Microbiology Midterm

study this one and quiz one flashcards

<1mm colony size is considered…

pinpoint

1-2mm colony size is considered

small

2-3mm colony size is considered

medium

>3mm colony size is considered

large

transparent colony means it is

clear

translucent colony means it is

nearly clear

a frosted appearance to a colony is considered

opaque

an iridescent colony means

it changes color as the plate is tilted

what is an example of a bacteria whose colonies are iridescent

pseudomonas aeruginosa

what does it mean for a colony to be butyrous

buttery consistency

what does it mean for a colony to be friable

it is brittle and falls apart

what does it mean for a colony to be viscous

it sticks to the loop

what does it mean for a colony to be mucoid

it is slimy and strings from the loop

what is beta hemolysis

clear halo around the colony

what is alpha hemolysis

green halo around the colony

what is gamma hemolysis

no hemolysis

what color is MAC lactose fermenter

pink

what color is MAC non lactose fermenter

yellow or no color

what bacteria is known for smelling like grapes

pseudomonas aeruginosa

what bacteria is known for smelling like bleach

Eikenella corrodens

what is a direct gram stain

stained bacteria taken directly from the colony

what is an indirect gram stain

stained bacteria that comes from a plate after growth

what kind of media should you not take bacteria from for an indirect gram stain

selective

fixing a slide ensures

• all vegetative organisms are killed

• preservation of the bacteria from changes

• improved adhesion to the slide

• improved penetration of the stain into the cell wall

what is the best way to fix a slide

flooding the slide for 1 minute with 95% methanol

flooding the slide with 95% methanol is best for

• preserving cell morphology

• best for morphology of WBC, RBC and epithelial cells

• best for bloody specimens

what is a simple stain

one dye or stain is used so everything on the smear is stained the same

what is an example of a simple stain

methylene blue

what is a downside of using simple stain

we can only determine the cell shape

what is differential stain

separates bacteria into different groups depending on staining properties

examples of differential stains include

Gram stain , Acid Fast stain

what is acid fast stain used for

to demonstrate bacteria with mycolic acids in the cell wall

gram stains on acid fast bacteria are either…

gram positive, gram ghosts or gram neutral

What kind of stain in Ziehl-Neelsen

acid fast

what makes Ziehl-Neelsen stain different from Kinyoun

ZN requires heat where Kinyoun does not

what do positive acid fast bacteria look like after staining with Ziehl-Neelsen

red bacteria with a blue background

what is the counter stain for Ziehl-Neelsen

methylene blue or malachite green

how is kinyoun different from Ziehl-Neelsen

has a higher phenol concentration

what kind of stain is Kinyoun

acid fast

what kind of stain is Auramine rhodamine

acid fast

what kind of stain is Acridine orange

special

what does acridine orange stain for

binds non specifically with nucleic acids

what can acridine orange detect

mycoplasma

what kind of stain is auramine-rhodamine

special

what does auramine-rhodamine stain for

binds non specifically to mycobacteria

what kind of stain is Calcofluor white

special

what does calcofluor white stain for

direct detection of fungus

what kind of stain is immunofluorescence

special

what does immunofluorescence stain for

antibody/antigen attachment

what bacteria is immunofluorescence good for

chlamydia trachomatis

what does dark field microscopy detect

spirochetes such as treponema pallidum

what are wet mounts

where microbes are visualized in a living state to see motility

what are negative stains

the background of the smear is colored instead of the bacteria

what is used in negative stains

India ink

what is a bacteria that uses negative staining

cryptococcus neoformans in CSF

What can not be detected with a gram stain

intracellular pathogens

can not be detected by a gram stain

organisms without a cell wall

what can not be detected by a gram stain

organisms with insufficient dimensions to be resolved

what is an example of a bacteria that is an intracellular pathogen

chlamydia spp.

what is an example of a bacteria without a cell wall

mycoplasma spp.

what is an example of an organism with insufficient dimensions to be resolved

spirochetes

what is the primary stain in a gram stain

crystal violet

what is a trapping agent in a gram stain

bonds alkaline dye to the cell wall

what is an example of a trapping agent in a gram stain

Gram’s or Lugols iodine

what is an example of a decolorizer in a gram stain

acetone and/or alcohol

what is the most important step during the gram stain process

decolorizer

what is the secondary stain in the gram stain

safranin - neutral red

a direct gram stain can not be performed on

feces

you can not perform a direct gram stain on

throat swabs

direct gram stains can not be performed on

nasopharyngeal specimens

what causes the crystal violet stain to run out of gram negative organisms

higher lipid content in the cell wall making them more porous

what causes crystal violet to be trapped in gram positive organisms

thicker cell walls

over decolorization causes gram positive organisms to

lose crystal violet stain and appear red/pink

under decolorization causes gram negative organisms to

not have crystal violet removed resulting in a purple appearence

when observing cells under a direct gram stain, phagocytes are an indicator of

inflammation

when observing cells under a direct gram stain, epithelial cells are an indicator of

possible contamination

do you see host cells in an indirect gram stain

NO

what type of gram stain is recorded, but not reported to the doctor

indirect

gram positive organisms will appear pink if

• cell wall is damaged

• affected by antibiotics

• old age

• autolytic enzymes

• over decolorization