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Several species of the genus Pleurotus have been found in this laboratory to form substances inhibitory for Staphylococcus aureus.Among these were two species, Pleurotus mutilus (Fr.)Sacc.and P. Passeckerianus Pilat, obtained from the Centraalbureau voor Schimmelcultures at Baarn.An antibacterial substance formed by these fungi was isolated in crystalline form from culture liquids; it was named pleuromutilin.P. mutilus grown on corn-steep, thiamine-peptone, or potato-dextrose agars for two days and tested by the streak-method, markedly inhibited Staphylococcus aureus, inhibited incompletely Mycobacterium smegma, and had no effect on Escherichia coli.Agar disks cut from colonies 10 days old formed inhibition zones 20 mm. in diameter with S. aureus and a small zone of incomplete inhibition with M. smegma.P. Passeckerianus produced similar zones of inhibition.Still Cultures.--P.mutilus was grown at 25C. in 2800 ml.Fernbach flasks containing beech-wood shavings and a corn-steep medium.'About four weeks after inoculation the mycelium covered the surface of the liquid and the activity against S. aureus was about 512 dilution units per ml.Reflooding the mats with fresh corn steep medium resulted in as high ac- tivity in about one week after reflooding.The reflooding was repeated at about 10-day intervals until the mat became so thick that the operation was difficult.The flasks inoculated with P. Passeckerianus reached an activity of 256 dilution units per ml. in about one month.
Kavanagh et al. (Sat,) studied this question.