Early detection of Chlamydia trachomatis using fluorescent , DNA binding dyes

HeLa 229 cells were infected with genital tract strains of Chlamydia trachomatis. After incubation for varying times the infected cells were fixed and stained with the fluorescent DNA binding dyes Hoechst 33258 or DAPI for comparison with conventional Giemsa stain. Fluorochrome-treated preparations were examined by incident ultraviolet fluorescence microscopy and the Giemsa-stained preparations by dark-ground light microscopy. Chlamydial inclusion bodies could be identified unambiguously as early as 18 hours after infection of HeLa 229 cells using either Hoechst 33258 or DAPI but not until some 48 hours in Giemsa-stained preparations. The DNA rich chlamydial elementary bodies in infected egg yolk suspension were readily detected using Hoechst 33258. The fluorescent dye technique was simpler and more rapid than Giemsa staining. Using Hoechst 33258 it is possible to speed up the identification of chlamydial isolates growing in tissue culture.