A brief history of microbiology
Where it all began
In the middle of a global pandemic caused by a novel virus, it can be hard to picture a world in which microorganisms are completely unknown. And yet, humankind lived in ignorance of our microscopic companions until 1683, when Antonie van Leeuwenhoek first spotted “animalcules” cavorting in drops of water. Using the most powerful magnifying lenses built to date, van Leeuwenhoek was able to see microorganisms, but it would be centuries before their role in human health, disease, food spoilage, and more would be understood.
Early events in the history of microbiology
Over the 200 years following van Leeuwenhoek’s discovery, incremental advances demonstrated more and more convincingly that tiny creatures that could not be seen with the naked eye did exist all around us, in every niche of the environment, and were responsible for a host of effects:
In 1765, Lazzaro Spallanzani investigated whether food spoilage occurs inherently as a property of the food itself, or rather is caused by some unknown factor present in the environment. To do this, he boiled broth and placed it in sealed or unsealed jars and found that only the broth in the unsealed jars became cloudy and spoiled, demonstrating that an environmental factor was responsible for this phenomenon.
In 1847 Ignaz Semmelweis recommended that doctors and surgeons wash their hands in dilute chlorine solutions to reduce the transmission of an as-yet-undefined harmful factor from autopsied corpses to living patients; this simple measure reduced the rate of mortality at his hospital four-fold within a year.
In 1849 John Snow single-handedly created the field of epidemiology by carefully analyzing patterns of cholera in London and concluding that, rather than arising from “miasma” (unhealthy air), this disease was in fact transmitted by an unknown factor in water, as it appeared to spread throughout the population from water-drawing sources.
In 1857, Louis Pasteur definitively debunked the theory of “spontaneous generation,” in which an airborne “life force”of some kind was thought to be responsible for contamination and spoilage, by performing an experiment similar to Spallanzani’s but with specially designed swan-neck flasks. These flasks had a long, curved neck designed to trap environmental microbes and prevent them from entering the flask, while still allowing air to enter. Broth boiled in these flasks remained clear and unspoiled unless the swan neck was snapped off, thus proving that microorganisms, and not a life force in the air, was responsible for these effects.
Pasteur’s seminal experiments indisputably demonstrated a cause-and-effect link between microorganisms and food spoilage, and this milestone can be considered the birthday of microbiology as a science.
More recent milestones in the history of microbiology
As microbiology established itself as a discipline, a series of key inventions and discoveries led to its expansion and application:
In 1882, Robert Koch defined Koch’s postulates, which are the criteria used to define a causal link between a disease and a specific microorganism.
In 1884 Christian Gram reported a staining protocol, now referred to as Gram staining in his honor, that distinguishes broad classes of bacteria with different cell membrane composition. These two classes of bacteria are referred to as “Gram-positive” and “Gram-negative,” and Gram staining is routinely used in the clinic and in research settings today to characterize bacteria.
In 1892, Dmitri Ivanowski discovered the first known virus, tobacco mosaic virus. Until that point, all known infectious microorganisms were bacteria, so the discovery of a much smaller infectious factor that turned out to be only one example of a host of infectious agents was revolutionary.
In 1928, Alexander Fleming discovered penicillin, the first antibiotic. The serendipitous discovery of this substance, which is naturally produced by some molds, would eventually lead to an explosion in the number of naturally and artificially produced antibiotics that are now available for manipulating and controlling bacterial proliferation.
The last milestone of the 20th century is the sequencing of the first complete bacterial genome. In 1995, the genome of Haemophilus influenzae, the bacterium that causes flu, was published by the Institute for Genomic Research, yielding unprecedented insight into a microbe at the molecular level.
Importantly, as the world of microbiology has continued to expand, we have learned more and more about the role of microbes beyond medical concerns; for example, the positive (fermentation) and negative (food safety) effects that microorganisms have in the food industry. These discoveries are facilitated in part by the increasing sophistication of the tools we have for identifying and describing microbes, as discussed in more detail in the following section.
The expanding taxonomy of microbes
In the early days of microbiology as a scientific discipline, different microorganisms were primarily distinguished by the physical appearance of the colonies that they formed on growth media. For example, an organism could be described by the general shape of the colony, whether round, filamentous, irregular, or rhizoid. Colonies could also be described in terms of how high they grew off the surface of the media, also known as their elevation; some common elevation patterns include raised, flat, or convex colonies. A third parameter that was often used to describe colony appearance is the shape of the colony edges, such as whether they are smooth (entire) or lobate.
The ability to observe microbe colony shape, morphology, and more was made possible by the development of pure culture techniques and the formulation of specific culture media. Later advances led to the ability to differentiate and identify microorganisms based on their metabolism, not just their appearance. The taxonomists put this new tool to work, and the number of known species grew from dozens, to thousands, to millions, and now potentially to the billions. These enhanced discovery tools led to an acceleration not only in the identification of species, but also of their consequences on human health and activities, their natural habitat, and contamination routes. As modern technologies continue to develop, they can emulate, accelerate, and democratize this expertise.
For three centuries we developed our ability to observe, characterize, and Identify microorganisms. Contemporary molecular biology and other advanced analytical techniques have continued to shed new light on these early findings and will undoubtedly continue to generate masses of new information on the identity of microorganisms and how they interact with humankind and our environment.