I-1 Introduction to medical microbiology

What is medical microbiology?

Microbiology is defined as the “study of microorganisms”. Microorganisms refer to those organisms that are too small to be seen by the unaided eye. When we are talking about “medical” microbiology, the term refers to “a subfield of microbiology which investigates microbes and other agents that are causing infections in humans and/or being present in the human body as part of the normal microbiota.

Significance of medical microbiology

The significance of medical microbiology is huge. As a benefit of this study, we have elucidated, prevented, and treated infection by microorganisms, which are frequent and often severe causes of morbidity and mortality. Especially nowadays, we can feel the significance of this subject during a pandemic. Aside from them, we have received benefits from this subject, for example, in the production of foods and fuels, or the drug industry.

Subfields of microbiology

Microbiology is subdivided into some subfields depending on the target of the investigation. Bacteriology is one of the subfields, which investigate prokaryotic unicellular microbes. Like this, other subfields are defined as below.

• Bacteriology: bacteria - unicellular microorganisms that are grouped as prokaryotes
• Virology: virus - subcellular infectious agents that can only replicate inside the cells of living organisms
• Mycology: funghi - eukaryotic unicellular microbes - yeast, molds, and mushrooms
• Parasitology: parasite - an organism that lives on or inside another organism and derives nutrients at the host’s expense.
• Protozoa: eukaryotic unicellular microbes - classified in the protozoa kingdom
• Helminth: eukaryotic multicellular organisms - classified in the animal kingdom
• Prion: subcellular infectious proteins. Unlike others, they do not contain genetic material. Instead, they induce abnormal folding of normal cellular proteins, accumulating protein aggregates in the brain, and neurological dysfunction.

A brief history of microbiology

Anton van Leeuwenhoek

He was a Dutch scientist who is widely regarded as the “father of microbiology”. He made significant contributions to the field of microscopy and is best known for his pioneering work in observing and describing microorganisms. He also described blood cells in human blood and spermatozoa in semen.

Edward Jenner

He was an English physician and scientist who is best known for developing the smallpox vaccine. He noticed that milkmaids who had been infected with cowpox, a disease similar to smallpox but much milder, appeared to be immune to smallpox. He hypothesized that exposure to cowpox protected against smallpox.

Ignaz Semmelweis

Ignaz Semmelweis was a Hungarian physician known for his pioneering work in the field of antiseptic practices and hand hygiene in medical settings. His contributions significantly reduced the incidence of puerperal fever, also known as childbed fever, and laid the foundation for modern infection control.

Joseph Lister

He was a British surgeon and scientist and is best known for pioneering antiseptic surgery in the 19th century. Lister's work significantly reduced the occurrence of infections and revolutionized medical practices. He introduced carbolic acid (phenol) as an antiseptic during surgery, advocating for its application to wounds, surgical instruments, and dressings to prevent infection.

Louis Pasteur

He was a French chemist and microbiologist, who found pasteurization, the germ theory of disease, vaccination, sterilization, fermentation, etc. Pasteurization is the process that involves heating liquids such as milk and wine to kill bacteria and other pathogens, thereby preventing spoilage and disease transmission. Also, his experiments helped establish the germ theory of disease, which proposed that microorganisms are the cause of many diseases. He is credited with the development of the first vaccines for several diseases, including rabies and anthrax. He also developed techniques for sterilizing medical equipment and surgical instruments, which helped reduce the risk of infections during medical procedures. He contributed to the understanding of fermentation.

Robert Koch

Robert Koch was a German physician and microbiologist who made significant contributions to the field of microbiology and medicine. Koch’s postulates are criteria used to establish the causative relationship between a microorganism and a disease. He researched and discovered the causative agents of anthrax, tuberculosis, cholera, malaria, and sleeping diseases. 

Koch’s postulate is a four criteria designed to establish a causal relationship between a microbe and a disease.

1. The microorganism must be found in abundance in all organisms suffering from the disease but should not be found in healthy organisms.
2. The microorganism must be isolated from a diseased organism and grown in pure culture.
3. The cultured microorganism should cause disease when introduced into a healthy organism.
4. The microorganism must be re-isolated from the inoculated, diseased experimental host and identified as being identical to the original specific causative agent.

However, it is important to note that Koch’s postulates have limitations.

• They do not apply to viruses (which are obligate intracellular parasites) or asymptomatic carriers.
• Some individuals may avoid infection due to immunity or genetic factors.
• Exceptions exist, such as pathogens causing multiple diseases.

Alexander Fleming

Fleming was a Scottish bacteriologist. He is famous for discovering penicillin, the world’s first broadly effective antibiotic substance. In 1928, he observed that a bacteria-destroying mold (penicillin) inhibited bacterial growth.