MICROSCOPY
What magnification on a microscope should the oil immersion technique be used on?
100x
What is the difference between a differential stain and a simple stain?
Differential has 2+ dyes, Simple has 1
The streak plate technique is the single most important dilution method to accomplish __________.
The isolation of pure cultures
what is the difference between staphylococcus and streptococcus bacterial arrangements?
Streptococcus forms a linear plane, staphylococcus forms a cluster
What is the purpose of an indicator in agar?
Indicators change color based on pH or other specific metabolic products. These indicators make it very easy to identify different metabolic biochemistries by the naked eye.
What is the purpose of the condenser?
To collect and direct light toward the slide
Why would we use a basic dye vs an acidic dye?
The dyes used in the simple staining process are basic dyes that contain positively charged chromophores (colored ions), which will be attracted to the negatively charged components on the cell’s membrane and wall. An acidic dye contains negatively charged ions that repel the bacterial cell and do not stain effectively.
How do you properly label a petri plate?
Use the Sharpie™ marker and label the bottom of the TSA plate with at least your initials & date, organism name(s), and the name of the medium. For easier viewing of microbial growth, label around the perimeter of the plate surface.
How does the Bunsen burner act as a type of aseptic technique?
The flame creates a sterile field, as microbes and particles are forced upwards around the heat/flame.
MacConkey's agar will only grow bacteria that are __________.
Gram-Negative
How do you find the total magnification a compound microscope?
The total magnification of a compound microscope is determined by multiplying the magnifying power of the ocular lens by that of the objective lens used.
Why should young cultures (18 to 24 h) be used for staining?
Cultures that are older than 24 h may not take up the crystal violet/iodine complexes due to the deterioration of the peptidoglycan layer; these old cultures inappropriately appear gram negative.
What is the difference between the spread plate technique and the streak plate technique?
Utensil, goal (growth vs isolation)
What are the two purposes of heat fixation?
Killing the bacteria, and adhering it to the slide
Mannitol Salt agar (MSA) is commonly used to differentiate among bacteria in the __________.
Staphylococcus genus
List 3 reasons why you may be unable to find any bacteria while looking through a microscope
Light isn't on/is not plugged in, microscope is not focused, lens is dirty/eroded, improper technique for staining, the stage keeps moving with focusing
Why is time an important factor in simple staining?
Time is important because it creates a contrast between the bacteria and the stain. If you over or under stain you won't be able to see bacteria.
How does smear preparation of cells from a liquid medium differ from the preparation of cells from an agar surface?
Give an example of bacterial colony: form, elevation, and margin (1 for each)
Form: punctiform, circular, filamentous, irregular, rhizoid, spindle
Elevation: Flat, raised, convex, pulvinate, umbonate
Margin: Entire, undulate. lobate, erase, filamentous, curled
If EMB agar shows bacterial growth in a green, metallic color what can you know about the bacteria growing?
Gram-negative fermenter
In microbiology, what is the most commonly used objective? Explain your answer.
Being able to view microscopic organisms.
List the steps for gram staining. Include regents and their purpose, timing and order.
Answer is too long for text box to hold.
Killed bacteria with too hot of a loop, sample was too diluted, not long enough incubation time....
Define Bacteriostatic
Prevents the growth of bacteria (i.e., it keeps them in the stationary phase of growth)
is HE agar selective, differential or both? List all of the applicable selective, differential and or indicator components
The selective: bile salts
The differentiation: actose, sucrose, and salicin
The indicators: Ferric ammonium citrate and sodium thiosulfate