A rapid [3H]glycerol radioassay for determination of monocyte-mediated growth inhibition of Mycobacterium avium.

[3H]glycerol was used to radiolabel Mycobacterium avium (MA) bacteria after interaction with human monocytes in a rapid in vitro assay for determination of the growth inhibition of the mycobacteria by monocytes. Monocytes and MA were co-cultured in 96-well microtiter plates for 1-5 days, and [3H]glycerol was added for an additional 3 days of incubation to radiolabel residual bacteria. The results indicate that monocytes inhibited mycobacterial growth within 24 h of co-culture, an activity which increased during incubation until optimal growth inhibition was noted by 3-4 days. A comparison with conventional plate counting methodology demonstrated similar responses between the two assays except that the conventional assay required 2-3 weeks of culture before visible MA colonies could be detected and enumerated. Thus, the development of a rapid radiolabel assay to quantitate the interaction between monocytes and MA will facilitate the investigation of normal host responses to this opportunistic pathogen.