Study of detailed conditions in DNA probe test by use of Gen-Probe Rapid Diagnostic System for identification of Mycobacterium avium complex and Mycobacterium tuberculosis complex

In order to improve feasibility of technical procedures in Gen Probe Rapid Diagnostic System (Gen Probe Inc., San Diego, CA, U.S.A.) for identification of Mycobacterium avium complex (MAC) and M. tuberculosis complex (MTC), we studied several test conditions in the DNA probe testing, such as stability of test bacterial suspension, optimal duration of bacterial cultivation, the number of organisms in test bacterial suspension required for accurate determination, and so on. With respect to concentration of organisms (MAC and MTC) in test bacterial suspension (0.1ml), we found that 5-fold dilution as well as 5-fold condensation of the standard bacterial suspension (McFarland No.1) gave substantially the same result as in the case where bacterial suspension at the standard concentration was used. This indicates that the test bacterial suspensions (0.1ml) containing either 1.5 X 10(7)-5 X 10(8) of MAC or 3 X 10(5)-8 X 10(6) of MTC are available for the DNA probe testing. Test bacterial suspension at McFarland No.1 prepared from fresh cultures (3-4 week-old) could be stored either at -80, -20 or 4 degrees C at least for 17 weeks without significant loss of reactivity to M. avium, M. intracellulare and MTC DNA probes. In this case, stability of DNA probe-reactivity was preserved in the following order: MTC, M. avium and M. intracellulare. Concerning the age of bacterial cultures, at least 16-week-old cultures of MAC and MTC after initial appearance of cell growth on 1% Ogawa's egg media were sufficiently reactive to either MAC or MTC DNA probe. In this case, MTC showed most stable reactivity during the course of long-term cultivation.(ABSTRACT TRUNCATED AT 250 WORDS)