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Introduction to Microbiology

Soc Virnyl Estela | 2024-02-10 | reading time: ~6min

Introduction to Microbiology§

Microbiology is the study of the structure, lifestyle, and diversity of microorganisms. The field also focuses on how to handle microorganisms and produce microbial culture in a laboratory or controlled setting.

Microbiology is also a discipline used to understand disease dynamics in Epidemiology and also in Biodiversity.

Historical Antecedents§

The history of biology is vast that we will only need to cover a few proponents or those that are involved in the improvement and innovation of the field. Some of them discovered new drugs because of messy accidents, and others are purely to improve food security.

Robert Hooke§

Robert Hooke is well-renowned for his book "Micrographia", a collection of his explorations and illustrations of microbes and small organisms under his microscope. His discovery from his microscope forced the realization of the existence of structures that were too small to be seen by the unaided eye.

Antoni van Leeuwenhoek§

Also known as the "Father of Microbiology", Antoni van Leeuwenhoek was probably first to observe microorganisms under the microscope of which he called animalcules. He published his works to the Royal Society in London.

Louis Pasteur§

In the 1850s, Louis Pasteur is a chemist and a microbiologist known for his works and studies about fermentation. He discovered th at wine is produced through fermentation caused by yeast cells.

He also proposed that microorganisms can cause disease and later developed a method to remove microbes from food called pasteurizat ion.

Robert Koch and Julius Petri§

Because of Louis Pasteur's work, it influenced Robert Koch who studied anthrax - a disease for cattle and sheep.

He is also one of the founders of bacteriology and discovered the bacteria responsible for tuberculosis and cholera.

His assistant, Julius Petri, designed a shallow dish we know today as the Petri dish.

Koch then proposed that there are four conditions that proved a disease is caused by a suspected bacteria. These are known as Koch's postulates.

Koch's Postulates

  1. the organism was present in every case of the disease
  2. it could be cultured outside the body
  3. inoculation of the culture caused the disease in an animal
  4. the organism could be found in that animal

Martinus Beijerinck and Dmitrii Ivanowski§

They were one of the founders of virology because of their work on tobacco mosaic viruses. They studied juices extracted from the leaves of plants infected with what is now known to be tobacco mosaic virus. They filtered the juices to remove bacteria and found that even when highly diluted, the liquid still could cause infection in plants. Ivanowski concluded that an infectious agent other than a bacterium—a filterable “virus”—led to the disease. Beijerinck called the substance “contagious living fluid.”

Wendell Stanley and Ernst Ruska§

Wendell Stanley further studied the tobacco mosaic virus and isolated the crystals of the hypothesized disease-causing agents.

Because of the invention of the transmission electron microscope by Ernst Ruska in 1933, this made it possible to observe viruses for the first time.

Ruska received the Nobel Prize in physics because of his transmission electron microcoscope.

Alexander Fleming§

The discovery of penicillin was nothing short of an accident. Alexander Fleming was busy with other things so he left his laboratory uncleaned for a few weeks.

When he returned, he noticed some of his petri dishes have fungus on them. But what interested him was there was no bacteria growing near the fungal contamination. There he identified this fungus as Penicillium rubens.

The mold or fungus produced an antibiotic substance for which he called penicillin.

Summary - Historical Antecedents§

The most crucial tool that helped progress the field of microbiology is the microscope. Without such a tool, we wouldn't have progressed our understanding of life, diseases, and influence in our lives.

Microbes are an essential part of the biosphere, each of us filled with them.

Pasteur invented the pasteurization and increased food safety and food security.

Wendell Standley discovered the crystals that caused the tobacco mosaic disease.

Ruska invented the transmission electron microscope and helped further our understanding of viruses.

Everything we know about medicine and diseases are thanks to the curiousity of those people who are always curious about the things around them.

Investigating microbial life§

Defining life§

The smallest unit of life is the cell. Life will not exist without the existence of this biological unit. But how do we define life? What are the current consensus when it comes to the field of cell biology and microbiology? The answer is still, as of today, an open question.

Currently, these are the criteria that most biologists agree to say something is "alive":

  1. Able to respond to stimuli.
  2. Able to reproduce.
  3. Maintains homeostasis.
  4. Has growth and development.
  5. Consists of cells.
  6. Has complex biochemical processes.

We will have an open discussion about these. Prepare and study and do your own research for I will ask each of you regarding the following criteria.

Cells can either be unicellular or multicellular. However, cellular complexity is best described in terms of structure rather than the number of cells.


The simplest cells are the prokaryotes. The name itself means "before the nut" as the words is a combination of two Greek words that are read as "pro" and "karyon".

These cells are simple in a sense these structures are enough for it to exist

  • plasma membrane
  • nucleoid
  • plasmid
  • cytoplasm
  • ribosomes

Additional extensions such as a "cell wall" and a flagellum may exist. Some even have hair-like extensions called as "cillia".


Eukaryotes are more complex since they have a "true nucleus" and also contain small structures called organelles of which have specific functions. A table below explains those key differences.

Key differences or similarities between a eukaryote and a prokaryote

NucleusNo nucleus
Membrane-bound organellesNo membrane-bound organelles
Unicellular & MulticellularUnicellular (also in colonies)
Circular DNALinear
Has mitochondriaNo mitochondria
Asexual and sexualAsexual

With that said, these organelles are small functional structures that help eukaryotic cells live and thrive. Functions vary from waste management to energy production.

As your task, define the function of the following membrane-bound organelles:

  • mitochondria
  • lysosome
  • vacuole
  • nucleus
  • golgi body
  • rough and smooth endoplasmic reticulum

Prepare for a quiz and an oral recitation next meeting.

Key questions§

  1. There are many membrane-bound organelles. Can you cite one example and describe its function?
  2. Do you think there are other criteria that can be added to define "life"?
  3. Research about viruses. How is it that they are not considered "alive"?
  4. We listed some notable mentions of scientists. Give another example who are also notable in this field and their contributions.
  5. What are the two modes of sexual reproduction? Define.

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