Weapon in Mass Production

As with many great scientific findings, the discovery of penicillin by Sir Alexander Fleming came about by accident. The doctor had been studying the ability of bacteria to form strains, and, before leaving on a weekend holiday, he incubated some plates and left them to grow during his absence. When he returned, one of the plates had been contaminated by mold.

The lawn of bacteria was disturbed around dots of fungal growth, while plates that were uncontaminated remained normal. Fleming noticed this abnormal growth pattern and hypothesized that the fungi possessed some bacteria-killing property. In the face of much opposition from many of the leading medical minds of the 1930s, Fleming persisted in advocating for the development of penicillin to treat bacterial infections in men.

To this day, antibiotics are tested for their efficacy in a manner similar to that of Fleming’s mold in 1928. An agar plate is inoculated with bacteria, and a disk containing the antibiotic in question is placed on one plate before incubation. After several days, the ability of the antibiotic to slow or stop bacterial growth can be assessed, in part by measuring (in millimeters) the diameter of the circle which forms round the disk, also known as the zone of inhibition.

In addition to penicillin, Sir Alexander Fleming also found another compound with antibacterial properties, again by accident. While infected with a cold, the intrepid doctor swabbed his own mucus, plated it, and forgot about for a couple weeks. When he revisited the experiment, bacterial colonies had grown on the plate except for the areas swabbed with his mucus. It turns out that mucus, along with saliva and tears, contains enzymes known as lysozymes that destroy the cell walls of several bacteria.

Catch Him If You Can

Be Careful What You Wish For