Introduction and History of Microbiology

What is Microbiology?

Microbiology studies living organisms that are invisible to the naked eye, including bacteria, viruses, fungi, and parasites. It explores:

• Reproduction of microorganisms
• Pathogenicity (disease-causing ability)
• Physiology and chemical function
• Helpful and harmful relations with animals and the environment
• Industrial and scientific implication

Subdivisions of Microbiology

1. Bacteriology – study of bacteria
2. Mycology – study of fungi
3. Virology  – study of viruses
4. Parasitology – study of parasites

Introduction to Clinical Bacteriology

Clinical bacteriology stands as a fundamental pillar of modern medicine. It bridges the gap between clinical presentation and final diagnosis for a vast selection of infectious diseases. From routine urinary tract infections (UTI) to life-threatening septicemias, the precise and quick identification of bacterial pathogens is dominant for effective treatment.

The core mission of the clinical bacteriology laboratory is to identify and characterize bacteria from the clinical samples, determine their possible pathogenicity, and assess their susceptibility to antimicrobial agents. This process directly informs therapeutic decisions, reducing the empirical use of the broad -spectrum antibiotics—a key driver in the global fight against antimicrobial resistance (AMR).

History of Microbiology

Early Theories of Disease

• Supernatural Beliefs: Diseases were once thoughts to be punishments from gods.
• Hippocrates (460–370 BC): Illness caused by changes in air, water, soil, food, and habits (Change in environment).
• Varro (117–26 BC): Suggested “invisible particles” could cause disease via airborne inhalation.
• Fracastorius (1500s): Proposed that communicable diseases were spread by “living germs” through direct contact, animals, or contaminated objects.

Discovery of Microorganisms

• Antony van Leeuwenhoek (1632–1723): Father of Microbiology used a simple single-lens microscope to observe “animalcules.” He described bacterial shapes, laying the basis for bacteriology.

Abiogenesis vs Biogenesis

Theory of Abiogenesis (Spontaneous Generation)

• Aristotle (384–322 BC): Proposed that life originated spontaneously from non-living matter, e.g., fish from dry ponds after rain.
• Francesco Redi (1626–1697): Disproved spontaneous generation by showing maggots come from fly eggs, not meat.

Theory of Biogenesis

• Louis Pasteur (1822–1895): Demonstrated that life arises from pre-existing life. Using swan-neck flasks, he presented that broth remained sterile unless uncovered to contaminated air.

Pasteur’s Contributions

1. Microbial theory of  fermentation
2. Sterilization and pasteurization principles
3. Disease  control in silkworms
4. Vaccines for anthrax and rabies
5. Discovery of streptococci

Germ Theory of Disease

Germ Theory of Disease

It is the scientific theory that states several diseases are caused by the existence and actions of specific microorganisms (pathogens) within the body.

Key Figures and Experiments

The Germ Theory was not the work of a single scientist but was established through the work of several scientists over centuries

Scientist	Contribution
Francesco Redi (1626-1697)	His work on spontaneous generation began to challenge unscientific beliefs and paved the way for controlled experiments.
Louis Pasteur (1822-1895)	Considered the father of Germ Theory. His famous swan-neck flask experiment (1861) definitively disproved spontaneous generation. He showed that sterile broth would only become contaminated if exposed to microbe -laden air. He also developed vaccines for anthrax and rabies.
Robert Koch (1843-1910)	Provided the definitive proof. He established a set of postulates (Koch’s Postulates) that must be fulfilled to show a specific microbe causes a specific disease. 1. The microbe must be found in all organisms with the disease. 2. It must be isolated and grown in pure culture. 3. The cultured microbe should cause the disease when introduced into a healthy organism. 4. The same microbe must be re-isolated from the experimentally infected host.
Joseph Lister (1827-1912)	Applied the thought to surgery. Realizing that microbes caused infection, he established the use of antiseptics (carbolic acid) to sterilize wounds and surgical instruments, drastically falling post-surgical deaths.
Ignaz Semmelweis (1818-1865)	Demonstrated that handwashing could drastically reduce the incidence of fatal childbed fever in maternity wards, through this, ideas were rejected during his lifetime.

Exceptions to Koch’s Postulates

1. Asymptomatic carriers (e.g., Typhoid Mary).
2. Some microbes cannot be cultured in vitro (e.g., Treponema pallidum).
3. Species specificity (e.g., Brucella abortus causes abortion in animals, not humans).
4. Opportunistic infections in immunocompromised hosts.