Abstract
B. prodigiosus is known to be one of the organisms which are resistant to triphenyl methane dyes, as well as to other classes of dyes. The experiments here recorded indicate the—perhaps not generally realized—degree of this resistance.
Careful determinations showed that growth of B. prodigiosus on agar is prevented by gentian violet∗ only when the dye is used in dilutions of 1 to 900. Compare this with B. anthracis whose growth on agar is completely inhibited by dilutions of approximately 1 to 1,000,000, and whose growth in broth is inhibited even by much weaker dilutions.
This marked resistance of B. prodigiosus to the bacteriostatic effect is paralleled by its resistance to the bactericidal effect of certain triphenyl methane dyes. That the organism (at least the strains of it usually encountered) readily survives exposure to gentian violet for periods of minutes or hours (as contrasted with Staphylococcus aureus which is killed by exposures of 45 minutes in 1 to 15,000 solution) is readily shown. Transplants made from a tube containing B. prodigiosus suspended in 2% gentian violet showed vigorous growth, though the organisms had been exposed to the dye for 4 hours.
The present report deals, however, with survival of B. prodigiosus after exposure to dye for periods of months.
In a preliminary experiment, transplants on agar made from a tube containing gentian violet (1 to 15,000) and B. prodigiosus showed the organism to be still alive and vigorous at the end of 141/2 months. In another experiment transplants made at the end of 261/2 months from a similar tube showed just as vigorous growth of the organism as if no dye whatever had been present.
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