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Several well-known medicines came from microbes living in ordinary soil. One of them, avermectin, came from a single sample of earth collected near a golf course in Japan. In 2024 its derivative, ivermectin, reached more than 170 million people for river blindness alone. This post covers what Satoshi Omura actually did, works through two numbers from the original paper, and ends with what you can borrow from his way of working.
Who is Satoshi Omura?
His Nobel Prize facts page says Omura was born on 12 July 1935 in Yamanashi Prefecture, Japan. He holds two doctorates, in pharmaceutical science from the University of Tokyo (1968) and in chemistry from the Tokyo University of Science (1970), and has worked mainly at Kitasato University in Tokyo.
His Nobel biography adds details worth knowing. After graduating, he taught evening classes at a Tokyo high school and was struck by students who arrived with oil-stained hands after a full day's work. That pushed him back into study. Because the only NMR machine in the country was busy by day, he was allowed to use it at night, and became skilled at working out the structures of molecules. A post in a fermentation laboratory, where yeast turned sugar into alcohol overnight, started his lifelong interest in microbes. From 1965 he worked at the Kitasato Institute.
What did Omura actually discover?
The 2015 Nobel Prize in Physiology or Medicine was split. According to the Nobel press release, one half went jointly to William C. Campbell and Omura "for their discoveries concerning a novel therapy against infections caused by roundworm parasites", and the other half to Tu Youyou for malaria. Our post on Tu Youyou and artemisinin covers that half.
The press release describes Omura's part. He focused on Streptomyces, soil bacteria already known for antibacterial compounds such as streptomycin. He developed methods to culture them at large scale, isolated new strains from soil samples, characterised many thousands of cultures and picked about 50 of the most promising for testing. Campbell, a parasite biologist in the USA, found that one culture was remarkably effective against parasites in farm and domestic animals. The active agent was purified and named avermectin, then chemically modified into ivermectin.
Where did the soil come from?
The biography says the microbe was isolated from a soil sample collected at the edge of a golf course at Kawana in Ito City, Shizuoka Prefecture. It was sent to Merck's research laboratories in the USA, where it showed strong activity against a nematode worm in a mouse model.
The partnership was itself one of Omura's ideas. After a sabbatical from 1971 at Wesleyan University in the USA, working with chemist Max Tishler, he proposed that a company fund his laboratory's search for new compounds. The company would develop them, and royalties would return to his group if a compound sold. The biography credits Tishler with helping set up that arrangement with Merck.
Worked example: two numbers from the 1979 paper
The discovery was published in 1979 by Burg and colleagues, with Omura as a co-author, in Antimicrobial Agents and Chemotherapy. Its abstract gives two figures you can work with.
Dose. The avermectin complex was fully active against a gut nematode when fed to infected mice at 0.0002% of the diet. As a fraction, 0.0002 / 100 = 2 × 10⁻⁶. In 1 kg of feed (1,000,000 mg) that is 2 × 10⁻⁶ × 1,000,000 mg = 2 mg, or 2 parts per million by mass.
Yield. Changing the growth medium and selecting better strains raised the amount in the fermentation broth from 9 to 500 micrograms per millilitre. 500 / 9 ≈ 56, so the yield rose about 56-fold.
The second number matters as much as the first, because a potent molecule is no use if the fermentor makes too little of it. The NCERT Class 12 chapter Microbes in Human Welfare describes this step: antibiotics are produced industrially by growing microbes in very large vessels called fermentors.
Common slip: to turn a percentage into ppm, multiply by 10,000 (0.0002 × 10,000 = 2 ppm). Multiplying by a million because "ppm has a million in it" gives an answer 100 times too big. Write the plain fraction first, then convert.
Why does it matter for NEET biology?
The NCERT Class 12 chapter Human Health and Disease names Ascaris, the common round worm, and Wuchereria, the filarial worm, as helminths that cause disease in humans. Wuchereria causes elephantiasis, or filariasis, one of the two diseases the Nobel press release links to ivermectin.
The scale today is large. The WHO fact sheet on onchocerciasis (river blindness) says that in 2024 at least 252.3 million people required preventive treatment, and treatment reached 171.6 million people in 26 countries. Merck donates ivermectin under the brand name Mectizan, and WHO's strategy needs at least 80% treatment coverage, kept up for 10 to 15 years, to stop transmission.
If parasite life cycles feel like a list of names, the Fermi Concept Library covers every concept in biology, so you can see how a vector, a host and a larva fit together before you memorise them.
What can a student take from Omura's way of working?
Volume with judgement. He screened thousands of cultures but sent on only about 50. Doing many practice questions works the same way only if you sort out which ones taught you something.
Fix the bottleneck. A potent compound still needed a 56-fold rise in yield to be useful. In your own preparation the weak link is often speed or accuracy, not knowledge.
Work across the boundary. Omura's microbiology became a medicine because it met Campbell's parasitology. Biology and chemistry chapters connect the same way in exam questions.
Next step: open the NCERT chapter on Human Health and Disease, find the section on helminths, and write one line on how each named worm reaches its host.
