57 terms

Microbiology Midterm

Midterm study guide for online Microbiology at SPC
Name the parts of the microscope and their functions
The head or body of a compound microscope contains the optical parts of the microscope.
The base of a compound microscope is helps in supporting the microscope and contains the illuminator.
The arm acts as a connector between the base and the head of the compound microscope.
The eyepiece is the ocular lens that helps you look through to see a magnified image from the top of the microscope. The lens have a power of magnification of about 10x or 15x.
Eyepiece Tube:
The part that connects the eyepiece with the objective lens is the tube.
Objective Lens:
You can see three or four objective lens attached to the end of the tube. The lenses range from 4x to 100x magnifying powers. To make matters simple, you can identify the longest objective lens as the one that provides the highest magnification power. The shortest objective lens is the one that provides minimum magnification power.
Rack Stop:
It is a factory set adjustment that determines how close the objective lens can get to the slide. This prevents the viewer from cranking the high power objective lens into the slide. It is used only when really thin slides are used to focus a sample under high power.
The nose piece that supports the objective lens is known as turret or revolving nosepiece. You can rotate the turret and change the power magnifications as per requirement.
Coarse and Fine Focus:
These are the knobs that help focus the microscope. There are many compound microscopes that have coaxial knobs. The coaxial knobs are built on the same axis as the fine focus knob on the outside. This proves to be more convenient to use as you do not need to fumble with different knobs.
The stage is the flat surface on which you keep the specimen to be observed. Microscopes with mechanical stage have two knobs. These knobs can be used to move the slide around, that is, left and right or up and down.
Stage Clips: The stage clips are used to hold the slide in place on the stage.
The tiny hole in the stage that helps in transmitting base light to the stage.
The light source that is located at the base of the microscope. The mirror reflects the light from the outside source through the bottom of the stage. This helps in illuminating the sample on the slide. Many light microscopes use low voltage halogen bulbs. They have a continuous variable light control part at the base that helps in focusing in different light range.
The condenser is present at the base of the stage. It is usually connected to the iris diaphragm.
Iris Diaphragm:
This part helps in controlling the amount of light that reaches the specimen. The diaphragm is located above the condenser and below the stage.
Condenser Focus Knob:
In order to help the condenser move up and down and control the lighting focus on the specimen, a condenser focus knob is used.
numerical aperture
The characteristic of a lens which determines the amount of light that enters the lens. The higher the numerical aperture, the smaller the minimum resolvable distance and the better the resolution
The process of using an embedded micrometer
image brightness
Magnification range of different types of microscopes
which microscope uses ultraviolet light?
Flourescent Microscope
What type of microscopy allows one to see internal structures of cells in a natural state?
Phase Contrast Microscope
the increase of an object's apparent size by using lenses or mirrors
the ability of a microscope or telescope to measure the angular separation of images that are close together
How long is a micron?
1 micrometer or 0.0001 millimeters
how do different types of cells measure in microns
Most bacteria are 0.2 um in diameter and 2-8 um in length
How are different bacterial cell shapes and arrangements described?
the three basic bacterial shapes are coccus (spherical), bacillus (rod-shaped), and spiral (twisted)
How do you identify bacterial shapes and arrangements
the three basic bacterial shapes are coccus (spherical), bacillus (rod-shaped), and spiral (twisted)
Difference between gram positive and gram negative
Gram positive, retain stain when washed with alcohol. Gram negative, those that are decolorized by the alcohol wash.
What does fixing cells on a slide do
denatures any enzymes that might lyse the cells or interfere with the staining procedure.
it also kills the organism and adheres the organism to the slide for staining
When is negative staining used and what does it tell you
To determine numbers, size, shape, and arrangement
Difference between acidic and basic stains
An acidic stain has a negatively charged chromogen and a basic stain has a positively charged chromogen
Aseptic technique
steps necessary to ensure an environment free from pathogens
What does a microorganism need to grow and how do the factors affect growth
F ood
A cidity
T emperature
T ime
O xygen
M oisture
How do you control microbial growth using heat, cold, chemicals, etc
How are the factors that affect microbial growth used to control it
Difference between chemically defined and complex media
In the complex media you have unknow compounds mixed in wheras; in the defined media you know all concentrations of the compounds in the media
Reducing Media
contain ingredients that chemically combine with O2 and are heated to kill off O2, growth of obligate anaerobes
Differential Media
formulated so that either visible changes or differences in the medium or colonies can help differentiate among the kinds of bacteria growing.
selective media
suppress growth of unwanted bacteria and encourage growth of desired microbes
enrichment media
contains special nutrients that encourage growth of particular microbes but do not inhibit others
nutrient agar
-solid medium containing beef extract and peptone, and agar.
how are microorganisms classified based upon their temperature requirements
Psychrophiles grow in subfreezing (1 °C) to above freezing temperatures (4-25 °C), mesophiles
(25-37 °C), and thermophiles (above 40 °C)
Direct count
A method of measuring bacterial growth by counting cells in a known volume of medium that fills a specially calibrated counting chamber of a microscope slide
indirect count
(Spectroscopy) This is the estimated number of all cells including dead or inactive cells by measuring the amount of light that passes through a liquid culture using a spectrophotometer (cells/mL).
Viable count
an approximation of the number of living organisms per unit volume based on the formation of colonies on a solid growth media
Total count
a test sample which determines the total number of that cell type per unit volume; both living and dead cells
Why would one want to isolate individual colonies?
Individual colonies in a mixed growth are hopefully composed of all of one type of microbe. Having one microbe in a sample makes it possible to identify it. The tests to help determine between different microbes are not effective as they could give you mixed responses and cause you to eliminate all possibilities
Different methods used for isolation of colonies and when each is applicable
1 The Spread Plate: If a mixture of cells is spread out on an agar surface so that every cell grows into a completely separate colony, a macroscopically visible growth or cluster of microorganisms on a solid medium, each colony represents a pure culture. The spread plate is an easy, direct way of achieving this
2 The Pour Plate: Extensively used with bacteria and fungi, a pour plate also can yield isolated colonies. The original sample is diluted several times to reduce the microbial population sufficiently to obtain separate colonies when plating result.
3 The streak plate: Pure colonies also can be obtained from streak plates. The microbial mixture is transferred to the edge of an agar plate with an inoculating loop or swab and then streaked out over the surface in several patterns
Compare isolation methods
When is each type of culture media used
How do you determine the number of bacteria in a sample by dilution and viable plate counts? What other methods are used to measure bacterial growth?
Purpose of differential staining and how it's achieved
gram stain
Differential staining procedure that allows categorization of bacteria into two groups (gram-positive and gram-negative) based on their ability to retain crystal violet when decolorized with an organic solvent such as ethanol.
endospore stain
a differential stain used to detect the presence and location of spores in bacterial cells.
flagellar stain
Staining that allows bacterial flagella to become visible; allows determination of number and location of bacterial flagella
capsule stain
A differential stain used to detect cells capable of producing an extracellular capsule. The acidic stain colorizes the background while the basic stain colorizes the cell, leaving the capsules as unstained, white clearings around the cells. Under a microscope you can see that they lack uniform capsule size and even the absence of a capsule in some cells.
Acid fast stain
a differential stain technique that identifies bacterial that have a waxy material in their cell walls; uses Carbolfuchsin as its primary stain, Acid-alcohol as its decolorant, Methylene blue as its secondary stain. Used for mycobacterium Tuberculosis
steps of gram stain
1)crystal violet (primary dye) 2)Gram's iodine (mordent - binds together) 3)Alcohol (decolorize - removes excess) 4)Safranin (Red dye counterstain)
What does mordant in the gram stain do
iodine added to enhance crystal violet staining by forming a crystal violet-iodine complex
Difference between gram stain and acid-fast stain
Provides a contrasting stain to the primary stain. Safranin, stains the Gram-negative bacteria pink to red
teichoic acids
part of the gram positive cell wall that is connected to cytoplasmic membrane
Difference between gram positive and gram negative cell walls
Gram + cell wall is much thicker peptidoglycan layer, lacks the cell envelope, and contains additional substances, such as teichoic acids, polymers composed of glycerol or ribitol.

Gram- bacteria are generally more sensitive to growth inhibition by dyes, small peptidoglycan layer sandwiched between lipoproteins
MR VP test
This test is used to determine two things. The MR portion (methyl red) is used to determine if glucose can be converted to acidic products like lactate, acetate, and formate. The VP portion is used to determine if glucose can be converted to acetoin.
How are MR and VP tests performed? Which reagents are used?
How are MR VP test results interpreted
Which end products are you testing for in MR and VP tests
How is Glucose fermentation detected
How are gas and acid production detected
How do catalase and superoxide dismutase protect bacteria
How do you detect catalase production? What does this enzyme act on?