Every year on September 17th, microbiologists and science enthusiasts worldwide celebrate International Microorganism Day (IMD). This day was established by the Portuguese Society for Microbiology in 2017 and reminds us of the importance of microbes in our world.

The Legacy of Antonie van Leeuwenhoek

The story begins with Antonie van Leeuwenhoek, a Dutch scientist whose dedication and ingenuity led to ground breaking discoveries. Despite lacking a formal university education and resources, Leeuwenhoek designed and perfected hundreds of his own microscopes. He achieved unprecedented magnification levels far beyond what was possible at the time through meticulous refinement of the lenses in his optical system.

As a result, he made ground breaking discoveries, becoming the first to observe and document the existence of microorganisms. On September 17th, 1683, Leeuwenhoek sent a letter to the Royal Society of London describing his detailed observation of the first single-cell organism. He named these organisms “animalcules” or “little animals,” now known as protozoa. His discovery marked the beginning of microbiology laying a strong foundation for the study of microbiology, and he is widely regarded as the father of this field.

Leeuwenhoek’s discoveries have transcended time and continue to inspire biologists today. Despite ongoing debates among microbiologists and phylogeneticists, we are finally beginning to unlock the answers to the questions that Leeuwenhoek pondered: “Where did this multitude of tiny ‘animals’ come from, why such variety in size and behaviour; how to distinguish and classify them?”.

International Microorganism Day Mascots
The IMD Mascots (left to right: Bak, Saca, Gillus and Rizzo).

Meet the Interntional Microorganism Day Mascots

To represent the roles of microbes, IMD has four mascots – Bak, Saca, Gillus, and Rizzo. These characters symbolise the positive impact of microbes on our everyday existence.

Bak: Inspired by the Bacillus genus, which usually has a rod-like shape. While it’s true that some bacteria from this genus might give us food poisoning, such as Bacillus cereus, many others are incredibly important for our well-being, helping us maintain healthy skin, digestive tract, and airways.

Saca: This mascot takes inspiration from a type of fungi called Saccharomyces yeasts, known for their role in making bread, beer, and wine. It’s essential to remember that not all yeasts are friendly, as some can cause infections, such as candidiasis caused by Candida albicans.

Gillus: Introduced in the 2020 edition of IMD, Gillus represents the Aspergillus genus of moulds commonly found in decaying vegetation. Unfortunately, it can cause aspergillosis in individuals with weakened immune systems.

Rizzo: The latest addition to the IMD mascot family, takes inspiration from Rhizobia, a group of bacteria that establishes a mutually beneficial relationship with legume plants. This relationship involves the legumes providing nutrients to the rhizobia and in turn, the bacteria fixes nitrogen gas from the atmosphere and supplying it to the legumes in a form that is easily usable – benefiting both the bacteria and the plants.

Celebrating International Microorgansim Day

Since 2018, IMD has been organising physical and online events for people of all ages to celebrate the wonders of the microscopic world. There are various activities available to explore and appreciate the fascinating world of microorganisms, including outdoor fairs, art competitions, and hands-on experiences.


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