Contamination and Discovery in Early Twentieth-Century Bacteriology?

The French Observation

In the 1890s, Ernest Duchesne, a French medical student at the Lyon Military Hospital, observed that cultures of Penicillium mold inhibited the growth of pathogenic bacteria when grown together on laboratory medium. Duchesne inoculated animals with Penicillium cultures and noted apparent improvements in bacterial infections. He wrote a medical dissertation on the subject in 1897, titled ''Sur l'antagonisme des microbes'', but the work remained embedded in obscure institutional archives and attracted no clinical attention from the broader medical community. Duchesne died in 1912, and his observations were not repeated. The Pasteur Institute did not pursue the line of inquiry, and institutional memory of the work faded.

The question of why Duchesne's findings generated no follow-up remains contested among historians. The most direct explanation is methodological: Duchesne's evidence came from animal models rather than clinical trials, making the practical application uncertain. Laboratories of the 1890s lacked standardized protocols for extracting or purifying mold products, and the mechanisms by which mold antagonized bacteria were unknown. Some scholars argue that the work seemed too preliminary to justify the practical effort of developing it into a therapy. Others suggest that the chemical and pharmaceutical industries of the period simply had no institutional interest in mold products when chemical synthesis was advancing rapidly. The absence of a second observer was decisive; single observations from deceased researchers, lacking institutional sponsorship or clear clinical pathway, were routinely set aside.

Fleming's Contamination, 1928

In 1928, Alexander Fleming, a Scottish bacteriologist working at Saint Mary's Hospital in London, was studying colonies of Staphylococcus bacteria. One of his culture plates became contaminated with mold, a routine occurrence in pre-aseptic laboratory technique. Fleming observed that the bacterial colonies near the mold growth were dissolved and cleared. He noted this observation and set the plate aside for later study. When he returned to examine it more carefully, the plate had been washed and discarded as contaminated waste by laboratory staff. The contamination was not documented in any surviving record, and the incident passed without notice or consequence at the time.

Fleming's later work established his prominence in bacteriology, but through unrelated investigations into antibacterial substances in human secretions. His 1928 contaminated plate was recovered only in retrospective accounts written decades later, when serum therapy had become established as the only viable systemic treatment for bacterial infection. Whether Fleming actually observed the phenomenon as described, and whether he understood its significance at the time, remain uncertain. The available contemporary records do not establish that he recognized the contamination as anything but a failed experiment.

Industrial and Institutional Context

Absence and Consequence

Historical Documentation