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Final Lab Exam
Terms in this set (85)
Viable organisms refer to what types of microorganisms?
1. All organisms present in the sample
2. All living organisms present in the sample
3. Only those organisms capable of producing disease - pathogens
4. Only those organisms capable of producing disease in immunocompromised individuals
All living organisms present in the sample
If a 1ml sample was diluted in 100ml of sterile diluent and 1ml of that dilution was then tested and found to contain 40 cfu, what was the amount of bacteria present in the original 1ml sample?
1. 40 ctu/ml
2. 4 ctu/ml
3. 400 cfu/ml
4. 4000 cfu/ml
Why is ground beef (hamburger) contain more bacteria than a steak or roast?
Ground beef is all surface so the bacteria is spread throughout. Steak only contains bacteria on the outside.
What is the indicator organism tested for in water, which indicates whether or not there is fecal contamination present?
The definition of resolution in microscopy or any optical system is:
1. The ability to magnify or enlarge the specimen
2. The ability to enhance the contrast of the specimen so that the specimen or parts of the specimen are easier to see in relation to the background
3. The shortest distance between 2 points on a specimen that can still be distinguished as separate entities
4. The concentration of light allowing for very small specimens to be illuminated
The shortest distance between 2 points on a specimen that can still be distinguished as separate entities
Parfocalization refers to what aspect of the microscope?
1. The fact that most any size object can be focused properly
2. Focusing requires the use of the fine focus knob to properly view the specimen
3. The fact that when one lens is in focus, all the other lenses should be in approximate focus and should only require minor adjustments for clarity
The fact that when one lens is in focus, all the other lenses should be in approximate focus and should only require minor adjustments for clarity
If the objective lens is labeled as 12X and the ocular or eyepiece lens is labeled as 10X, then the total magnification would be?
Which type of microscopy has the best resolution?
1. Brightfield using violet light
2. Brightfield using red light
3. Electron microscopy
4. Phase Contrast microscopy
What are the 2 methods for observing live microbiological specimens called?
1. Smear and wet mount
2. Hanging drop and smear method
3. Depression slide mount and wet mount
4. Wet mount and hanging drop
Wet mount and hanging drop
Why are living organisms, difficult to see with a regular brightfield microscope?
1. Living organisms have an approximate water content of 70% and therefore their refractive index is very similar to the media they are suspended in, making them appear as shadows
2. They are too small to visualize with a brightfield microscope
3. Living organisms have no cell walls only plasma membranes and therefore they are constantly changing shape and size
4. Living organisms, especially bacteria, are very easy to visualize with a brightfield microscope
Living organisms have an approximate water content of 70% and therefore their refractive index is very similar to the media they are suspended in, making them appear as shadows
What is Brownian motion?
Since bacteria move with flagella, how do their movements differ from Eukaryotic cells that move with flagella?
1. Bacteria move by flagella undulating and therefore smoothly glide through the medium, whereas Eukaryotic organisms move by flagella rotating and when changing directions have erratic motion
2. Bacteria move by flagella rotating and therefore when changing direction have erratic motion, whereas Eukaryotic organisms move by flagella undulating and smoothly glide through the medium
3. There really is no difference between the movement of bacteria and the movement of Eukaryotic organisms, if both have flagella
4. There really is no difference between the movement of bacteria and the movement of Eukaryotic organisms, if both have flagella, the erratic motion occurs if there is cilia instead of flagella
Bacteria move by flagella rotating and therefore when changing direction have erratic motion, whereas Eukaryotic organisms move by flagella undulating and smoothly glide through the medium
After preparing a smear of bacteria on a slide, why do you heat fix the specimen?
1. Fixing adheres the specimen to the slide
2. Fixing kills the bacteria
3. Fixing denatures bacteria proteins allowing for bacteria to take up stain and be viewed close to true size and shape
4. All of the above
All of the above
Most microbiological stains are basic stains with a positively charged chromophore (cation). This chromophore does what to the bacterial smear?
1. It is attracted to the negatively charged bacteria and stains the bacteria
2. It is repelled by the positively charged bacteria but slightly attracted to the glass slide, slightly staining the slide but not the bacteria
3. It is attracted to the negatively charged cell wall of the bacteria and only stains the cell wall
4. It is attracted to the negatively charged nucleus of the bacteria and only stains the cell nucleus
5. Basic stains are not used in microbiology
It is attracted to the negatively charged bacteria and stains the bacteria
A bacterial smear from an agar colony (solid media) is made by:
1. Aseptically transferring a loop of bacteria from the colony and rubbing all over glass slide-air dry-heat fix
2. Aseptically transferring a loop of bacteria from the colony and mixing in a tube of sterile water and then transferring a loop of this suspension to a slide-air dry-heat fix
3. Placing a loop of water on a slide, transferring another loop of bacteria (large amount) and mixing it in water-air dry-heat fix
4. Placing a loop of water on a slide, transferring another loop of bacteria (very very small amount) and mixing it in water-air dry-heat fix
Placing a loop of water on a slide, transferring another loop of bacteria (very very small amount) and mixing it in water-air dry-heat fix
The value of the simple stain lies in the ability of the scientist to be able to view the microorganism by increasing the refractive index of the microorganism compared to the environment of the specimen:
Bacteria may be divided into two categories (gram positive and gram negative), which are differentiated from each other by what bacterial structure?
1. Cell wall
4. Plasma membrane
If the gram stain procedure was stopped after the iodine step and the preparation was then observed under the microscope, gram negative organisms would appear as:
When completing the Gram Stain, dead bacteria cells or cells that are old will stain what color?
What is applied to the organism during the differential step in the gram stain?
3. Crystal Violet
Agar is a solidifying agent made from algae, which liquefies at what temperature?
1. 100° C
2. 42° C
3. 25° C
4. 37° C
Agar in a liquid state, solidifies at what temperature (approximately)?
1. 100° C
2. 40° C
3. 70° C
4. 0° C
Fermentation is a metabolic process that occurs in what conditions?
1. High salt concentrations
2. Very high Oxygen concentrations
3. Low to zero Oxygen concentrations
4. High acid concentrations
Low to zero Oxygen concentrations
What is the purpose of fermentation?
1. To create a lot of ATP (energy)
2. To create NAD+
3. To create alcohol
4. To create lactic acid
To create NAD+
RODAC plates are agar plates having a convex surface, which allows you to contact a flat surface and extract the surface microorganisms. RODAC is an acronym for:
1. Red organisms determined to actually count
2. Round organisms detected and counted
3. Replicate organism detection and counting
4. Real organisms determined and counted
Replicate organism detection and counting
After incubating inoculated plates, arising colonies are counted and listed as the number of CFU's/area. The designation FU stands for:
Colony forming units
In environmental sampling, the purpose of using plate counts (Swab testing) is to determine what?
1. All microorganisms present (dead or alive)
2. Bacteria only
3. Only viable microorganisms
4. Pathogenic microorganisms
Only viable microorganisms
Aseptic techniques are procedures used in microbiology to:
1. Exclude contaminants from the testing
2. Introduce organisms into the procedures
3. Techniques to kill or inhibit microorganisms
4. None of the above
Exclude contaminants from the testing
What type of microbiological medias are MacConkey and Mannitol Salt?
4. Chemically defined
5. Both 1 and 2
Both 1 and 2
Bile salts in MacConkey agar, allow only gram negative organisms to grow. Neutral red present in the MacConkey agar, detects a pH drop when what carbohydrate is fermented to lactic acid?
In Mannitol Salt agar, the selective agent is 7.5% saline, which allows for what group of organisms to grow?
One of the waste products of aerobic metabolism is hydrogen peroxide (H2O2). This waste product will kill the cell unless it is neutralized. What is the enzyme produced by our cells and Staphylococcus spp. which
will neutralize hydrogen peroxide (2H202———> 2H20 + 02)?
What group of bacteria is responsible for pharyngitis or strep throat?
1. Alpha hemolytic streptococci
2. Beta hemolytic streptococci
3. Gamma hemolytic streptococci
4. Group A Beta hemolytic streptococci
Group A Beta hemolytic streptococci
Blood agar is what type of media?
3. Selective & Differential
4. Chemically Defined
Organisms recovered from both a nasal swab and an underarm axillae swab grew on Mannitol Salt Agar and exhibited a yellow area around the colonies. These organisms were most likely?
1. Staphylococcus aureus
2. Staphylococcus epidermidis
3. Staphylococcus albus
4. Streptococcus pyogenes
According to most studies, 80% of people carry Staphylococcus aureus in their nasal passages?
ocular lens x objective lens
-Shortest distance between 2 points that can still be distinguished as separate
-eye: 0.2 mm
-microscope: 0.2 Mm
when 1 lens is in focus, all lenses are in focus with minor adjustments
1 mm= ?
3 ways to adjust light
2. condenser diaphram
3. light source diaphragm
objective lens, specimen, condensor, light source, ocular lens, stage, course adjustment, fine adjustment
3- objective lens
8- light source
9- ocular lens
12- course adjustment
13- fine adjustment
Psuedopods, cilia, flagella (whiplike, smooth motion)
Flagella rotate clockwise, erratic
false movement, vibration caused by h20
live organisms hard to see, 70% water
Why does a simple stain increase refractive index
Principles of staining
-stains are salts
-bacteria have a slight negative charge, environment has a slight positive charge
Preparing a smear
1. transfer a loop of water to slide w/ sterile loop
2. sterilize loop
3. transfer a smidgen of bacteria to water and spread out on slide
4. let air dry
5. heat fix
6. cool and stain (1 min of stain, wash, blot)
large ion to see color
differential stain based on cell wall
purple, thick peptidoglycan layer
red, thin layer
Preparing a gram stain
1. Initial stain (crystal violet, 1 min)
2. Mordant (iodine, 1 min)
3. Differential step (alcohol, 5 seconds, decolorizer)
4. Counter stain (sanfrain, 1 min)
Gram stain dead bacteria
Gram stain too much bacteria
Gram stain too much alcohol
Gram stain too little alcohol
Temp for agar to liquify
100 degrees C
Temp for agar to become solid
40 degrees C
eat nutrients, not agar
isolation/purity (surface area)
motility (semi-solid, bacteria can move)
occurs at little to no O2, recycles NAD so glycolysis can continue
Colony forming units
too numerous to count
less than or equal to 1 cfu
Mannitol salt agar
-selective and differential
-selective: halodures (high salt)
-differential: mannitol fermentation (acid)
-S. aur and S. epidermis
-selective and differential
-selective: gram negative
-differential: lactose fermentation
-S. aur, E. coli, Salm
-differential: starch hydrolysis (amylase)
-s. aur and bacillus
-oxidase: cytochrone oxidase
-80% infections passed via contact
-media: mannitol salt
-30% carry s. aureus in nose
-10-20% carry strep pyrogens in throat
count X dilution
metallic green= ecoli
-kirby bauer test
zones of inhibition (in mm diameter)
-first sign of now growth is time to kill 99%
-same as derby Bauers with no table
-best= most effective
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