Abstract
Trypan blue is a dye that has been widely used for selective staining of dead tissues or cells. Here, we show that the pore-forming toxin HlyII of Bacillus cereus allows trypan blue staining of macrophage cells, despite the cells remaining viable and metabolically active. These findings suggest that the dye enters viable cells through the pores. To our knowledge, this is the first demonstration that trypan blue may enter viable cells. Consequently, the use of trypan blue staining as a marker of vital status should be interpreted with caution. The blue coloration does not necessarily indicate cell lysis, but may rather indicate pore formation in the cell membranes and more generally increased membrane permeability.
Highlights
Trypan blue is a diazo dye that has been widely used to color dead tissues or cells selectively
We have previously shown that HlyII induces macrophage apoptosis after 24 h incubation [18] and this seemed in apparent contradiction with a trypan blue staining as indicator of cell death after 2 h of incubation
If the trypan blue dye staining reflects cell death as usually described, the cells should be already dead after 2 h of incubation with the toxin, and be unable to undergo apoptosis subsequently
Summary
Trypan blue is a diazo dye that has been widely used to color dead tissues or cells selectively. Trypan blue dye is described as being a vital stain allowing discrimination between viable cells and cells with damaged membranes that are usually considered to be dead cells. Several bacterial pore-forming toxins can cause host cell damage by perforating the host cell membranes [1,2,3].
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