The antibacterial properties of hops (Humulus lupulus) have been recognized for many years in connection with their use in brewing. From a petroleum ether extract an active principle, "lupulon," is readily crystallized.1 Brewers2 report that lupulon is 29,000 times more effective than phenol in restricting acid production by Lactobacillus bulgaricus. Added to agar or to Dubos' liquid medium,3 lupulon inhibits the growth of most common fungi and many gram-positive bacteria; it also inhibits several acid-fast organisms, including the tubercle bacillus.
Chin4 and associates of the Division of Experimental Therapeutics, University of California, have tested the therapeutic effects of lupulon on experimental tuberculosis in mice. Samples of crystalline lupulon were titrated for their in vitro effects on Mycobacterium tuberculosis. Added in serial dilutions to Dubos' fluid medium, each sample inhibited the growth of the H37Rv strain of the tubercle bacillus in dilutions as high as 1: 40,000.