1 Microbiology: Definition & History
Definition & History of Microbiology
Introduction to Microbiology
Definition: Microbiology is the scientific study of microorganisms, also known as microbes.
Scope: This field encompasses a wide range of topics, including:
Microbes in relation to humans, specifically focusing on:
Infection: How microorganisms cause disease.
Symbioses: The various beneficial or harmful interactions between microorganisms and other living macroscopic organisms.
History of Microbiology: Key Figures and Discoveries
Antoni van Leeuwenhoek (Late 1600s)
Contribution: Credited with the first visualization of microorganisms.
Method: Developed a simple microscope.
Background: A cloth merchant whose initial motivation was merely to visualize the quality of cloth, which led him to grind his own glass lenses to achieve higher magnification.
Observations: Observed what he called "animacules" (small animals) and detailed structures like fleas.
Louis Pasteur (Late 1800s)
Contribution: Revolutionized microbiology by disproving the theory of spontaneous generation.
Spontaneous Generation: This was a long-held notion that nonliving matter could spontaneously give rise to living organisms.
Swan Necked Flask Experiment (Pasteur's Experiment):
Procedure:
He boiled broth within specially designed swan-necked flasks to sterilize it by killing any existing organisms.
The bent necks of the flasks allowed for essential gas exchange (air could enter and exit) but crucially prevented the introduction of airborne dust and microbes directly into the broth.
These flasks were left open and undisturbed for months (a year and a half) under a staircase; no contamination was observed, proving the sterility of the broth.
Demonstrating Contamination: To show airborne contamination:
He broke the necks of some flasks, exposing the broth directly to the air, which quickly led to contamination.
He tilted other flasks, allowing the dust and microbes trapped in the swan neck's bend to come into contact with the broth, resulting in contamination.
Significance: This experiment definitively established that living organisms arise only from pre-existing living organisms, not spontaneously from non-living matter.
Robert Koch (Late 1800s)
Contribution: Pioneer in establishing the link between specific microbes and specific diseases, formulating the "Germ Theory of Disease."
Initial Discovery: First discovered the bacterium responsible for Anthrax.
Research Method: Studied disease in infected animals.
Observation: Noticed that every case of anthrax he studied had the same rod-shaped bacterium present in the blood samples of the diseased animals.
Germ Theory of Disease: Proposed that specific microorganisms cause specific diseases.
Koch's Postulates
Definition: A set of four criteria used to rigorously demonstrate that a particular microorganism causes a particular disease.
First Use: Initially applied and established with anthrax.
Limitations: It's important to note that these postulates do not work for every pathogen (e.g., diseases like Tuberculosis and Leprosy present challenges).
The Four Postulates:
Presence: The suspect organism must be found in every case of the disease but be absent from healthy individuals.
Isolation: The suspect organism must be isolated and grown in a pure culture (meaning grown alone, without other organisms, away from the animal's body).
Inoculation: When the pure culture is introduced into a susceptible healthy animal, it should initiate the characteristic disease symptoms.
Re-isolation: The organism must be reisolated from the experimentally infected animal, cultured in the lab, and determined to be identical to the original organism.
Problems with Koch's Postulates
Carriers: Some individuals can harbor and transmit a pathogen without displaying disease symptoms themselves (e.g., Typhoid Mary, or Staphylococcus species found in the human throat as part of normal flora).
Normal Flora/Unculturable Organisms: Some pathogenic organisms cannot be grown in pure culture outside of a host (e.g., the bacterium causing leprosy, Mycobacterium leprae, and many other symbiotic environmental bacteria).
Host Immunity: If the susceptible animal is immune to the pathogen (e.g., due to prior exposure or vaccination), the characteristic disease symptoms will not be caused even if the pathogen is introduced, violating the third postulate. Some organisms are also host-specific.
Other Significant Figures in Microbiology History
Francesco Redi (Late 1600s):
Contribution: Conducted pioneering experiments using decaying meat to challenge spontaneous generation, showing that maggots only appeared on meat exposed to flies.
Experiment: Used three flasks:
Unsealed flask: Maggots appeared.
Sealed flask: No maggots appeared.
Flask covered with gauze: Maggots appeared on the gauze, but not on the meat, demonstrating that something from the air (flies) was needed.
John Needham (1700s):
Contribution: Performed experiments similar to Pasteur's but failed to disprove spontaneous generation.
Flaw: Did not boil infusions effectively enough to kill all existing microorganisms (endospores were often overlooked).
Lazzaro Spallanzani (1700s):
Contribution: Contradicted Needham, with experiments similar to Pasteur's.
Method: Sealed flasks containing broth and boiled them, finding no contamination, further challenging spontaneous generation.
Eduard Buchner (1800s):
Contribution: Demonstrated that enzymes (cell-free extracts) could carry out fermentation, leading to the field of biochemistry.
Hans Christian Gram (1800s):
Contribution: Developed the Gram stain technique, a fundamental procedure for classifying bacteria based on their cell wall composition.
Ignaz Semmelweis (1800s):
Contribution: Advocated for handwashing in medical settings, dramatically decreasing mortality rates in labor and delivery wards by preventing the spread of puerperal fever.
Joseph Lister (1800s):
Contribution: Introduced antiseptic surgical techniques (using carbolic acid), significantly reducing post-operative infections.
Florence Nightingale (1800s):
Contribution: Pioneer of modern nursing and established stringent hygiene standards in hospitals, especially during wartime, which drastically reduced mortality from infectious diseases.
John Snow (1800s):
Contribution: Considered the father of epidemiology; he meticulously mapped cholera outbreaks in London, identifying contaminated water pumps as the source, thereby demonstrating the spread of infectious disease through environmental factors.
Edward Jenner (Late 1700s/Early 1800s):
Contribution: Developed the first successful vaccine (against smallpox) using cowpox, laying the groundwork for immunology.
Paul Ehrlich (1800s):
Contribution: Coined the term "magic bullets" for chemicals that selectively target and destroy pathogens without harming the host, pioneering the field of chemotherapy.
The Golden Age of Microbiology (1857-1907) and Modern Disciplines
This period saw rapid advancements and the establishment of many modern microbiological disciplines:
Early Biologists (Pre-1857):
Leeuwenhoek: Taxonomy (early classification of microbes).
Linnaeus: Taxonomy.
Semmelweis: Infection control.
Snow: Epidemiology.
Pasteur (Golden Age):
Industrial microbiology
Pasteurization
Food and beverage technology
Microbial metabolism
Genetics
Genetic engineering
Koch (Golden Age):
Koch's postulates
Etiology (study of disease causation)
Ivanovsky (Golden Age):
Virology (began the study of viruses)
Beijerinck & Winogradsky (Golden Age):
Environmental microbiology
Ecological microbiology
Gram (Golden Age):
Microbial morphology (specifically related to staining for identification)
Lister (Golden Age):
Antiseptic medical techniques
Nightingale (Golden Age):
Hospital microbiology (hygiene and infection control)
Jenner (Golden Age era, overlapping):
Serology
Immunology
von Behring & Kitasato (Golden Age):
Immunology (e.g., antitoxins)
Ehrlich (Golden Age):
Chemotherapy
Fleming (Later Discovery, Pharmaceutical Microbiology):
Pharmaceutical microbiology (discovery of penicillin, though slightly after the official