Virus, Germ, or Bacteria?

What’s the difference between a germ, a virus, and bacteria? Everyday Einstein focuses his microscope to find out.

Lee Falin, PhD
4-minute read
Episode #90


A stroll down the supermarket aisle will show you all kinds of products that promise to kill germs, others that are antibacterial, and still others that kill viruses. But which is better? What’s the difference between germs, viruses, and bacteria?>


The word “germ” is a catch-all phrase that can mean any microscopic particle that can cause illness in humans. The word germ comes from germen which means seed or sprout. That’s because early scientists studying germs thought about them as little seeds that spread between organisms. 

Not all scientists believed in this idea of germs however, which is understandable as to a 16th century scientist it might sound a little far-fetched. “Yeah, man there are like these invisible thingees that float through the air, and if they touch you, you like totally get sick dude...”

Of course the alternative theories weren’t much better. The prevailing idea at the time of germ theory was miasma theory, which held that noxious fumes from rotting matter caused disease. 

While wrong in essentials, this idea did lead to a number of reforms in sanitation in cities which slowed the spread of disease. Florence Nightingale was also a proponent of miasma theory, which helped drive many sanitary reforms in hospital wards.

While germ theory had been proposed much earlier, it wasn’t widely accepted until the late 1800s. This was thanks mainly to the experiments of Louis Pasteur and Robert Koch.

In modern times, the term “germ” isn’t widely used in formal science. Instead, disease-causing objects are referred to by what type they are. Viruses and bacteria are types of germs, as are certain types of fungi, protists, and prions.


Bacteria are microscopic, single-celled organisms which live pretty much anywhere and everywhere. There are bacteria that live in water, soil, the air, clouds, your carpet, the ocean, and inside your body. Just how many types of bacteria are there? Nobody knows. In fact, even experts in microbiology vary widely in their estimates, ranging from tens of thousands to hundreds of millions of different species. 

Fortunately, most bacteria are harmless. In fact, many bacteria are beneficial and help with metabolism and other aspects of human health. Your body actually has 10 times as many bacterial cells in it than it does human cells. 

See also: A World Tour of Lactobacillus Bacteria


About the Author

Lee Falin, PhD

Dr. Lee Falin earned a B.S. in Computer Science from the University of Illinois, then went on to obtain a Ph.D. in Genetics, Bioinformatics, and Computational Biology from Virginia Tech. 

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