Left: Artificial mixture of F. tularensis subsp. tularensis (Schu S4, red circle) and F. philomiragia (ATCC 25017, green circle), phase contrast microscopy. Right: Fluorescence microscopy after hybridization with probes Bwall1448-Cy3 and Bwphi1448-6-FAM with 50% formamide. The green, pleomorphic cells of F. philomiragia can be easily distinguished from the smaller, coccoid rods of the highly virulent F. tularensis subsp. tularensis strain showing red fluorescence.