Hey, it’s Professor Dave, let’s check out some microbes.
If you’re a living, breathing human being, you’ve probably come down with a cold at
some point in your life.
Maybe you’ve suffered from food poisoning, or chickenpox, or taken antibiotics for an
infection.
But have you ever wondered what causes these diseases?
What’s going on inside the body?
It turns out that there’s an incredibly diverse world of microscopic organisms that
exist virtually everywhere you can imagine.
They’re living right on our skin, they’re lurking in deep sea hydrothermal vents, they’re
in the soil in our gardens, on doorknobs, in our mouths and stomachs, and even in the
air that surrounds us.
That may sound a little alarming, but don’t worry, most of these microscopic organisms
are quite harmless.
Many of them are even helping you survive right now, by protecting your skin, airways,
and digestive system from foreign invaders, which are known as pathogens, and these are
the little critters that will be the main focus of this series, so let’s dive right in.
Humans have been getting diseases from pathogens since there have been humans, but it wasn’t
until we developed the technology to see incredibly small objects that we began to fully understand
the world around us.
It all began with a Dutch father-son team named Hans and Zacharias Janssen, who invented
the first compound microscope in the late 16th century.
Their device, which was essentially a tube with a lens at the top and bottom, magnified
objects somewhere between three times and nine times.
The images were pretty blurry, but their invention laid down crucial groundwork for researchers
to come.
Over a hundred years later, in the late 1600s, technology advanced such that the microscope
could magnify objects up to 270 times.
Enter Anton van Leeuwenhoek in 1674, a cloth merchant-turned-biologist who worked to improve
the microscope so that he could see his wares, which was the cloth he sold, up close and
personal.
Imagine his surprise when he accidentally discovered bacteria!
As he peered through his microscope, he noticed a new world, millions of what he called “animalcules”
in a single drop of water.
Once we could see these things, scientists began to slowly examine and classify the tiny
organisms that are all around us.
Almost a hundred years after Leeuwenhoek’s discovery, Danish biologist Otto Müller developed
a system to organize bacteria into categories, which we will get to a bit later.
Nearly a hundred years after that, in 1840, German pathologist Friedrich Henle proposed
a series of criteria to prove that microorganisms cause human disease, and this was called the
“germ theory”.
Louis Pasteur and Robert Koch confirmed Henle’s theory in the 1870s and 1880s, demonstrating
with a series of involved experiments that microorganisms are responsible for causing
diseases such as cholera, the plague, tuberculosis, and rabies.
The world that Leeuwenhoek discovered was both exciting and mysterious, harboring creatures
of all shapes and sizes, of mysterious origin and unknown purpose.
And now in the 21st century, we know that there are literally thousands of types of
microorganisms living around us, on us, and in us.
To understand how microorganisms cause disease, it’s helpful to understand the similarities
and differences among them, and the categories they fall into, so we will need to understand
this before we look at individual diseases.
Microbes can be divided into four distinct groups.
Those are viruses, bacteria, fungi, and parasites.
Viruses are the smallest of these infectious agents, ranging from 18 to 300 nanometers
in diameter.
For the most part, they can’t be seen with a light microscope, which is the regular kind
most people are familiar with, which uses visible light and magnifying lenses.
More powerful microscopy techniques are required.
With these, scientists have discovered over 100 families and 2,800 species of viruses,
and that number rises every year.
Of course, not all viruses can infect humans, so we don’t need to get overly anxious.
For more information on viruses, check out this tutorial in my biology series.
This should be enough to understand what we will discuss about viruses throughout this series.
Next up is bacteria.
These are quite different from viruses, in that they are what we call prokaryotic organisms,
which means that they are unicellular in nature.
Viruses are not made of cells, and are much smaller than even a single cell, so bacteria,
even with just the one cell, are dramatically more complicated than viruses, whose status
as living organisms is actually quite ambiguous.
Bacteria can be classified based on their shape, which can be spheres, rods, or spirals.
They can be classified by their size, typically between one and twenty micrometers, which
are millionths of a meter.
And they can also be classified by the way that they’re arranged, which can be as single
isolated cells, in chains, or in clusters of cells.
To go a little deeper, bacteria can be further classified by the genes they contain, which
we call genotypic properties, as well as the observable characteristics they display, which
we call phenotypic properties.
Just as with viruses, we did cover a reasonable amount of information regarding bacteria in
the biology series, so feel free to check out this tutorial now if you’re rusty on
the prerequisites.
Next up, fungi are even more complex than bacteria.
Fungi are eukaryotic, which means the cells that comprise them contain a nucleus, endoplasmic
reticulum, Golgi bodies, and mitochondria, unlike bacteria, which do not have these organelles
and other complex features.
Fungi sometimes exist in a unicellular form called yeast, that can replicate asexually,
or in a filamentous form called mold, that can replicate sexually or asexually.
Lastly, parasites are the most complex microorganisms.
Some parasites are unicellular, while others are multicellular.
Their life cycles can vary drastically, depending on the type of relationship they form with
their host.
Parasites can range in size from a diameter of one micrometer all the way up to ten meters
in length.
So that is a brief introduction to the types of microorganisms we will be discussing throughout
this series.
We’ve learned a bit about them already in biology, but now that we have learned all
about the human body in the anatomy and physiology series, we are ready to learn about how pathogens
interact with our bodies to make us sick.
So let’s move forward and begin to do just that.