Medical Microbiology

Deals with prevention, diagnosis and treatment of infectious diseases caused by infectious agents like bacteria, fungi, parasites and viruses. This field is also known as Clinical microbiology. Understanding of various infectious agents and how this agents causes the disease, development and pathogenesis of the disease are being studied under medical microbiology.

History of medical microbiology:

  • Infectious diseases caused by transfer of seed like entities was first given in the year, 1546 by Girolamo  Fracastoro. He said that the disease can be caused by direct contact or by indirect contact with the infectious agent.
  • Advancements in the field of medical microbiology actually started in the year 1888, when Pasteur institute was established in Paris. Louis Pasteur and Robert Koch are considered as father of medical microbiology due to their contributions in the field.
  • Disapproval of the spontaneous generation theory(theory which claimed that non living matter is involved in giving life to living things), Pasteurization(heating at lower temperatures- less than 100 degree Celsius)methods, vaccines for Tabbies, cholera and anthrax(caused by- Bacillus anthraces) were proposed by Louis Pasteur.
  • Specific microbes are responsible to cause a particular disease. The concept of Germ theory of Disease, was given by Robert Koch. Koch cultured various Micro-organisms in the lab that caused the disease, including bacteria, mycobacterium tuberculosis, which is known to cause Tuberculosis. He used to grow Micro-organisms on solid medium like agar.
  • Koch’s postulates:
    • Organisms suffering from the disease should have the microbes that are responsible for the diseases. Microbes should not be found in healthy organisms.
    • Pure culture must be used to isolate the Micro-organisms from the diseased organism.
    • When the Micro-organism is Administered into a healthy organism, it should confer the disease.

From the same inoculated diseased experimental host, the same Micro-organism must be isolated and it has to be identical to the original agent that was responsible for the disease.

  • Concept of anti-sepsis was given by Joseph Lister. He showed that carbolic compounds, now it’s known as phenol, can be used for wound sepsis and cleaning.
  • Extensive work on TMV(Tobacco mosaic virus) was carried by Dmitri Ivanovsky. He studied TMV and differentiated it with bacteria by preforming a simple experiment in the year 1892, where he showed that when passed through filters, larger bacteria will be retained .
  • Propagation of  polio virus in monkey kidney cell cultures was given by John Enders, Thomas Weller and Frederick Robbins.

Fields in Medical microbiology:

  1. Microbial Physiology: It deals with the studies of growth of Micro-organisms, metabolism of micro-organisms and microbial cell culture. It also deals with pathophysiology of micro-organisms and role of Micro-organisms in diseases.
  2. Microbial Genetics: It involves studying how microbial genes function. Organisation of microbial genome, it’s genomic characteristics are being studied in this field.
  3. Parasitology: involves in depth studies of parasites. Sample studies can be done using feces, blood, urine and sputum samples.
  4. Virology: It deals with detail studies of various types of viruses. Host-viral mechanisms, viruses mode of action in host, diseases caused by viruses are some aspects involved with virology.
  5. Immunology: Immune system studies, which involves studying hosts immune system and it’s role in combating pathogens and foreign substances. Antigen-antibody interactions are primarily used as diagnostic tools in diseases.

Role of Medical microbiology:

  • When a Patient experiences any signs of infections, physicians recommends medical and diagnostic laboratory procedures.
  • Antibiotic sensitivity test, direct stain or culture are the type of tests performed.
  • Different types of testing’s are performed like collection of appropriate specimen and than plating the specimen on appropriate culture medium, inoculating and sub culturing it and than performing different tests to confirm the type of disease. For example- Mantoux test is used for tuberculosis.
  • Serological, biochemical, molecular tests are performed and the types of micro-organisms associated with the disease are identified.
  • Basically it involves testing samples for the presence of infectious agents, and than performing diagnostic procedures.
  • Various subfields have different procedures, like for example- immunology procedures involves performing ELISA to detect antibodies in blood.

Types of Infectious agents:


There are certain bacteria which are essential for the human body and it’s functions. These are termed as normal flora. For example- gut microbes are involved in synthesis of vitamin k and vitamin B12. During immunocompromised conditions, this microflora can lead to infections.

Invasiveness: can spread within the host body. Structures like capsules helps them to skip phagocytosis. Toxins also help them to defend host machineries.

Immunopathology: host immune response is responsible for pathogenesis in most of the Infections.


They are obligate parasites( they require host system to grow and develop as they cannot synthesise proteins and utilize it’s own energy). Viral diseases are more common in humans, particularly in children.

Invasiveness: They require host machineries to multiply and divide. They make the host system to synthesise viral components and as a result, host machineries are destroyed by viral components leading to viral diseases.

Immunopathology: host immune response is responsible for pathogenesis in most of the Infections.


Invasiveness: mucosal tissues or keratin are the places commonly where fungi can multiply and cause the Infection.

Toxin Production: food contaminated with fungi can cause serious food poisoning.

Immunopathology: When fungal spore or hyphae are inhaled, can cause hypersensitivity.(allergy).


Much more complex than viruses and bacteria. They can cause disease via multiple routes. Example- Giardiasis- Intestinal infection- by giardia, mainly through contaminated food and water.

Applications of Medical microbiology:

  • Vaccine development: understanding pathophysiology of the disease and than preparing a vaccine against it. Basically vaccine generates a immune response which will be lacking when the body is compromised during a disease. Rubella and measles are the two common examples of diseases which have been eradicated by vaccination.
  • Diagnostic tests: cultural tests, serological tests, microscopy, PCR all this diagnosis testing helps to identify infectious agents.


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