Early Microbiology: Humoral, Miasma Theories

Historical Context of Microbiology

• Microbiology emerged as a science in the mid-1800s, driven by the need to understand and cure diseases.

• Before the mid-1800s, the Humoral Theory and Miasma Theory were the main explanations for disease.

  • The Humoral Theory attributed sickness to imbalances in the four humors: black bile, yellow bile, blood, and phlegm.
  • The Miasma Theory connected disease spread to "bad air" from decaying organic matter.

Key Figures in Early Microbiology

Antonie van Leeuwenhoek (mid-1600s)

• He was the first to observe living microbes using a single-lens microscope with ~250X magnification.
• The microscope was a simple, handheld device with a candle for illumination and a small magnifying lens between brass plates.
• Leeuwenhoek ground his own lenses but left no record of the process, making replication difficult.
• He observed protozoa and large bacteria, noting microscopic life forms everywhere.

Robert Hooke (mid-1600s)

• Credited with naming "cells," after observing plant material composed of box-like compartments.
• Hooke built the first compound microscope based on a telescope design but it was inferior to Leeuwenhoek's.

Early Medical Advances (mid-1800s)

• Oliver Wendell Holmes noted that mothers who acquired puerperal fever after childbirth were often exposed to doctors or nurses who had seen patients with the disease.
• Ignaz Semmelweis demonstrated that handwashing among doctors and nurses greatly reduced puerperal fever incidence.

Louis Pasteur (mid-late 1800s)

• Showed that fermentation is a biological process, not just chemical.
• Disproved the theory of spontaneous generation using swan-necked flasks; sterile infusions remained sterile unless the flasks were tipped, allowing microbes to enter.
• Developed pasteurization for food preservation, extending the shelf life of dairy products without refrigeration.
• Understood immunology principles through chicken cholera research and developed a rabies vaccine for humans.

Robert Koch (mid-late 1800s, Germany)

• Developed a method to connect a microscopic organism to a specific disease, which is still fundamental today.
• Understood that microbes must be grown in isolation to be studied and characterized.
• Developed sterile techniques and methods to isolate and grow bacteria in pure cultures.
• Used solidified gelatin (later agar) to create a firm surface for microbe growth without melting during boiling.

Koch's Postulates

• A procedure to determine an organism as the causative agent of a disease.
• Must find the agent in every case of the disease, showing a consistent set of symptoms.
• Isolate the disease organism in a pure culture.
• Inoculation of the culture into a healthy, susceptible animal must produce the same disease symptoms.
• Reisolate the organism from the diseased animal and show it is identical to the original isolate.

A Note on Koch's Postulates with Human Diseases

• Since experimentation is not possible on humans, animal models can be used.

  • Mice are use for Streptococcus
  • Armadillos are for leprosy

• A weight-of-evidence is used if pathogens only have human hosts.

  • A candidate pathogens leads to eventual conclusion, if associated with all cases of a disease

John Snow (mid-late 1800s, England)

• Known as the father of epidemiology.
• Was a skeptic of the Miasma theory prevalent in Victorian England.
• First to examine disease incidence in a geographic context, using maps to locate disease sources.
• During the 1854 cholera outbreak in London, Snow traced the source to a contaminated water pump and ended the epidemic by closing the pump.

Taxonomy and Naming Microorganisms

• Organisms are organized, classified, and named.
• Carolus Linnaeus published Systema Naturae in the mid-1700s, forming a uniform naming system.
• Nomenclature gives organisms scientific names and classifies organisms according to criteria.
• Binomial nomenclature gives each microbe two names.
  • Genus (noun; always capitalized)
  • Species (adjective; lowercase).
• Both the Genus and Species are italicized or underlined.
  • Staphylococcus aureus or abbreviated as S. aureus
  • Bacillus subtilis (B. subtilis)
  • Escherichia coli (E. coli) or abbreviated as E. coli

Taxonomy Classification

• Taxonomy Classifications
  • Domain
  • Kingdom
  • Phylum
  • Class
  • Order
  • Family
  • Genus
  • Species

Microbiology Overview

• Microbiology is the study of microorganisms, including: bacteria, viruses, fungi, protozoa, helminths (worms), and algae.
• Focus is often on bacteria, viruses, and sometimes fungi and protozoa.

Microscopy and Cell Types

Microscopy is useful for observation of organisms in the micrometer size range.

• Prokaryotic cells include Bacteria and Archaea.
  • Cells are biochemically different, but morphologically similar.
  • Have diameters around ~1.0 µm with no nucleus or membrane-bound organelles.
  • Most cells have a cell wall on the outside of the plasma membrane. About 50% of the biomass on Earth is prokaryotic!
• Bacteria are single-celled organisms with simple shapes, lacking membrane-enclosed structures.
  • Bacteria are located everywhere life can exist.
  • Most pathogens are bacterial, and no pathogens have been found among archaea yet.
• Eukaryotic cells include animals, plants, fungi, and protists.
  • They contain a double-membrane bound nucleus with DNA, along with membrane-bound organelles with a diameter of 10–100 µm.
• Protozoa are single-celled, microscopic organisms.
  • Have at least one nucleus and many cellular structures.
  • Engulf or ingest smaller organisms for food with most able to move.
  • Important pathogens include protozoans (dysentery and malaria).
• Fungi include yeasts, molds, and mushrooms.
  • Yeasts and molds are single-celled and microscopic.
  • Mushrooms are multicellular and macroscopic.
  • Have a cell nucleus and other cellular structures. Absorb nutrients from the environment and are widely distributed in water and soil as decomposers.
  • Some are pathogens (histoplasma and tenia).

Branches of Study Within Microbiology

• Bacteriology studies microorganism physiology and disease processes.
• Immunology studies host cell types, signals, and infection responses.
• Public health microbiology & epidemiology monitors disease incidence and recommends actions to slow spread.
• Food, dairy, and environmental microbiology examines microbe roles in food, water, and sanitation.
• Biotechnology, genetic engineering & recombinant DNA technology alters organisms for useful properties or product manufacture, like pesticide-resistant crops or insulin production.

Explore the origins of microbiology, contrasting early theories like Humoral and Miasma with the emergence of microbiology in the 1800s. Learn about the contributions of Antonie van Leeuwenhoek, who first observed microbes, and Robert Hooke. Discover how their observations shaped our understanding of disease and microscopic life.