They come from soil mold - not mold in today's scientific sense of all being fungus - but mold as understood by today's laypeople and yesteryear's scientists (and maybe tomorrow's scientists too).
The soil molds that give us most of our beta lactam antibiotics are actually bacteria that so resemble the white thread-like fungus mold in appearance and habits that they seem kissing cousins.
And several hundred million years some of those kisses exchanged must have included enough initimate bodily fluids that at few fungus species picked up the DNA genes that make beta lactams.
The best known result is The Big Dog of all antibiotics : Penicillin itself.
The process is called HGT (horizontal gene transfer) - and it was Dr Martin Henry Dawson's hard slug effort in keeping this new concept before a bored and doubting scientific community that is Dawson's main claim to fame today.
No such fame for his equally hard slog to defend, before a hostile and doubting wartime scientific community, of the full worthiness of primitive penicillin made by the primitive penicillium.
His efforts, supported at crucial junctions by Dante Colitti and the Hearst media chain, by the WPB and by Pfizer, gave us all of our wartime penicillin and still provides us with almost all of our antibiotics, 75 years later.
But since Dawson's support for the overlooked, the under estimated, the unappreciated was life long affair, all of one piece, this perhaps appropriate.
In September 1940 ,Dawson's fifteen year interest in the under estimated survival abilities of avirulent microbes seemed totally unconnected to to his ten years commitment to the betterment of the unappreciated chronic ill poor in the big city holding tanks cum hospitals.
But on October 16th 1940, his 'Divided Self', to recall William James' famous phrase, finally fused.
Primitive Penicillium's 'burning and shining light'
For on that day, he injected primitive penicillin from those unappreciated microbe chemists the penicillium into humanity's lowest of the low, a black and a Jew dying from a disease judged of no military significance, the Polio of the Poor, SBE - subacute bacterial endocarditis.
And like that other diffident Henry from Nova Scotia (Henry Alline) he was now 'a man on a mission', for his few years left on Earth ....