Mechanism of chlorpromazine binding by Gram-positive and Gram-negative bacteria

Chlorpromazine forms charge-transfer complexes with xanthene dyes in bacteria. These complexes permit the differentiation of Gram-positive and Gram-negative bacteria in both light and polarization microscopy. The birefringence induced by the charge-transfer complex might explain the molecular basis of bacterial staining.The charge-transfer complexes formed between chorpromazine and xanthene dyes accumulate in the bacterial cell, mainly inside the bacterial cell wall. The complexes give the cells a color, which depends on the chemical composition of the staining structure, and in particular the polysaccharides of the cell wall in bacteria.Metachromatic granules were seen inside Gram-positive bacteria after chlorpromazine and rose bengal staining. Although the nature of these granules remains unclear, this type of binding may have a role in the inhibition of biochemical processes in the bacterial cells.