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micro lab test 1


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how does a negative stain differ from other stains?
The dye is acidic and has a negative charge
What is a benefit of using a negative stain?
You don't have to heat fix (good for fragile organisms/cells). Also, it produces minimal cell shrinkage.
What is the theory behind using an acidic stain?
The negative charge repels the stain, so the cell remains uncolored against a colored background.
What are two common acidic stains
nigrosin and eosin
What is an autoclave bag?
It is used for decontamination. The items from the bag are put into an autoclave to sterilze them at 121 degrees
needles and glass should be put in
sharps container
bright field microscopy is the
most commonly used
the best limit of resolution is
.2 micrometers
total magnification is
mag of objective x mag of ocular
eyeball to base of microscope
ocular lens, objective lens, specimin, condensor, light
Actual limit of resolution
wavelength /
NA condensor + NA objective
Numeric Aperture is the
measure of a len's ability to capture light coming from the specimin and use it to make an image
stage micrometer
used to calibrate microscope
(no numbers on it)
ocular micrometer
is a scale with uniform incrmenets of unknown size. It has to be callibrated with the objective
two cocci
chain cocci
four cocci
eight cocci
grape like structure
short rod that could be confused with cocci
curved rod
grows in a variety of shapes
basic steps in making a bacterial smear
drop water, add bacteria w innoc. loop, spread, air dry (flame loop again), pass through flame
2 benefits of making bacterial heat fixed smear?
it makes the bacteria adhere to the slide and it coagulates the protein to make them more visible
drawbacks to heat fixing a smear?
it distorts the cells to an extent.
theory behind basic stain
basic stains are attracted to the negative charge on the surface of most bacterial cells. Thuis the cell becomes colored
3 common basic stains
methylene blue, safranin, crystal violet
how is negative stain different from other stains?
The dye is acidic and has a negative charge
examples of differential stains?
gram, acid fast, capsule, spores or flagella
differential stains are also referred to as
structural stains
what is the Ziehl-Neelsen (ZN) method and sequence of steps
Acid fast stain.
heat fix emulsion, cover smear w paper towel and carbolfucshin stain, steam for 5 min, remove paper, rinse, decolorize w acid alcohol, rinse w distilled water, counterstian w M. blue 1 min., blot dry
function of the methylene blue in acid fast?
It stains the acid fast negative cells
2 diseases caused by mycobacteria?
leprosy and tuberculosis
function of capsule stain
detects cells capable of producing an extracellular capsule.
capsule production
increases virulence in some microbes, making them less vulnerable to phagocytosis
capsule technique
stains around cells. The capsule remains unstained and appears as a white halo against a colored background.
capsules are composed of
polypeptides which are difficult to stain
what is an endospore
a dormant form of bacterium thatb allows it to survive lean environmental conditions
Endospore stain process
heat fixed smear, cover w paper. apply malachite green steam 5 minutes, counterstain w safranin 1 min, rinse, blot dry
endoposre stain chemicals
malachite green and safranin
2 genera of bacteria w endospores
bacillus and clostridium
would bacteria be likely pathogenic at 25 degrees?
Probably not psychrotrophs, usually are not pathogenic
would bacteria be likely pathogenic at 37 degrees?
free living
microbe does not reside on plant or animal host and are not pathogenic.
opportunistic pathogen
capable to cause disease
area including sites outside the host where microbe resides and serves as a poential source of infection
associated w host
circular, irregular, punctiform (tiny, pinpoint)
entire (smooth, no irregularites), undulate (wavy), lobate (lobed), filamentous, or rhizoid (branched like roots)
flat, raised, convex, pulvinate (very convex), and umbonate (raised in center)
mucoid, moist or dry
pigment description
color, opaque, translucent, shiny or dull

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