Chapter 2 - History of Microbiology Flashcards
Upon which two basic methods is microbiology founded?
- Microscopy
- Pure culture technique
Why is microscopy important to the field of microbiology?
Microbes are very small and require microscopes to be seen
Why is pure culture technique important to the field of microscopy?
Because each individual type of microbe must be separated from others in order for study
What do we mean by resolution?
The ability of a microscope to differentiate between two objects
Who discovered microbes
Leeuwenhoek
How did Leeuwenhoek discover microbes? In other words, what type of microscope did he use?
A simple microscope with a lens of unusually high quality
Why did simple microscopes offer better quality images than compound microscopes in the 18th century?
Although compound microscopes offer many advantages, they must be made of exceptionally high-quality lens because any distoritions in the first lens are magnified by the second. Simple microscopes therefore offered higher quality images because of their lesser distortion
In what century did Leeuwenhoek discover microbes?
The 16th century
What was the principal innovation that lead to the improvement of the compound microscope?
The replacement of each of the lenses in the compound microscope with a set of lenses that were designed to correct a particular type of distortion
The final step in the evolution of the compound microscope was the development of the ________________, a device that proces an even illumination of the specimen.
Condenser
Advances in ________________ during the 19th century led to improved ____________________________.
Optics
Microscopes
Advances in ___________ ____________________ in the 20th century were largely confined to improved methods of enhancing ___________________.
Light microscopy
Contrast
What approach did scientists use to enhance contrast in the 19th and early 20th century?
Staining
What was the primary disadvantage of using staining to contrast microbial specimens?
Normally the stains used killed the cells
What two innovations in the 20th century led to greater improvements in contrast?
- Phase-contrast microscopy
- Darkfield microscopy
_________________ microscopy makes objects much darker than they would otherwise be, whereas _________________ microscopy shows them as bright objects against a black background.
Phase-constrast microscopy
Darkfield microscopy
What was the most significant advance in microscopy in the 20th century?
The electron microscope
The limit of resolution for an electron microscope is at least a ______________________ times better than the light microscope.
1000 times
Light microscopes cannot visualize objects less than ____ _______. Electron microscopes can theoretically visualize the smallest of objects, but practical issues limit visualization to a _______________ or less.
0.1 µm
1 nm
What did Leeuwenhoek call the microbes moving around in pond water?
Animalcules
For most of human history, people believed that life came from the three processes. What were they?
- Sexual reproduction
- Asexual reproduction
- Spontaneous generation
What is the idea of spontaneous generation?
The supposed production of living organisms from nonliving matter, as inferred from the apparent appearance of life in some supposedly sterile environments.
Who is credited with presenting the concept of spontaneous generation?
Aristotle
Aristotle proposed that life arose from nonliving material if the material contained _______ ______.
Vital heat
_______________ _____________ planted the first seed of doubt regarding spontaneous generation with his “meat and maggot” experiment.
Francisco Redi
How did Redi demonstrate that spontaneous generation was unlikely?
He placed three slices of meat in three containers. The first container was left unopened. The second was corked and sealed. The third was covered with gauze. Maggots developed on top of the meat in the first container. Maggots did not develop on the meat in the second and only developed on top of the gauze in the third. Prior to this, it was believed that meat “spontaneously generated” maggots; Redi’s experiment showed that maggots were the eggs of flies
______________ _________________ “life gravy” experiments challenged Francisco Redi’s “meat and maggots” experiment and supported the idea of spontaneous generation.
John Needham
How did John Needham “prove” the theory of spontaneous generation?
Needham placed a broth, or “gravy,” into a bottle, heated the bottle to kill anything inside, then sealed it. Days later, he reported the presence of life in the broth and announced that life had been created from nonlife
___________________ is the Greek word Aristole used to characterize the “life gravy” or “life force” that causes inanimate objects to come to life.
Pneuma
Who repeated John Needham’s “life gravy” experiment?
Lazzaro Spallanzani
How did Spallanzani identify errors in Needham’s “life gravy” experiments?
He reviewed both Redi’s and Needham’s data and concluded that perhaps Needham’s heating of the bottle did not kill everything inside. He constructed his own experiment by placing broth in two separate bottles, boiling the broth in both bottles, then sealing one bottle by melting its opening and leaving the other open. Days later, the unsealed bottle was teeming with small living things that he could observe more clearly with the newly invented microscope. The sealed bottle showed no signs of life. This certainly excluded spontaneous generation as a viable theory
What three conclusions did Spallanzani make after conducting his experiment?
- Needham did not heat the broth long enough or did not properly seal the bottles
- Microorganisms exist in the air and can contaminate the broth
- Spontaneous generation does not exist, and living things only arise from other living things
Why did critics of the time reject Spallanzani’s conclusions?
Because they believed air was required for spontaneous generation and/or that the heating killed the “life force” required for spontaneous generation to occur
The controversy over spontaneous generation required the development of ____________________ methods.
Sterilization
_________________________’s “swan-necked flask” experiments convinced the scientific community that spontaneous generation was incorrect.
Louis Pasteur
_______________________ discovered that spores were heat resistant and discovered a reliable way to kill them through repeated boiling.
John Tyndall
How did Pasteur provide evidence against spontaneous generation?
Pasteur made a series of flasks with long, twisted necksin which he boiled broth to sterilize it. His design allowed air inside the flasks to be exchanged with air from the outside, but prevented the introduction of any airborne microorganisms, which would get caught in the twists of the flasks’ necks. If a life force were responsible for microbial growth, it would have access to the broth, whereas the microorganisms would not. After several weeks, Pasteur observed that the broth in the straight-neck flask was discolored and cloudy, while the broth in the curved-neck flask had not changed
What theory of disease provided an explanation for the phenomenom of contagion?
The germ theory of disease
What is contagion?
The ability of a disease to pass from one person to another
What disease led to the formulation of the germ theory of disease?
Anthrax
Fermented drinks have been around for a long time. How far back do we have evidence of fermented drinks?
7000 BCE in northern China
Jars of wine estimated to be from ________ BCE werer found in Iran (Babylon); from 3000 BCE in Egypt; from _______ BCE from “Mexico”; and from 1500 BCE from _________.
5000 BCE - Iran
3000 BCE - Egypt
2000 BCE - Mexico
1500 BCE - Sudan
Who determined that yeast is responsible for fermentation?
Louis Pasteur
Be familiar with how Pasteur determined yeast to be the cause of fermentation.
How did Pasteur demonstrate that bacteria did not lead to fermentation?
When Pasteur sealed a flask of juice with bacteria, no alcohol was produced, only acid
How did Pasteur determine that yeast fermented grape juice into wine?
In an experiment, he removed all yeast from grape juice but found that it did not ferment; when he added the yeast back, the grape juice fermented into wine. He suggested that grape juice be heated to destroy all life before fermentation was begun, what we call pasteurization
Why should you not drink wine that has been left open for a week?
Because it becomes vinegar as bacteria colonize the wine and release acids
As early as _______ CE, the idea that microbes caused disease was floating around.
1000 CE
Who finally demonstrated that bacteria caused the disease anthrax and not something else?
Robert Koch
What is the scientific name of the bacteria that causes anthrax?
Bacillus anthracis
Prior to Koch, several people had shown that _________ from a cow with anthrax would cause other cows injected with its blood to die.
Blood
Who was the first to publish photographs of bacteria?
Robert Koch
How did Koch demonstrate that bacteria caused anthrax?
He injected a drop of sheep blood - from a sheep that died from anthrax - into a mouse, and the mouse died within the next day. When he studied blood from the spleen of the mouse, he found the same bacteria present from the sheep blood. Koch ultimately did this 20 times, demonstrating that the bacteria was alive and reproduced while maintaining its pathogenic nature throughout
___________ _______________ techniques were required to show that different diseases were caused by different microbes.
Pure culture technique
Koch’s work with cultures and potato slices, led him to realize that pure cultures required what type of medium in which to grow?
Solid surfaces, not liquid media
A colony is a series of ___________ growths while; each colony - if homogenous - represents a ____ ________.
Localized growths
Pure culture
Why was gelatin a poor substrate for pure culture techniques?
Gelatin melts at the temperature at which most cultures of disease-causing bacteria grow, and gelatin is often broken down as a nutrient by bacteria
What did Koch find to be the best material for pure culture techniques?
Agar
What are three reasons as to why agar is such a useful medium for pure cultures?
- After being melted, agar can remain a liquid until temperatures of less than 50 degrees Celsius (easily pourable)
- After solidifying, it remained so up to 100 degrees celsius
- A derivative of marine algae, it is not normally attacked by bacteria
The Petri dish is named after who?
Julius Petri, an assistant of Koch
What is the streak plate technique used for?
Streak plate technique is used for the isolation into pure culture of the organisms (mostly bacteria), from mixed population. The inoculum is streaked over the agar surface in such a way that it “thins out” the bacteria. Some individual bacterial cells are separated and well spaced from each other. As the original sample is diluted by streaking it over successive quadrants, the number of organisms decreases. Usually by the third or fourth quadrant only a few organisms are transferred which will give discrete colony forming units (CFUs).
Koch’s postulates define what is logically necessary and sufficient to prove the microbial etiology of a disease. What are the four postulates?
- The microbe must be present wherever the disease is present, but absent from healthy organisms
- The microbe must be isolated from the diseased host organism and obtained in pure culture
- The microbe must be inoculated back into a healthy susceptible host, which must becomme ill with the same disease
- The same microbe must be found in the experimentally infected host
- The microbe must be __________ wherever the disease is present, but ____________ from healthy organisms
- The microbe must be ____________ from the diseased host organism and obtained in _____ ____________
- The microbe must be ______________ back into a healthy _____________ host, which must becomme ill with the same disease
- The same microbe must be found in the experimentally infected host
Present, absent
Isolated, pure culture
Inoculated, susceptible
What acronym can be used for the four postulates of Koch’s germ theory?
PIOII
What allows for the isolation of microbes that are present in source material in very low numbers?
Enrichment culture
Who developed enrichment culture?
Martinus Beijerinck
How does enrichment culture work?
A small amount of sample is placed in a liquid medium designed for certain types of organisms; those that grow the fastest increase in proportion to those that grow slowly or not at all; after growth, the resulting population - with its altered ratios - is plated on solid medium, and various different major types are identified
What is the only necessity for performing enrichment culture?
The ability to devise a liquid medium that selectively favors a particular type of organism
What are four microbes that have become model systems for the study of cell biology, molecular genetics, and development?
- Escherichia coli
- Bacillus subtilis
- Caulobacter crescentus
- Saccharomyces cerevisiae
Which model organism is the best studied?
Escherichia coli
Is Escherichia coli gram-positive or gram-negative?
Gram-negative
Which model organism is a bacterial inhabitant of soil and water with a long stalk at one end that is often used to study cell morphology as it divides asymmetrically to produce two different daughter cells?
Caulobacter crescentus
Which model organism is a common soil bacterium that produces a dormant endospore when starved and has been useful in stodying genetics and differentiation?
Bacillus subtilis
Which model organism is a yeast, a unicellular fungus, and the most common eukaroytic microbial experimental system?
Saccharomyces cerevisiae
What organism is this?
Escherichia coli
What organism is pictured?
What organism is pictured?
Bacillus subtilis
What organism is pictured?
Saccharomyces cervisiae
