lab quiz 2 Flashcards
Match the following reagents with the purpose they serve in Gram stain:
Crystal violet primary stain
Iodine mordant
Alcohol decolorizer
Safranin counterstain
Which of the following statements is true regarding Gram+ bacteria? Check all that apply.
cell wall has a thick peptidoglycan layer
teichoic acids are present
lipopolysaccharide is absent
cell envelope lipid content is relatively low
Which step in the Gram stain is the most critical?
decolorization
In Gram staining, the alcohol acts on:
membrane lipid
What would most likely occur if you applied alcohol for only 1 second?
Gram-negative bacteria would not decolorize like it should, and all bacteria would therefore remain purple (Gram-positive)
+
What would most likely occur if you drenched the bacterial smear in alcohol for 1 minute?
All purple stain would escape as the cell wall of both Gram-positive and Gram-negative bacteria would dissolve
How long does it take to perform and analyze the Gram stain?
A few minutes
You have just performed Gram stain, and forgot to add the iodine. What colors would your Gram-positive (G+) and your Gram-negative (G-) bacteria look like?
G+ pink
G- pink
You have just performed Gram stain, and forgot to do the alcohol decolorization step. What colors would your Gram-positive (G+) and your Gram-negative (G-) bacteria look like?
G+ purple
G- purple
You have just performed Gram stain, and forgot to add safranin. What colors would your Gram-positive (G+) and your Gram-negative (G-) bacteria look like?
G- purple
G+ colorless
You have just performed Gram stain, and realized that you have reversed the order between crystal violet and safranin (safranin-iodine-alcohol-crystal violet). What colors would your Gram-positive (G+) and your Gram-negative (G-) bacteria look like?
G+ purple
G- purple
Match the following bacteria with their shape and arrangement.
Staphylococcus aureus Gram+ cocci
Bacillus subtilis Gram+ rod
Serratia marcescens Gram- rod
Chromobacterium violaceum Gram- rod
Match the following dyes with their purpose for this week’s staining:
Calbofuchsin primary stain for acid-fast
methylene blue counter stain for acid-fast
malachite green primary stain for endospore staining
Safranin counter stain for endospore staining
Arrange the steps of acid-fast smear preparation in the correct order.
1 smear S. aureus in a drop of water
2 air dry and heat fix
3 Chop M. smegmatis on top of S. aureus
4 heat fix and leave slide on warmer until ready to stain
The reason you need to use steam heating for acid-fast staining is because:
High mycolic acid (wax) content in the cell wall of Mycobacterium
++
Which of the following is the differentiating step in acid-fast stain?
Acid alcohol
Place the staining procedure (acid-fast or endospore stains) in the correct order.
1 place a piece of bulbous paper on top of smear
2 saturate bulbous paper with primary dye
3 heat stream for 8-10 min, do not let slide dry
4 remove paper rinse and/or decolorize
Which of the following diseases could be diagnosed with acid-fast stain? Mark ALL that apply.
Tuberculosis
Leprosy
Cryptosporidium infection
Which bacteria are we using for endospore stain? Check all that apply.
Clostridium sporogenes
Bacillus cereus
Match the components of endospores with the materials they are made of.
Core DNA, ribosomes, etc
Membrane phospholipids
Cortex peptidoglycan
Coat proteins
Which of the following makes endospores resistant to extreme environments? Check all that apply.
DNA binding proteins
Low (no) metabolic activity
Cortex + Outer coat
Dipicolinic acid + Ca2+
Why does the endospore stain exercise call for an older (48 hour or 5 day) culture of Bacillus?
A new cultured of microbes needs enough time to be subjected to enough stress before it trigger sporulation.
If you were given a mixed culture containing gram-positive and gram-negative bacteria, and you need to separate them, what type of media would you use?
Selective
Choose the bacteria that are on your unknown ID gram-positive list. Check all that apply.
C. xerosis
S. aureus
B. cereus
Choose the bacteria that are on your unknown ID gram-negative list. Check all that apply.
K. pneumoniae
E. coli
S. enterica
Phenylethyl alcohol agar (PEA) is a(n):
selective medium
Bacteria in the genus Staphylococcus can grow on MSA because:
they live in high salt condition on the human skin
Match the following bacteria with the expected growth pattern on MSA:
Staphylococcus aureus yellow growth and halo
Staphylococcus epidermidis Pink or red growth, no halo
E. coli poor growth or no growth
Match the following color of phenol red with the correct pH range:
Yellow pH < 6.8
Red pH = 7.4 to 8.4
Pink pH > 8.4
Match the following ingredients of MacConkey to their specific functions.
Inhibitors bile salts and crystal violet
pH indicator neutral red
differential substrate lactose
Nutrients pancreatic digests, peptic digest
Match the following bacteria with the expected growth pattern on MacConkey:
Staphylococcus aureus poor growth or no growth
E. coli (fermenter) pink to red growth
Providencia stuartii (nonfermenter) colorless growth
Match the following color of neutral red with the correct pH range:
pink or red pHH < 6.8
Colorless pH > 6.8
