Antimicrobial activities of indole.

OIMOMI found that Escherichia coli 443, E. coli 5 and Enterococcus 1294 produced an ether-extractable compound active against Candida1), and applied this ether extract locally for treatment of nasal complications of the common cold and trychophytiasis of the feet.2,3) The results suggested some effect of this crude extract, which was found also to inhibit growth of staphylococci and streptococci.2,3) The purification of the active agent was attempted, and as described in this paper the main antimicrobial agent in the extract was found to be indole. E. coli 5 was grown in stationary culture in ether-washed 2.0 % peptone water (20 g of peptone was washed with 1.0 liter ether and used for preparation of the medium) for 5 days at 37°C. The cultured broth was centrifuged at 10,000 rpm for 30 minutes, and the clear supernatant (pH 8.0, 5 liters) was extracted with the same volume of ether. The ether extract was chilled to -30°C and filtered. The filtered ether solution was concentrated under reduced pressure, 10 mm Hg, and dried in a dessicator over P2O5,. The faintly yellowish-colored solid (578 mg) thus obtained was subjected to sublimation at 55°C under reduced pressure at 0.15 mm Hg for 30 minutes, yielding colorless crystals (184 mg) which were trapped in a tube in dry ice. Further sublimation of the extract gave similar crystals (362 mg), mp 53°C, m/e 117 (M+). Thus, more than 93% of the solid in the extract was obtained as crystals. The crystals had an indole-like odor and identity with indole was confirmed by comparison of the infrared spectrum, the ultraviolet spectrum and the melting point with those of an authentic sample. ZSOLNAI4) and KolvISTOINEN5) have described Table 1. Antibacterial spectrum of indole. The figures mean the minimal concentrations (r'g/ml) in inhibiting the growth completely. Microorganism 1 Staphylococcus aureus 2 Staphylococcus aureus FDA 209P 3 Microccus flavus FDA 16 4 Sarcina lutea PCI 1001 5 Corynebacterium bovis 1810 6 Bacillus subtilis NRRL B-558 7 Bacillus subtilis PCI 219 8 Bacillus anthracis 9 Bacillus cereus ATCC 10702 10 Escherichia coli NIHJ 11 Escherichia coli K-12 12 Escherichia coli K-12 ML 1629 13 Escherichia coli W 677 14 Escherichia coli JR 66/W 677 15 Escherichia freundii GN 346 16 Klebsiella pneumoniae 17 Shigella flexneri 4b JS 11811 18 Salmonella ryphi T-63