On the Inhibitory Influence of Eosin upon Sporulation

Sporulation of B. anthracis, B. subtilis, B. cereus, B. ruminatus, B. mesentericus, B. anthracoides and B. megatherium does not take place in an agar medium containing eosin "Gelb" in a concentration exceeding 0.5 per cent. In a concentration of 0.1 per cent. most of these bacteria fail to produce spores. The greatest sensitiveness is shown by B. cereus and B. mesentericus. In a bouillon medium sporulation is likewise inhibited by eosin, but after a longer time-seven weeks or more-sporulation still occurs where the concentration of the dye equals one-tenth per cent. Sporulation of B. tetani, B. anthracis symptomaticus, B. botulismus, B. oedema maligni, B. enteritidis sporogenes, and B. putrificus does not take place in a medium containing eosin "Gelb" in concentrations exceeding 0.03 per cent. With these organisms, no difference was noted in the final effect, depending on the medium employed. No permanent loss of power to produce spores ensues with the bacteria tested even after long sojourn in the eosinized media. It may be stated that on the whole the inhibitory action of eosin was more pronounced upon the anaerobic than upon the aerobic species of bacteria employed in these experiments.