Quiz 1 Flashcards
Aseptic Technique Gram Stain Negative Stain
3 Reasons aseptic technique is used
- no contaminating organisms introduced to culture 2. organisms do not contaminate the handler 3. no contamination remains after work is over
How heat is used (2 examples)
- after cap is removed from organism tube 2. loop
Where should a label be written on an agar plate?
Bottom of plate
How should agar plates be incubated?
upside down to prevent condensation on agar surface
Which organisms are effective against disinfectants?
vegatative cells not endospores
What disinfectants used in the lab
staphene
What type of chromopore is associated with a negative stain?
negatively charged chromopore
example of negative stain
nigrosin
what step is omitted when the dimension of cells are determined?
heat fixation because it shrinks the cells
what external bacterial cell structures can be demonstrated by a negative stain?
flagella
Why is a gram stain a differential stain?
it takes advantage of the fact that different types of cells react differently to stains
how to gram positive and gram negative bacteria differ in cellular structure
gram positive- thick layer peptidoglycan
gram negative- 2 membranes and thin peptidoglycan layer
how does the age of a culture affect the gram stain reaction? what is an optimum culture age for a valid gram reaction?
If a gram positive is older than 18 hours, it can covert to gram variable or gram negatve.
optimum time is 16-18 hours
Which step in gram stain is prone to error?
decolorizer- if too much is added gram + will turn pink and if too little is added gram - stays purple
what is the function of mordant - which reagent is used
mordant forms a complex with the primary stain
grams iodine is used- complex with crystal violet
list reagents of gram stain technique
- crystal violet (primary) 2. grams iodine (mordant) 3. alcohol (decolorizer) 4. safranin (counterstain)
in what type of cell would you find lipopolysaccharide in its cell wal
gram negative
