A RAPID COLORIMETRIC ASSAY FOR EVALUATING LEGIONELLA-PNEUMOPHILA GROWTH IN MACROPHAGES IN-VITRO

A rapid colorimetric technique for in vitro quantitation of Legionella pneumophila intracellular proliferation in macrophages is described. The assay is based on the electron transport activity of metabolically active L. pneumophila. The yellow tetrazolium salt (4,5-dimethylthiaz ol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) is cleaved by the mitoc hondrial activity of viable L. pneumophila, forming a dark formazan de rivative with an absorption spectrum different from that of the native compound. The MTT method for measuring intracellular growth of L. pne umophila closely correlated with the CFU assay. The ability of macroph ages from the A/J mouse strain to support intracellular growth of L. p neumophila and the ability of desferrioxamine to restrict L. pneumophi la intracellular proliferation were confirmed by both methods. The MTT assay offers the advantages of rapidity, simplicity, and cost efficie ncy over the CFU assay, since it can be performed in the same flat-bot tom microtiter plate with measurement in an enzyme-linked immunosorben t assay reader, allowing efficient processing of large numbers of samp les.