[Usefulness of the microcolorimetric method of XTT reduction for evaluation of intracellular killing of pathogens].

The aim of this study was to evaluate a XTT assay in testing the killing activity of mouse phagocytes in vitro. Live microorganisms converted XTT to water soluble orange formazan in the presence of CQ. Absorption of formazan measured at 492 nm was directly related to the number of viable cells. The percentage of staphylococci killed by granulocytes and macrophages was 10-40% (1 h- and 2 h-respectively), in the cultures containing 10 bacteria/phagocyte. Killing of Candida albicans (1-3 blastospors/phagocyte) was seen after 2 h of incubation. The percentage of Listeria and Mycobacterium killed by phagocytes depended on pathogenicity of the tested strains. The bactericidal activity of phagocytes estimated in the XTT assay and by the CFU method was quite similar.