Dr. Fleming, Penicillin and the Penicillium Mold

Penicillin Discovery and Killing of Gram Positive Cocci, Gonococci

Mar 28, 2009

Fleming served during WW I, as had Ehrlich and Domagk. He saw infectious disease deaths. Years later he sought remedies to these diseases. One day, a way opened to this.

It seemed like another routine day in September at St. Mary's Hospital in England. Dr. Alexander Fleming was back from vacation in Scotland. He retrieved, from discard storage, a few Petri plates and checked, for one last look, some colonies of Staphylococcus aureus bacteria, his current research interest.

What's this, he thought? A mold, yes, but this whole clear area with no Staphylococcus cells or colonies- what's happening here?

Fleming noted the large mold colony, and the clearing that radiated outward from the colony. It looked like some vapor or fluid was inhibiting or killing S. aureus. He remembered how nose drippings had lysed bacteria on an agar surface. Perhaps, this fungus made something new.

Fleming had been injecting Ehrlich's Salvarsan into syphilitic patients, it worked quite well. His thoughts probably raced at the possibility that something important was here – perhaps a new antibiotic. The mold was identified as Penicillium. The antibiotic to be named was penicillin.

Lysozyme – Fleming's First Important Research

Dr. Fleming was known first for his discovery of lysozyme, a natural compound in tears, white blood cells, tissues, and egg white to name a few. His characterization, testing and publications of lysozyme prepared Fleming for his study of bacterial inhibition by Penicillium mold .

Fleming's Research with Penicillium and Penicillin

Originally, a single spore in the lab landed on a Petri plate containing agar and nutrients. Spores germinate, grow threads called hyphae, and form a large, spreading mold colony.The mold produces more spores and becomes powdery on its surface with longs rows of spores extending outward from finger-like phialides. The overall look is of a simple paintbrush, or a hand with fingers. Click on the photos below to enlarge and see these details.

Fleming took portions of this Penicillium and scraped the surface to capture spores. Each spore can form one colony of mold. The transferred spores produced many new colonies of mold. The mold was in pure culture.

After Fleming streaked the mold across the middle of a Petri plate, he inoculated later, by wire needle, different bacteria perpendicular to the mold which had started to grow. What he saw next was fascinating. After a few more days of incubation, the different isolates of staphylococcus, streptococcus, micrococcus could not grow near, or even many millimeters from, the mold streak. The bacteria were killed. The killing zone was wide. This was great!

Growth of the mold in liquid cultures in flasks was a natural, next step. Fleming hoped the mold would release penicillin into the fluid where he could filter off the mold and retrieve clear fluid. That happened! Fluid filtrates killed bacteria on Petri plates. Later, when penicillin filtrates were dropped on infected human skin the bacteria were killed. Strangely, Fleming did not expand his research after his publication of these findings in 1929.

Summary Ideas on Penicillin

It took teams of people and great industry to mass produce penicillin. Even today, penicillin and derivatives serve to protect and defend in the face of mounting bacterial resistance to virtually all antibiotics world-wide.

Sources

NOVA Video.1986. Rise of a Wonder Drug: The development of penicillin. Public Broadcasting System

The copyright of the article Dr. Fleming, Penicillin and the Penicillium Mold in Human Infections is owned by Donald Reinhardt. Permission to republish Dr. Fleming, Penicillin and the Penicillium Mold in print or online must be granted by the author in writing.