d) all of these
Differential staining allows one to:
a) identify pathogenic vs nonpathogenic bacteria
b) distinguish b/w eukaryotic and prokaryotic cells
c) identify various bacterial types based on color
d) all of these
b) positive
In differential staining, the cells retaining the first or primary stain are usually termed:
a) fast
b) positive
c) resistant
d) simple
b) they resist penetration of an alcohol/HCI solution into their cells
The reason why certain bacteria are termed "acid-fast" is:
a) they release HCI from their cell walls
b) they resist penetration of an alcohol/HCI solution into their cells
c) they require a low pH to grow
d) they use acid to dissolve needed nutrients
c) crystal voilet/iodine
Peptidoglycan and teichoic acid form a molecular complex with:
a) safranin
b) carbol fushin
c) crystal voilet/iodine
d) methylene blue
c) acid-fast
A cell is first stained with carbol fuchsin, decolorized, and then exposed to methylene blue. When observed under the microscope, the cells exhibit a blue color. This indicates that these cells are:
a) Gram-positive
b) Gram-negative
c) acid-fast
d) nonaci
> red (from safranin dye counterstain)
___ is the color of Gram-negative staining reaction under the microscope
> green (from brilliant green dye counterstain)
> blue (from methylene blue dye counterstain)
> red (from safranin dye counterstain)
> violet (from crystal violet dye primary stain)
> acid-alcohol
___ is a chemical used as a decolorizer in the ACID-FAST stain
> safranin
> alcohol
>differential
> acid-alcohol
> violet (from crystal violet dye primary stain)
___ is the color of Gram-positive staining reaction under the microscope.
> green (from brilliant green dye counterstain)
> blue (from methylene blue dye counterstain)
> red (from safranin dye counterstain)
> violet (from crystal violet dye primary stain)
> differential
___ is the type of stain where various types of microbes can be identified based on color
> simple
> differential
> blue (from methylene blue dye counterstain)
___ is the color of ACID-FAST staining reaction under the microscope.
[Note that brilliant green dye is the
alternative
counterstain for the dye used to produce this color reaction]
> green (from brilliant green dye counterstain)
> blue (from methylene bl
c) acid-fast stain
The stain used to visualize Mycobacteria is:
a) simple stain
b) Gram stain
c) acid-fast stain
d) endospore stain
d) all of these
A normally Gram-positive cell shows up as Gram-variable. Which explanation reveals why this occurred?
a) the smear was too thick
b) the smear was exposed to the decolorizer too long
c) a 48-hour culture was used
d) all of these
b) violet
What color would Gram-positive cells show under the microscope?
a) pink
b) violet
c) blue
d) green
d) retains the color of the primary stain
A microbial cell that shows up positive in a differential stain:
a) is impermeable to water
b) has a thick cell wall
c) has been decolorized
d) retains the color of the primary stain
b) teichoic acid
The chemical found in Gram-positive cell walls not in Gram-negative cell walls that reacts w/the crystal violet-iodine complex is:
a) lipopolysaccharides
b) teichoic acid
c) protein coat
d) peptidoglycan
d) as a fixative or mordant
The iodine in the Gram stain is used:
a) to remove safranin from the cell wall
b) to decolorize
c) as a primary stain
d) as a fixative or mordant
b) safranin
Which stain is used as the counterstain for the Gram stain?
a) iodine
b) safranin
c) cystal violet
d) methylene blue
Alcohol
chemical used to decolorize the Gram stain
To cultivate microorganisms we must provide them with
nutrients such as proteins, carbs, minerals, vitamins, and moisture in the right composition.
colony
a visible aggregate of cells that is formed from a single bacteria cell deposited of a certain area on an agar plate that multiplies at the site.
what is the purpose of quadrant streaking
-for isolation colonies
what is the purpose of gram stain
-Gram positive, and gram negative.
-gram pos look like a dark blue/purple colour, and gram neg look red
A mixture of nutrients such as proteins, carbs, minerals, vitamins, and moisture in the right composition is called?
-culture medium (plural, media). it may be prepared in liquid form, as a broth or solidified with agar.
nonnutritive solidifying agent extracted from?
-seaweed.
solid media are essential for
-isolating and separating bacteria growing together in a specimen collected from a patient; for example, urine or sputum.
In order to study the properties of individual species without interference from other species, the microbiologist must work with-
-single colony, pure cultures.
why streaking plates to obtain pure cultures is critical?
-it allows the microbiologist to determine how many types of bacteria are present, which are causing the disease, and test which antimicrobial agents will be effective for treatment.
colonial morphology
appearance of colonial growth on agar media such as color, density, consistency, surface texture, shape, and size.
Growth layered at the top, center, or bottom of a broth tube reveals?
-organisms' oxygen requirements.
The best bacterial stains are?
-aniline dyes( synthetic organic dyes made from coal-tar products).
The aniline dyes react in
-either an acidic, basic, or neutral manner. acidic and basic are used primarily in bacteriologic work.
The free ions of acidic dyes are
-anions(negatively charged) that combines with cations of a base in the stained cell to form a salt.
The basic dyes possess
-cations(positively charged) that combine with and acid in the stained material to form a salt.
Bacterial cells are rich in what? and stain very well in what dyes?
-rich in RNA(contained in their abundant ribosomes) and stain well in basic.
Neutral stains are made by combining acidic and basic dyes which are most useful for staining?
-complex cells of higher forms because they permit differentiation of interior structures, some which are basic and other are acidic.
Stained bacteria can be measured for what? and classified by their?
-measured for size and classified by their shapes and groupings.
bacteria have rigid cell walls and maintain a constant shape that is used as
-basis for their classification.
what are the bacteria three basic shapes?
-spherical(coccus, plural cocci).
-rod(bacillus, plural bacilli)
-spiraled(spirillum plural spirilla)
Long sinuous organisms with many loose or tight coils with flexible bodies are called?
-spirochetes
-Diplococci
-pairs
Strepto-
-chains
Staphylo-
grapelike, clusters
Tetrads
-packet of four
Palisades
-V, X, Y forms, clubbing
Endospore-forming
-small, round hollow bodies in cell
Pleomorphism
-varying widths and lengths
Spirilla
-short, curved, or spiral forms with rigid bodies.
The simplest method for examining living microorganisms is to
-suspend them in a fluid( water, saline, or broth) and prepare a "wet mount.
The method of suspending bacteria with fluid is used to determine whether an organism
-is motile, but also permits an undistorted( untwisted) view of natural cell groupings and of individual cell size and shape.
Brownian movement?
-small particles of any kind, including bacteria (whether motile or not), are constantly bombarded by the vibration of the fluid molecules, and so are bobbed up and down, back and forth.
True motility
-movement caused by currents in liquid. if a wet mount contains bubbles, air currents set up reacting fluid currents.
Compare wet mount and stained preparation?
-stained preparation is good for studying morphology but not motility because bacteria are already killed.
-wet mount is good for studying bacteria motility.
What reason do we need to stain bacteria?
1) - stains make microbes stand out against the background.
2) - helps investigators group major categories
3) - helps to distinguish parts of a cell.
Why is a blood agar plates used for the growing culture from the mouth rather than nutrient agar?
Some organisms have complex nutritional requirements that is not easily mimicked with nutrient agar. Using blood agar will allow them to grow better.
Why is macconkey agar selective as well as differential?
MacConkey agar
1. Selective media
- bile salts to support the growth of Gram negative microbes
- crystal violet to inhibit the growth of Gram positive microbes
2. Differential media
- neutral red indicator as visual response
What is the difference between Modified Thayer-Martin MTM agar and Chocolate Agar? When would you use MTM?
Chocolate agar is essentially blood agar that contains lysed red cells and a couple of growth-promoting agents to grow organisms of Hemophilus and Neisseria. MTM is essentially chocolate agar, but it contains inhibitory agents that are more selective for
if you wanted to isolate s. aureus from a pus specimen containing a mixed flora, what medium would you choose to get the results most rapidly?
EMB agar - Inhibits other organisms due to the presence of methylene blue dye
MacConkey agar - Inhibits other organisms due to the presence of crystal violet dye
Mannitol salt agar (MSA) - High salt concentration does not allow other organisms to grow onl
an iodine solution is used as a
-mordant (a chemical that fixes a dye in or on a substance by combining with the dye to form an isoluble compound) for the first crystal violet stain.
Gram positive cell walls are composed of:
- Thick, tightly linked peptidoglycans (protein-sugar complexes) in which the crystal violet iodine complex becomes trapped, thereby enabling the cells to resist decolorization.
Gram negative bacterial walls have high concentration of
-lipids (fats) in their outer membranes. the lipids dissolve in the decolorizer (alcohol, acetone, or a mixture) and are washed away along with the crystal violet-iodine complex.
Gram stained smears are read promptly to determine the
-relative numbers and morphology of bacterial in the specimen.
-this information is valuable to the physician in planning the patients treatment before the specimen.
The numerous modifications of Gram's orginal method are based on
-the concentration of the dyes, length of staining time for each dye, and composition of the decolorizer.
What is the lowest and fastest decolorizers?
-ethyl alcohol slowest which permit the student to gain experience with decolorization.
-Acetone is the fastest with an equal mixture of 95% ethyl alcohol.
-the most popular is the combination of acetone-alcohol.
An organism's appropriate Gram-stain reaction depends on the presence of?
-an intact cell wall.
What makes the gram-positive of crystal violet-iodine complex appear falsely gram-negative or mixture?
-when bacteria culture age and wall begins to disintegrate.
Can you distinguish between various organisms on the basis of color alone, not shape?
- you CANNOT distinguish between Staphylococcus (positive/purple) and Streptococcus (positive/purple)
- you CAN distinguish between Staphylococcus (positive/purple) and Neisseria (negative/red)
- you CANNOT distinguish between Escherichia (negative/red) a
how does iodine has an affect on staining?
The iodine in Gram stain fixes the crystal violet to the bacterial cell wall of the Gram positive bacteria.
what is the purpose of the alcohol solution in the gram stain?
The alcohol serves to dehydrate the peptitoglycan layer of the cell wall. Because it is the outermost layer of the Gram positive bacterial cell wall, it is dehydrated by the alcohol. This causes pores to shut in the crystal violet, staining it purple. The
What kind of clinical situation would a direct smear report from the laboratory be of urgent importance?
-Cervical smear - test for cancer
-a thick blood smear for malaria disease,
viability of sperm cells from semen
What 2 conditions may cause gram variable staining (both positive and negative reactions)?
1. bad staining technique
2. bacteria with cell walls particularly sensitive to breakage during cell division, resulting in Gram-negative staining of Gram-positive cells
Acid fast stain
a glass slide, stained, and heated. The cells in the sample hold onto the dye. The lab team member washes the slide with an acid solution and applies a different stain.
The bacteria that hold onto the first dye are considered "acid-fast" because they resi
Examples of Differential Stains?
A differential stain is used to distinguish between two different organisms. It is used to see a difference in the elements of a cell. A couple of examples of differential stains are acid fast and gram stain.
saprophytic mycobacteria
-Mycobacterium species are found in the environment and are rarely pathogenic or have not yet been associated with infection.
What is special about Mycobacterium and staining
-contain large amount of lipid substances within their cell walls. These fatty waxes also known as mycolic acids, resist staining by ordinary methods.
What happen to cell wall when applying basic dye such as carbolfuchsin with heat or in concentration solution.
-stain can penetrate the lipid cell wall and reach the cell cytoplasm. once the cytoplasm is stained, it resist decolorization, even with harsh agents such as acid-alcohol.
what is non-acid fast
-Other bacteria whose cell walls do not contain high concentrations of lipids are readily decolorized by acid-alcohol after staining with carbolfuchsin.
Why isn't the Gram stain used on acid-fast bacteria?
Acid fast bacteria are not classified as either Gram-positive or Gram-negative because they do not have the chemical characteristics of either, although the bacteria do contain peptidoglycan (murein) in their cell wall. If a Gram stain is performed on Myc
When you have an infection, you should request an acid-fast strain. The test can tell if you have come into contact with the bacteria that causes tuberculosis and related infections.
When you have an infection, you should request an acid-fast strain. The test can tell if you have come into contact with the bacteria that causes tuberculosis and related infections.
Does the presence of acid-fast organisms in a clinical specimen always suggest?
Not always. Saprophytic Mycobacteria are acid-fast positive and don't cause disease. The kinds of acid-fast organisms that do cause disease, like Mycobacterium tuberculosis, are more difficult to treat with antibiotics because of the large amounts of lipi
How should the acid-fast stain of a sputum specimen from a patient with suspected pulmonary Nocardia infection be performed?
The Acid-fast stain method, to detect the bacteria Nocardia starts by obtaining a sample of sputum, fluid from the trachea or lungs,or a sample of tissue collected during surgery. Preparing a smear for staining involves applying a very small sample to the
mixed culture
container growing two or more indentified species