Wednesday Notes


History Of Microbiology

The science of Microbiology began with the invention of the microscope.

  • Robert Hook (1665) – Coined the term “cell”, like a prison cell when he was the first to observe cork material from plants.
  • Anton von Leeuwenhoek (1674) – First to observe living microorganisms. He termed them “animalcules.” The picture to the right is his self made microscope. He never let anyone use, and did not teach anyone how to make them. When he died it took many years to replicate it and was partly the reason for a delay in progress.

Golden Age of Microbiology

(1857-1914) Period of time when many discoveries were made about microorganisms.

The 4 Main Questions:

  1. Is spontaneous generation (nonliving things generating living things) of life possible? 
  2. What causes fermentation?
  3. What causes disease?
  4. How can disease and infection be prevented?

Spontaneous Generation vs. Biogenesis

Spontaneous Generation- Nonliving things generating living things.

  • Francisco Redi (late 1600s) – First to document a controlled experiment. The picture to the right is the experiment he conducted, and documented.  Conclusion: Rejected hypothesis of spontaneous generation.
  • John Needham (mid-1700s) – Boiled beef gravy or plant infusions by placing them in sealed flasks & dicovered the liquids became cloudy with life/microorganisms. Conclusion: Accepted hypothesis of spontaneous generation.
  • Lazzaro Spalanzi (mid/late 1700s) – Boiled infusions more than 1 hour & then put them in very well sealed flasks. His infusions did not become cloudy.  Conclusion: Rejected hypothesis of spontaneous generation.
  • Louis Pasteur (1861) – created and used swan neck flasks to allow the passing of air/oxygen into the flasks but keep particles in the air from settling into the infusions. Conclusion: Rejected Spontaneous generation and was able to put the argument to rest.

Louis Pasteur’s other accomplishments:

  • Investigated the cause of fermentation by observing (budding yeasts) microbes in wine and other fermented foods.
  • Proved some organisms do not need oxygen to stay alive & ferment foods. These organisms are facultative anaerobes.
  • Experimented adding bacteria & yeasts to unfermented foods like grapefruit juice. Discovered that the foods did become fermented.
  • Germ Theory of Disease

The Germ Theory of Disease

Microorganisms can cause infectious diseases (Pasteur, 1857)

  • Robert Koch’s work – examined blood of animals infected w/ Bacillus anthracis (Anthrax), observing bacilli-shaped microbes in the blood. One of his most important contributions to microbiology was his postulates.

Koch’s Postulates

A series of steps that must be taken to prove the cause of any infectious disease.

  1. The suspected causative agent must be found in every case of the disease and be absent from healthy hosts.
  2. The agent must be isolated and grown outside the host.
  3. When the agent is introduced to a healthy, susceptible host, the host must get the disease.
  4. The same agent must be found in the diseased experimental host.

“agent” – can refer to any fungus, protozoan, bacterium, virus or other pathogen

Who Did What?

  • Ingaz Semmelweis: Handwashing (1848)
  • Joseph Lister: Used phenol to spray on surgical wounds to reduce infections.
  • John Snow : One of the first epidemiologists. In 1854 he investigated the source of a cholera outbreak in London. Epidemiology: “…is the study of the distribution and patterns of health-events, health-characteristics and their causes or influences in well-defined populations.” – Wikipedia
  • Florence Nightengale: Nurse during Crimean war. She was a clean freak who was the first to document her cleaning regimen and promote hygienic standards in the ward such as scrubbing floors and changing soiled clothes.
  • Edward Jenner (1796) – First to perform vaccination. (comes from the word vaca – cow, from his discovery regarding cowpox & small pox)
  • Paul Ehrlich – Searched for the “Magic Bullet” – a chemical or agent that will kill a disease causing microbe w/o harming the host.

Modern Biology

  • Biochemistry/Metabolism – Chemical reactions that take place within the cells of microbes. 
  • Molecular Biology – Genetics (study of genes) & DNA technology (in vitro manipulation of DNA)
  • Defending humans against disease
  • Environmental Microbiology
  • Industrial Microbiology (Food Industry & other products)


Culture of Microorganism & Media Preparation

Culture Media – Substance that contains nutrients for supporting the growth of microbes.

Solid Media

  • Agar that is solid at room temperature 
  • Comes from red algae
  • Discovered as a good growth media by Fanny Hess (wife/partner of Walter Hess)
  • Good growth media because it remains solid up to 45°C, melts at 100°C & microbes do not digest/degrade the agar.
  • Streak plates (petri dishes) – better to see microbes & colony morphology; however they dry out quickly.
  • “Deeps” (Deep Tubes) – are not as easy to contaminate; must stab sample to bottom of tube; better for longer storage. Cant study colony morphology.
  • Slant Tubes – Not as easy to contaminate; better for longer storage; cant study colony morphology

Liquid Media

  • Liquid at room temperature
  • Made from animal infusions.
  • Liquid media in broth tubes can also be used to predict the oxygen requirements for microbes.

Broth Tubes & Flasks – Organisms maintain their shape easily; can be extracted so that cell morphology can be studied. Samples do not get contaminated as easily. Good for calculating cell concentrations.


“An anaerobic organism or anaerobe is any organism that does not require oxygen for growth. It could possibly react negatively and may even die if oxygen is present. There are three types:

  • obligate anaerobes, which cannot use oxygen for growth and are even harmed by it
  • aerotolerant organisms, which cannot use oxygen for growth, but tolerate the presence of it
  • facultative anaerobes, which can grow without oxygen but can utilize oxygen if it is present

In humans beings these organisms are usually found in gastrointestinal tract.[1] ” – Wikipedia

“Aerobic and anaerobic bacteria can be identified by growing them in liquid culture:
1: Obligate aerobic (oxygen-needing) bacteria gather at the top of the test tube in order to absorb maximal amount of oxygen.
2: Obligate anaerobic bacteria gather at the bottom to avoid oxygen.
3: Facultative bacteria gather mostly at the top, since aerobic respiration is the most beneficial one; but, as lack of oxygen does not hurt them, they can be found all along the test tube.
4: Microaerophiles gather at the upper part of the test tube but not at the top. They require oxygen but at a low concentration.
5: Aerotolerant bacteria are not affected at all by oxygen, and they are evenly spread along the test tube.” – Wikipedia

Differential Media & Selective Media (Mannitol Salt Agar)

Selective Media – Media that promotes the growth of some types of microbes while inhibiting the growth of other types of organisms.

Differential Media – Changes colors based on types of organisms due to the pH indicators within the media

Defined Media vs. Defined Media

Defined Media: Known & measured amount of nutrients

Complex Media: Crude amounts or unknown amounts of nutrients (ex. beef broth)

Aseptic – w/o contamination or w/o microbes

Ex. Disinfecting work station; sterilizing tools


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