An Overview of Microbiology

Definition, History, Classification and Fun Facts About Microbiology

Petri dish containing bacterial culture being examined with inverted light microscope in microbiology lab
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Microbiology is defined simply as the study of microorganisms, with "micro" meaning small, and "biology," referring to the study of living things. The microorganisms studied vary widely and the field of microbiology is broken down into many subfields of study.

The field of microbiology is critical to human beings, not only due to the infectious diseases caused by these microbes but because "good" microorganisms are necessary for us to live on the planet. Considering that the bacteria in and on our bodies outnumber our own cells, this field of study could be considered one of the most important areas of knowledge and study.

Types of Microorganisms - Classification

Microorganisms, or "microbes" are small living things. Most of these organisms cannot be seen by the naked eye, and until the invention of the microscope and germ theory, we had no idea how plentiful they are.

Microbes are found nearly anywhere on earth. They are found in boiling pools of water in Yellowstone and in volcanic vents at the lowest depths of the sea. They can live in salt flats and some thrive in salt water (so much for using salt as a preservative.) Some need oxygen to grow and others do not.

The world's "toughest" microorganism is a bacteria called Deinococcus radio trans, a bacteria which can withstand radiation to a phenomenal degree as its name implies, but can also survive without water, when exposed to strong acids, and even when placed in a vacuum.

Classification of Microorganisms in Microbiology

There are many different ways in which scientists have classified, and in doing so tried to make sense, of the millions of microbes in our midst.

Multicellular vs Unicellular vs Acellular 

One of the ways microbes are classified is by whether or not they have cells, and if so, how many. Microorganisms may be:

  • Multicellular - Having more than one cell.
  • Unicellular - Having a single cell.
  • Acellular - Lacking cells, such as viruses and prions. (There has been debate over whether viruses are really living things, as they cannot survive outside of a host, and prions are usually referred to as "infectious proteins" rather than microbes.)

Eukaryotes vs Prokaryotes

Another way in which microorganisms are classified has to do with the type of cell. These include eukaryotes and prokaryotes:

  • Eukaryotes are microbes with "complex cells" which have a true nucleus and membrane bound organelles. Examples of eukaryotes include helminths (worms,) protozoa, algae, fungi, and yeasts.
  • Prokaryotes are microbes with "simple cells" which do not have a true nucleus and lack membrane-bound organelles. Examples include bacteria.

The Major Classes of Microorganisms

The different types of microbes can also be broken down into:

  • Parasites: Parasites are sometimes more frightening than other microorganisms, at least when they can be viewed with the naked eye. Parasites include helminths (worms,) flukes, protozoa, and more. Examples of parasitic infections include malaria, giardia, and African sleep sickness. Ascariasis (roundworms) are those to infect one billion people worldwide.
  • Fungi (and yeasts): Fungi are microorganisms that are in some ways are similar to plants. If you have had athletes foot or a yeast infection, you are familiar with a few fungal infections. This category also includes mushrooms and molds. Like bacteria, we also have many "good fungi" that live on our bodies and do not cause disease.
  • Bacteria: We have more bacteria in and on our bodies than human cells, but the vast majority of these bacteria are "healthy bacteria." They protect us against infection from bad or pathologic bacteria and play a role in digesting our food. Examples of infections caused by bacteria include tuberculosis and Strep throat.
  • Viruses: Viruses are abundant in nature, though the ones most people are familiar with are those that cause human disease. Viruses can also infect other microorganisms such as bacteria, as well as plants. Immunizations have decreased the risk of some frightening diseases, but others, such as Ebola and the Zika virus, remind us that we haven't begun to conquer these miniature menaces.
  • Prions: Most scientists at this time do not classify prions as microorganisms, but rather as "infectious proteins." That said, they are often studied by virologists. Prions are essentially a piece of abnormally folded protein, and may not appear frightening at first. Yet prion diseases like mad cow disease are some of the most feared infectious diseases.

History of Microbiology

What we now know about microorganisms and which will be discussed further below is relatively new in history. Let's take a brief look at the history of microbiology:

First microscope/first microorganisms visualized - The first major step in microbiology came about when van Leeuwenhoek (1632-1723) created the first, single lens microscope. Through a lens which had a magnification of roughly 300X, he was able to visualize bacteria for the first time (from scrapings off his teeth.)

Development of Germ Theory - The human body was recognized as a source of infection by three scientists:

  • Dr. Oliver Wendall Holmes found that women who gave birth at home were less likely to develop infections than those who delivered in a hospital.
  • Dr. Ignaz Semmelweis linked infections with physicians who went directly from the autopsy room to the maternity ward without washing their hands.
  • Joseph Lister introduced aseptic techniques, including both hand washing and using heat for sterilization.

Germ Theory - The two people most credited with the acceptance of the germ theory were Louis Pasteur and Robert Koch:

  • Louis Pasteur (1822-1895) - Pasteur is credited with the theory of biogenesis, noting that all living things come from something rather than the prevailing view at the time of spontaneous generation. He claimed that many diseases were caused by microbes (rather than by sin, God's anger, and other potential causes.) He showed that microorganisms are responsible for fermentation and spoilage and developed the method called pasteurization still used today. He also developed rabies and anthrax vaccines.
  • Robert Koch (1843-1910) - Koch is the author of "Koch's postulates" the scientific series of steps that proved the germ theory and which has been used in scientific studies since (with some revisions.) He identified the cause of tuberculosis, anthrax, and cholera.

Since that time, a few landmarks include:

  • 1892 - Dmitri Iosifovich Ivanoski discovered the first virus.
  • 1928 - Alexander Flemming discovered penicillin.
  • 1995 - The first microbial genomic sequence was published.

Infectious Microorganisms

When we think of microorganisms, most of us think of disease, though these little "bugs" are overall more likely to help us than hurt us. (Make sure to read about "good microbes" below.)

Until less than a century ago, and currently, in many places of the world, infections with microorganisms were the leading cause of death. The life expectancy in the United States improved dramatically over the last century not only because we are living longer, but mostly because fewer children die in childhood.

In the United States, heart disease and cancer are now the first and second leading causes of death. Worldwide, however, infectious disease. According to the World Health Organization, in low economic countries worldwide, the leading cause of death is lower respiratory infections, followed by diarrheal diseases.

The advent of vaccinations and antibiotics, plus even more importantly clean water, has lowered our concern over infectious organisms, but it would be amiss to be arrogant. At the current time, we are facing not only emerging infectious diseases, but antibiotic resistance, and many experts feel we are long overdue for the next pandemic.

Microorganisms Which are Helpful to Humans - "Good Microbes"

Though we seldom talk about it, microorganisms are not only helpful but necessary in nearly every aspect of our lives. Microbes are important in:

  • Protecting our bodies against "bad" microbes.
  • Making food - From yogurt to alcoholic beverages, fermentation is a method in which the growth if microbes are used to create food. This is one example, however, microbes are the bottom of the food chain for much of life
  • Breakdown of wastes on the ground and recycling atmospheric gases above. Bacteria can even help with difficult waste such as oil spills and nuclear waste.
  • Bacteria in our bodies are responsible for producing vitamins such as vitamin K and some B vitamins. Bacteria are also extremely important in digestion.
  • The field of cryptography is even looking at ways in which bacteria can be used as a hard drive to store information.

Not only do microbes perform many functions for us—they are part of us. It's thought that the bacteria in and on our bodies outnumber our cells by a factor of 10 to 1.

You've probably heard the latest in eating healthily. In addition to eating broccoli and blueberries, we are now been told to eat fermented foods daily, or at least as often as possible. With bacteria, there would be no fermentation.

At birth, babies do not have bacteria in their bodies. They acquire their first bacteria as they pass through birth control. (The lack of picking up bacteria in the birth canal is thought by some to be the reason why obesity and allergies are more common in babies delivered by C-section.)

If you've read the news lately it's even been postulated that the bacteria in our guts are responsible for our day to day moods. learn how to have healthy gut bacteria. The study of the microbiome is now being used to explains many things, such as why antibiotics may lead to weight gain.

Fields of Microbiology

There are several different fields within the field of microbiology. An example of some of these fields broken down by type of organism includes:

  • Parasitology - The study of parasitology
  • Mycology - The study of fungi
  • Bacteriology - The study of bacteria
  • Virology - The study of viruses
  • Protozoology - The study of protozoa
  • Phycology - The study of algae
  • Immunology - The study of the immune system

Fields of microbiology can also be broken down by scope to include a wide range of topics. A few examples among many include:

  • Microbial physiology (growth, metabolism, and structure of microbes)
  • Microbial genetics
  • Microbial evolution
  • Environmental Microbiology
  • Industrial microbiology (for example, wastewater treatment)
  • Food Microbiology (fermentation)
  • Biotechnology
  • Bioremediation.

The Future of Microbiology

The field of microbiology is fascinating and there is more we don't know. What we have perhaps gained in the knowledge the most in the field is that there is so much more to learn.

Not only can microbes cause disease, but they can be used to develop drugs to fight other microbes (for example, penicillin.) Some viruses appear to cause cancer, while others are being evaluated as a way to fight cancer.

One of the most important reasons for people to learn about microbiology is to have respect for these "creatures" which far outnumber us. It's thought that antibiotic resistance is increased due to improper use not only of antibiotics but of antibacterial soaps. And that is only when looking at the microbes we currently recognize. With infectious diseases emerging, and with our ability to travel almost anywhere in the world on three flights, there is a great need for microbiologists to be educated and prepared.

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