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Chapter 3 Study Guide- Microbiology
Terms in this set (104)
The Five I's
•Propagation of microorganisms with various media
•Growth of microorganisms in or on a nutrient medium
•A nutrient-containing environment in which microbes can multiply
•Introduction of microbes into or upon media for culture
•Free of all life forms including spores and viruses
•Usual temperatures used in lab: 20 to 45°C
•Incubators also control atmospheric gases such as oxygen and carbon dioxide
•Microbial growth in liquid medium:
•Cloudiness, sediment, scum, color
visible masses of piled-up cells
Media is classified according to three properties:
-functional type (purpose)
•Water-based solutions that do not solidify at temperatures above freezing and flow freely in a tilted container
•Broths, milks, infusions
Exhibits a clot-like consistency at room temperature
Contains enough gelatin or agar to thicken but not produce a firm surface
Used to determine motility of bacteria
Also used to localize a reaction to a specific site
-Provides a firm surface upon which cells can form discrete colonies
-Used to isolate bacteria and fungi
•Solid at room temperature, liquefies at 100°C, and once liquefied, does not begin to solidify until it cools to 42°C
•Any medium containing 1 to 5% agar usually has the word "agar" in its name
Defined (synthetic) media:
media whose chemical compositions are precisely chemically defined
contain some ingredients of unknown composition and/or concentration
General purpose media
grows a broad range of microbes, usually nonsynthetic
contains complex organic substances such as blood, serum, hemoglobin, or special growth factors required by fastidious microbes
Contains one or more agents that inhibit the growth of certain microbes
•Encourage a select microbe to grow
•Important in primary isolation of a certain type of microorganism from a mixed sample
Allow multiple types of microorganisms to grow, but display visible differences between colonies
•Differences in colony size or color, media color changes, or formation of gas bubbles or precipitates
•Variations may be due to metabolism of certain ingredients that cause a color change
Differential Media: Blood Agar
Used as an enrichment medium for fastidious microbes as well as differential media
: enzymes that lyse (break down) red blood cells to release iron-rich hemoglobin
complete lysis of red blood cells
incomplete lysis of red blood cells
Some media can be both selective and differential
Mannitol Salt Agar
grow anaerobic bacteria
Carbohydrate fermentation media
contains sugars and pH indicators to show fermentation
maintains and preserves specimens
used to test the effectiveness of antimicrobial drugs
Used in industrial and environmental microbiology to count the numbers of organisms in milk, water, food, soil, etc.
•A discrete mound of cells formed on solid nutrient surface
•Consists of just one species and no other if formed from a single cell
Requirements of isolation
a small number of cells must be inoculated into a relatively large volume or expansive area of media selected to encourage growth, a relatively firm surface, a petri dish, inoculating tools such as an inoculating loop
Streak plate method
a method of isolating a culture by spreading microorganisms over the surface of a solid culture medium
Pour plate method
A method of inoculating a solid nutrient medium by mixing bacteria in the melted medium and pouring the medium into a Petri dish to solidify
Spread Plate Technique
A small volume of sample is pipetted onto the surface of the plate
A sterile spreading tool or "hockey stick" is used to spread the sample around evenly on the surface to form individual colonies
contains only one species or strain
free of other living things except for the one being studied
a second-level culture from a well-isolated colony
A container growing two or more different, known species of microbes.
A culture that was once pure or mixed that now contains contaminants, or unwanted microbes of uncertain identity
Microbial profiles are determined through combining:
Biochemical tests can determine fundamental chemical characteristics such as:
•Products given off during growth
•Presence of enzymes
Mechanisms for deriving energy
detects microbes based on their DNA
testing the isolate against known antibodies
Dimensions of microscopic organisms are measured from millimeters (mm) to micrometers (μm) to nanometers (nm)
•Viruses: 20 to 800 nm
•Smallest bacteria: 200 nm
•Yeasts: 3 to 4 μm
•Protozoa: 50 to 100 μm
the bending of a wave as it enters a new medium at an angle
Formation of an Image
occurs when an object is placed at a certain distance from the spherical lens and illuminated with light
Simple magnifying lens and a few working parts
Later compound microscopes
- Second magnifying lens
- Lamp in the base to illuminate the specimen
- Condenser used to focus light onto the specimen
Three properties of an effective microscope:
magnification, resolution, contrast
Eyepiece of a microscope
The capacity of an optical system to distinguish or separate two adjacent objects or points from one another
a measure of the clarity of an image
Oil Immersion Lens
100x objective lens
a measure of how greatly a substance slows the velocity of light
Four types of light microscopes:
bright-field, dark-field, phase-contrast, fluorescence
uses ultraviolet radiation as the illuminating source
uses a laser beam as the illuminating source
The method of specimen preparation depends on:
the condition of the specimen (living or preserved), The aims of the observer: observation, identification, movement, and the type of microscopy available
Consist of a drop or two of culture placed on a slide overlaid with a coverslip
Advantages of wet mount
quick and easy to prepare
Disadvantages of wet mount
•Can damage larger cells
•Susceptible to drying
•Can contaminate the handler's fingers
Hanging drop mount
Uses a depression slide, Vaseline, and coverslip
The sample is suspended from the coverslip
- Spread a thin film made from a liquid suspension of cells on a slide
- Allow the slide to air dry
- Heat fixing
• Heat the slide gently after it has been air dried
•Heat the slide gently after it has been air dried
Important functions of heat fixing
-Kills the cells
-Secures the specimen to the slide
-Preserves cellular components in a natural state with minimal distortion
Makes inconspicuous features stand out
Dyes impart colors to cells by becoming affixed to them through a chemical reaction
Dyes used in microbial staining:
Positively charged stain is attracted to negatively charged cell walls
Stick to the cell and give it color
•Negatively charged dye is repelled by negatively charged bacterial cell walls
•Produces a black background around the cells
one dye is used; reveals shape, size, and arrangement
Use two differently colored stains to clearly contrast cell types or cell parts
Types of complex staining techniques
A staining method that distinguishes between two different kinds of bacterial cell walls.
a differential stain used to identify bacteria that are not decolorized by acid-alcohol
is applicable to only a few groups of bacteria AND usually shows the spores as green structures among a background of pink cells.
Used to emphasize certain cell parts that may not be revealed by conventional staining methods
•An unstructured protective layer surrounding the cells of some bacteria and fungi
whiplike tails found in one-celled organisms to aid in movement
-Flagella must be enlarged in order to be seen
-A coating is deposited on the outside of the filament and then stained
The correct microbiological term for the sample of specimen that is put into a nutrient medium to produce a culture is ______.
A reducing medium contains _______.
substances that remove oxygen
What is the term for a culture made from one isolated colony?
both anexic and pure
Newly inoculated cultures must be _____ at a specific temperature and time to encourage growth.
The Five I's of studying microorganisms include all of the following except ______.
The bacterium Neisseria gonorrhoeae causes the sexually-transmitted infection gonorrhea. Although it can be isolated from the vagina, there are numerous normal biota in that location as well. To generate a pure culture of this pathogenic bacterium, the best choice is a/an ______.
The term that refers to the purposeful addition of microorganisms into a laboratory nutrient medium is ______.
Which of the following is produced by adding 1% to 5% agar to nutrient broth that is then boiled and cooled?
A microbiologist must culture a patient's feces for intestinal pathogens. Which of the following components would likely be present in a selective medium for this purpose?
A microbiology student with a visual disability is viewing a sample of Bacillus endospores in a phase contrast microscope that is linked to an iPad. By "stretching" the image on the iPad screen, the student can increase the apparent size of the endospores. How does this manipulation affect resolution and contrast? (No software is being used to alter the image!)
Only the magnification can be increased; resolution and contrast are unchanged.
The simple microscopes used by the earliest practitioners of microscopy contained which of the following?
Which type of microscopy transforms the subtle variations in cell density into differences in light intensity, allowing for increased internal detail without staining?
All of the following are diameters of cells that would be resolved in a microscope with a limit of resolution of 0.2 µm except ______.
Humans can see objects as small as 0.1 mm. Leeuwenhoek's best microscope could magnify objects to 300X. Which of the following would be invisible using Leeuwenhoek's microscope?
Which type of microscope cannot image live specimens?
Magnification is achieved in a compound microscope through the initial magnification of the specimen by the _____ lens. This image is then projected to the _____ lens that will further magnify the specimen to form a virtual image received by the eye.
Scattering of peripheral light rays through the glass slide under very high magnification can be prevented by ______.
Which term refers to the microscope's ability to show two separate objects as discrete and distinct?
The type of microscopy in which you would observe brightly illuminated specimens against a black background is ______.
The _____ of the microscope holds and allows selection of the objective lenses.
Which type of microscope bombards a whole, metal-coated specimen with electrons moving back and forth over it?
A textbook uses Paramecium to illustrate several types of light microscopy. Each image is magnified 230X and measures about 4 cm. The actual size of a Paramecium is about ______.
The purpose of staining cells on a microscope slide is to ______.
add contrast to see them better
A microbiologist makes a fixed smear of bacterial cells and stains it with methylene blue. All cells appear blue under the oil immersion lens. This is an example of ______.
The specimen preparation technique that is best for viewing cell motility is the ________.
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