Mould broth filtrate

by jdbatson

…for convenience, and to avoid the repetition of the rather cumbersome phrase “Mould broth filtrate,” the name “penicillin” will be used.

When Alexander Fleming noticed that a colony of mold had contaminated his tray of staphylococcus bacteria, and that the bacteria near the mold had begun to die (or lyse), he did some science. He grew the mold in five kinds of sugar broth (including lactose+glucose=milk+honey), then poured a bit of each broth on a tray containing the bad -coccuses (strepto, pneumo, gono, staphylo) and watched them retreat. He tried filtering out the mold, boiling the mixture, and then diluting it 600-fold, and still it killed bacteria. Injects huge quantities of filtered moldy broth in mice and then rabbits–seems nontoxic. Upgrades to putting drops into some bold man’s eye every hour for a day–no problem. The mold-water kills bacteria and is safe for humans. Time to write the paper and tell everyone.


But what to call the elixer? As he later writes in the intro, the phrase “mould broth filtrate” is rather cumbersome, not to mention seriously gross. As drug companies know, a sexy name is key to convince people to put something in their bodies (compare “botox” to “botulinum toxin”). But “mold” is also too general, as a half-dozen other molds he tested had no anti-biotic effects (asparagus soup is good for you, aspergillus fumigatus soup, not so much). He knew the name he picked would become famous, and as any political spinster or derridaian graduate student can tell you, the choice of name matters a great deal.

There were a few ways he could have selected a name.

1. Named after a person

It would be presumptuous to call it the “Fleming solution,” so he would presumably pick someone vaguely related, perhaps a teacher or already-famous person. Consider the Poisson spot, named for its greatest skeptic, or any other instance of Stigler’s law. Some ecologist named a blind precambrian arthropod “krygmachela kierkegaardi” after her favorite philosopher.

2. Named after a function

“Bacteria-killing mold” or “staph-lysing mold” or some latin equivalent. Compare “anteater.”

3. Named after an attribute

“Yellow-sporal solution.” Compare “three-toed sloth.”

4. Named after the first place you saw it

Strange in a lab, popular with diseases and lifeforms. “West nile virus” or “brazil nut.”

5. Named with an arbitrary combination of sounds.

“Quark” or “bandersnatch” or “prozac.”

Fleming decided to go with “penicillin” for the “mold broth filtrate,” derived from the name of the mold itself. Of course the Petri surprise had given itself no name, but by growing other molds known to inhabit laboratory air and comparing their appearance and lethality to his new dish, he determined that it was at least closely related to penicillium rubrum. Where did this nice latin root come from? Penicillus means paintbrush (type 3).


A light micrograph of penicillium spores.

I think that a big merit of using latin names in science is that they become free-floating signifiers. Proper names work this way too, and are popular in math–my last paper was on Khovanov homology. If you don’t know the language/person involved, then it’s just a collection of sounds whose meaning can evolve over time as your understanding of the object changes. Such is not the case for Penicillin Binding Protein.

After Fleming discovered that this mold could kill (some) bacteria while leaving human cells unharmed, people wondered just how it worked. Lots of science and about 40 years later, it became clear that penicillin disabled a bacterial protein, which was immediately named “penicillin binding protein”. But that’s totally unfair to the protein. It did its job, which turns out to be linking chains in the cell wall, long before penicillin came around. The fact that penicillin could distract the protein, leaving weak cell walls which would break like a burst like a levee under stress, is hardly a definitive feature of the protein itself. And now when these bacteria are studied with absolutely no penicillin around, a key enzyme is named after its number one enemy.

It’s like calling Lou Gherig the “amyotrophic lateral sclerosis binding man” or your brain “stroke-bait.” Just rude.

I think that’s why acronyms are so popular in the biology literature, why all the papers talk about PBP instead of penicillin binding protein. By dropping any pretense at description, “PBP” attempts to specify without prejudice about form or function or meaning. Unfortunately, this can make reading biology (and corporate reports) a pretty surreal experience, when PBP coactivates PPARy in the ARC complex.

Objectively and ahistorically yours,