Penicillin advertisement from World War II made an extravagant claim -- but a largely true one.
Courtesy Jo Handelsman

The three-way streak method isolates single, pure colonies of bacteria. When bacteria are diluted enough, the streaks deposit individual cells on the growing medium. The single cells then divide into visible colonies, each containing a pure culture because it derived from one cell.
Courtesy Jo Handelsman

The action of penicillin. A central colony of the fungus Penicillium notatum grew on agar for five to six days, then the plate was overlaid with a thin film of molten agar containing cells of the yellow bacterium, Micrococcus luteus. The fungus produced penicillin, creating the central zone, where the bacterium's growth was inhibited. This demonstration parallels Alexander Fleming's original observation (he saw inhibition and cellular lysis of the bacterium Staphylococcus aureus )

Courtesy Jim Deacon, Director, Biology Teaching Organisation

The helpful mold
Koch is considered the founding giant of microbiology, and for good reason. His systematic emphasis on pure culture -- of growing identical microbes and discovering their properties -- is what proved so critical to the founding of microbiology.

With the foundations laid by de Bary, Pasteur and Koch, microbiology and the sub-discipline of bacteriology flourished. Increasing knowledge of bacteria reinforced the move toward aseptic surgery and lead to the lifesaving antibiotics. In 1928, Scottish bacteriologist Alexander Fleming was growing Staphylococcus cultures in dishes while searching for an antibiotic that did not harm the patient (chemicals like iodine and chlorine were deadly to microbes -- and sometimes to patients). After he accidentally left some culture dishes uncovered, Fleming returned the next day and saw a mold that apparently had reached the dish (as Pasteur had proved) through the air.

Instead of trashing the culture as "contaminated," Fleming looked closely and saw a ring of Staph bacteria dying around the mold. He figured the mold was producing something that killed the bacteria, so he isolated the mold, named it Penicillium notatum, and tried to isolate "penicillin," as he called the bactericide, but he ran out of money and failed in that quest.

For many years the discovery remained just interesting science -- researchers could not find strains of the fungus that produced enough penicillin to make its production economically viable. A search for such strains continued into World War II, when the need for antibiotics was intense because soldiers were dying of wound infections.

Supermarket science
During the early 1940s a research group led by Kenneth Raper in Peoria, Ill., asked the local community to collect new strains of Penicillium mold.

All hail melons! Moldy Mary found penicillin in a supermarket.
Courtesy of Kenneth B. Raper and the University of Wisconsin - Madison Bacteriology Department.

A woman shopping in a market noticed a melon with a fuzzy growth of Penicillium mold and brought the sample to Raper. That strain turned out to produce unprecedented quantities of penicillin and was used in commercial production. The lives of many soldiers were saved by the penicillin that was shipped to battlefronts in Europe toward the end of World War II, and microbiologists fondly remember the strain's discoverer as "Moldy Mary" -- a beneficient counterpart to "Typhoid Mary," who unwittingly spread typhoid fever to 22 New Yorkers in the early 1900's.

Penicillin was soon dubbed a "wonder drug" because it reversed infections that would have been fatal. Other antibiotics were derived from fungi, and in 1950, the isolation of tetracycline from bacteria demonstrated that both bacteria and fungi produce chemicals to fend off competing microbes. Many other antibiotics have been developed from soil microbes, but as we'll see shortly, the use of antibiotics creates "selection pressure" on microbes, promoting the evolution of drug-resistant varieties, especially when antibiotics are misused.

Is there some pattern to the cellular structure of microbes?