS: The density of organisms required to produce a positive result for Mycobacterium tuberculosis complex alone in broth culture was compared with the density required to produce a positive result in the presence of Mycobacterium avium complex. RESULTS: A threshold density of 1.5 x 106 CFU/mL was required for detection of Mycobacterium tuberculosis and this threshold remained unaltered in the presence of Mycobacterium avium complex. The presence of Mycobacterium avium complex had no effect on detection of Mycobacterium tuberculosis in a mixed broth culture incubated and probed over a 21-day period. CONCLUSIONS: The findings of the study suggest that the presence of Mycobacterium avium complex has no effect on the detection of Mycobacterium tuberculosis and that the Accuprobe test is potentially capable of detecting a dual infection with organisms of both complexes.