10 Forgotten Discoveries by Alexander Fleming That Have Nothing to Do With Penicillin

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By Trista - November 13, 2025

Before his groundbreaking discovery of penicillin, Alexander Fleming made significant contributions to understanding the body’s innate defense mechanisms against bacterial infections. In 1921, while suffering from a cold, Fleming observed that a drop of his nasal mucus, when introduced to a bacterial culture, inhibited bacterial growth. This led to the identification of lysozyme, an enzyme present in human tissues and secretions such as saliva, tears, and mucus, capable of breaking down bacterial cell walls. Fleming’s research demonstrated that lysozyme’s antibacterial properties were more effective against certain non-pathogenic bacteria, highlighting the body’s natural ability to combat infections. (britannica.com)

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Lysozyme: The Enzyme Hidden in Tears

10 Forgotten Discoveries by Alexander Fleming That Have Nothing to Do With Penicillin — Lysozyme crystals stained with methylene blue. Source: Wikipedia

In 1922, Alexander Fleming discovered lysozyme, an enzyme with antibacterial properties, in human bodily fluids such as tears and saliva. He observed that a drop of his nasal mucus, when introduced to a bacterial culture, inhibited bacterial growth. Fleming named this substance “lysozyme” due to its ability to lyse (break down) bacteria. He also found lysozyme in other human secretions, including saliva and mucus, highlighting its role in the body’s natural defense mechanisms. (aai.org)

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Unmasking the Limits of Antiseptics in WWI

During World War I, Alexander Fleming observed that commonly used antiseptics, such as carbolic acid, were ineffective in sterilizing deep, jagged wounds. He demonstrated that these antiseptics often failed to eliminate bacteria in such wounds and, more critically, destroyed the body’s white blood cells, which are essential for fighting infection. This led to increased mortality rates among soldiers. Fleming advocated for cleaning wounds with mild saline solutions to preserve the body’s natural defenses. (sciencehistory.org)

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Inventing Sensitive Bacterial Culture Plates

Alexander Fleming enhanced the design of blood agar plates, improving the cultivation of bacteria for microbiological research. By adjusting the concentration of agar and modifying sterilization methods, he created more reliable culture media. These innovations facilitated the growth and study of various bacterial species, advancing the field of microbiology. (pubmed.ncbi.nlm.nih.gov)

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Clarifying the Role of Staphylococcus

During World War I, Alexander Fleming observed that Staphylococcus bacteria were prevalent in infected wounds, often leading to severe complications. He noted that these bacteria could be present in the blood of about a quarter of the more severe cases. (history.rcp.ac.uk) Fleming’s research highlighted the dangers of Staphylococcus infections, emphasizing the need for effective treatments. His work laid the foundation for future developments in combating bacterial infections.

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Revealing the Double-Edged Sword of Hydrogen Peroxide

During World War I, Alexander Fleming cautioned against the improper use of hydrogen peroxide for wound care. He observed that, while hydrogen peroxide effectively cleansed wounds by removing debris, it also damaged healthy tissue, hindering the natural healing process. Fleming’s insights highlighted the need for more effective and tissue-friendly antiseptic methods. (enviroliteracy.org)

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Pioneering the Use of Bacteriophage Therapy

In the early 20th century, Alexander Fleming investigated bacteriophages—viruses that infect and destroy bacteria—as potential therapeutic agents. He observed that these viruses could effectively target specific bacterial strains, offering a promising alternative to antibiotics. Fleming’s research laid the groundwork for phage therapy, which has seen a resurgence in recent years due to increasing antibiotic resistance. His pioneering work continues to influence the development of targeted treatments for bacterial infections. (en.wikipedia.org)

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Insight into Nasal Infections and Mucous Defenses

In 1921, Alexander Fleming discovered that nasal mucus contains lysozyme, an enzyme capable of breaking down bacterial cell walls. He observed that when he added a sample of his own nasal mucus to a bacterial culture, the bacteria surrounding the mucus were destroyed, creating a clear zone. This finding highlighted the body’s natural defense mechanisms against infections. (sciencehistory.org)

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Exploring Non-Specific Immunity

In 1921, Alexander Fleming discovered lysozyme, an enzyme present in human tissues and secretions such as saliva, tears, and mucus, capable of breaking down bacterial cell walls. He observed that a drop of his nasal mucus, when introduced to a bacterial culture, inhibited bacterial growth. This finding highlighted the body’s natural defense mechanisms against infections, laying the groundwork for the concept of innate immunity. (britannica.com)

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Identifying Natural Growth Inhibitors for Bacteria

In his research, Alexander Fleming identified lysozyme, an enzyme with antibacterial properties, in various bodily fluids, including nasal mucus, tears, saliva, and milk. He also found lysozyme in egg whites, noting its presence in other substances like turnip juice. Fleming demonstrated that lysozyme could inhibit bacterial growth, contributing to early food safety science by highlighting natural antibacterial agents in everyday foods. (aai.org)

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Conclusion

Alexander Fleming’s scientific legacy extends far beyond his discovery of penicillin. His work on lysozyme, an antibacterial enzyme found in human tissues, and his critical analysis of antiseptics during World War I, underscore his profound impact on microbiology and medicine. Fleming’s unwavering curiosity and dedication to understanding the body’s natural defenses have paved the way for numerous advancements in infectious disease treatment. His contributions continue to inspire and inform medical research today. (britannica.com)

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