Microbiology Overview

Microbiology Overview

• Microbiology is the study of microorganisms existing as single cells or clusters.
• It includes viruses, which are microscopic but acellular.
• Sub-disciplines include bacteriology, parasitology, virology, and mycology.

Microbiology Details

• More than 90% of body cells are microbes.
• About 1 kg of bacteria are present in an average human gut.
• 8% of human DNA is derived from viral genomes.
• Bacteria in oceans outnumber stars in the universe (100 million times more) by roughly 13 x 10²⁸.
• Microbes make up about 90% of the biomass of the entire biosphere.

Brief History of Microbiology

• Early Observations:
  • Robert Hooke (1665): English scientist using a compound microscope coined the term "cells," marking the beginning of cell theory. He observed cork tissue, but his microscopes lacked staining capabilities.
  • Anton van Leeuwenhoek (1632-1723): Dutch glass merchant and scientist, invented the first simple microscope, and discovered bacteria, protists, sperm cells, and blood cells ("animalcules"). He documented these observations by writing letters to the Royal Society of London.

Spontaneous Generation Theory

• Theory: Proposed by Aristotle (350 BC): Life arises from nonliving matter (e.g., aphids from dew, fleas from putrid matter, mice from dirty hay).
• Debate:
  • Francesco Redi (1626-1697): Italian physician, naturalist, and poet who challenged spontaneous generation. His experiment using jars of meat showed maggots appeared only in open jars, where flies could lay eggs.
  • John Needham (1745): English naturalist and priest, a strong proponent of spontaneous generation who challenged Redi's experiment.
  • Lazzaro Spallanzani (1765): Italian scientist who suggested that microorganisms from air likely entered Needham's solutions after boiling, a criticism of Needham's procedure.
• Theories: Needham's experiments suggested vital force needed for spontaneous generation, but Spallanzani disagreed.

Theory of Biogenesis

• Theory: Proposed by Rudolf Virchow (1858): Living cells arise only from preexisting living cells.
• Louis Pasteur (1861): Further strengthened the theory of biogenesis with experiments demonstrating microorganisms from the air can contaminate sterile solutions; but air itself doesn't create them.

The Golden Age of Microbiology

• Time Period: 1857-1914.
• Developments: This period marked the establishment of microbiology as a formal science, with the discovery of the agents of many diseases, the identification of the relationship between microorganisms and disease, the exploration of immunity's role in disease prevention, and the understanding of microbial chemical activities.
• Techniques: Improved techniques for microscopy, microbial culture, vaccine development, and surgical procedures.

Fermentation, Pasteurization, and Germ Theory of Disease

• Pasteurization: A process for preserving liquids by heating to kill harmful bacteria.
• Fermentation: The conversion of sugar to alcohol in the absence of air (yeast involved).
• Germ Theory of Disease: A fundamental understanding that specific microorganisms cause particular infectious diseases.
• Key figures:
  • Louis Pasteur and his contributions to the Germ Theory of Disease, silkworm diseases, and fermentation.
  • Agostino Bassi (1835): identified a fungal cause for another silkworm disease.
  • Joseph Lister (1860s): pioneer of antiseptic techniques.
  • Ignaz Semmelweis (1840s): father of handwashing.
  • Robert Koch (1876): German scientist; discovered that Bacillus anthracis produces spores and created techniques for fixing, staining, and photographing bacteria. He also discovered M. tuberculosis and V. cholerae.
• Koch's Postulates (1884): A set of criteria used to prove that a specific microorganism causes a particular disease. These postulates include finding the microorganism in diseased individuals but not healthy individuals, isolating and growing the microorganism, causing the same disease in a susceptible animal after inoculation of the microorganism, and recovering the same microorganism from the experimentally infected animals.

Limitations of Koch's Postulates

• Exemptions: Certain pathogens (e.g., viruses, rickettsias, chlamydias) do not grow easily on artificial media, so they are not always straightforward to diagnose. Many others are species-specific. Some pathogenic microorganisms become less pathogenic or non-pathogenic in cultures, thus making it difficult to consistently demonstrate their ability to cause disease in experimental animals.

Explore the fascinating world of microbiology, the study of microorganisms that exist as single cells or in clusters. Delve into sub-disciplines such as bacteriology, virology, and mycology while learning about the immense impact of microbes on human health and the environment.