Problem: Nigrosine is a dye that is negatively charged. Staphylococcus aureus, like most bacteria, are also negatively charged. If S. aureus were stained with nigrosine, what would you expect to see under a bright-field microscope? A. clear cells with a dark nucleus B. purple Gram positive spheres. C. dark cells with a clear background D. clear cells with a dark background E. all dark purple/black: dark cells and background