mibo lab exam 1

Question 1

used to carry the microscope (with base)

Answer 1

arm

Question 2

used for carrying microscope (with arm)

Answer 2

base

Question 3

collects and concentrates light into a tight beam on the specimen

Answer 3

condenser

Question 4

produces light to be passed through the specimen and into the objectives

Answer 4

light source

Question 5

adjusts amount of light being emitted from the light source

Answer 5

light intensity knob

Question 6

controls distance between specimen and objective by raising/lowering the stage in large increments

Answer 6

coarse focus adjustment knob

Question 7

controls distance between specimen and objectives by raising/lowering the stage in small increments

Answer 7

fine focus adjustment knob

Question 8

magnifies the specimen image

Answer 8

objective lenses

Question 9

platform that holds the specimen

Answer 9

stage

Question 10

allows image to be viewed with magnification

Answer 10

ocular lenses

Question 11

move clamped specimen across the stage

Answer 11

translational control knobs

Question 12

how to properly clean up your bench space

Answer 12

• dispose of all materials contaminated with organisms properly
• return equipment to the proper storage area
• discard all old cultures and slides into the appropriate waste containers

Question 13

Does talking or leaving dishes exposed to the air for prolonged times affect the amount of culturable microbes on a TSAYE medium agar plate?

Answer 13

yes, the longer the plate is out, the more likely culturable microbes from airborne microbes in the lab show up on the agar plates

Question 14

What were the different handwashing techniques used? What do the results of this indicate about under which conditions are more or less effective at removing microbes?

Answer 14

rinsing under water, rubbing hands, different time intervals, water temp
longer hands are rubbed under running water, the more effective technique

Question 15

What are implications for improper handwashing for both a) you leaving the lab, and b) a healthcare setting?

Answer 15

a) you can spread pathogenic microbes that you worked with in the lab to your surround environment
b) in healthcare you can infect yourself with microbes from your patients, or spread microbes between patients which can have detrimental effects

Question 16

Describe the purpose of ‘aseptic’ technique

Answer 16

used to avoid contamination which cannot be visualized but can alter experimental results
reduces the risk of spreading microbes

Question 17

Describe the order of steps to perform a culture transfer following aseptic technique

Answer 17

hold sterilized loop in dominant hand
remove cap w/ little finger
pull cap off
pick of cells with sterilized loop
place cap then put down tube
transfer cells to tube containing medium

Question 18

Describe the steps we use to streak for isolation

Answer 18

• label plates as indicated
• use sterile loop to inoculate top of plate and spread it back/forth
• Spread modest amount of culture in small patch
• get a new stick and pass through previous patch and streak a small new area nearby
• get a new stick and pass through previous patch and streak a larger new area nearby
• get a new stick and pass through previous patch and streak a smaller/untouched area nearby

Question 19

What does the antibiotic cycloheximide do?

Answer 19

inhibits protein synthesis in eukaryotes and therefore inhibited the growth of fungi on plates where it is present

Question 20

What other additional features would you’d want to include when describing colony morphology?

Answer 20

color, size, texture

Question 21

What is the individual dilution factor (IDF), how do you calculate it?

Answer 21

describe the dilutions resulting from transferring a sample to a volume of diluent solution

• volume of sample/ volume or sample + diluent

Question 22

What is the total dilution factor (TDF), how do you calculate it?

Answer 22

how dilute a particular sample is relative to the original sample,

• product of all individual dilution factors (IDF x IDF x IDF… etc)

Question 23

Do you account for the volume used for plating when calculating the CFUs /mL in your original sample?

Question 24

How do you go from CFUs/mL of your original sample to total CFUs in your original sample?

Answer 24

CFU/mL = average colony forming units of plaque forming units on the plate/volume of the sample X TDF of the sample

Question 25

What are common cell morphologies and arrangements

Answer 25

• morphology: coccus
  arrangement: diplococci (2), tetrad (4), sarcina (8), streptococci (chains), staphylococci (clusters)
• morphology: bacillus
  arrangement: diplobacilli (2), streptobacilli (clusters)
• other morphologies: vibrio (bean), Spirillum (worm), spirochete (squiggle)

Question 26

Define in your own words what a ‘smear’ is

Answer 26

a sample that is thinly spread and fixed on a microscope slide

Question 27

In general terms, how does a differential stain allow us to distinguish microbes?

Answer 27

visualization of cells based on differences in their physiology in addition to their cell morphology

Question 28

Describe each step in the gram stain.

Answer 28

• sterilize your loop and dip in the first culture to collect cells
• transfer to the top of a microscope slide within a pre-drawn circle that corresponds to the culture you are using
• repeat process with the rest of the cultures
• allow the slide to dry completely on the slide drier
• heat-fix the cells to the slide by lowering over flame several times
• suspend the slide over the stain waste container
• apply crystal violet, wait 60 seconds, rinse
• apply lugol’s, wait 60 seconds, rinse
• add 2 drops of ethanol, rinse
• add safranin, wait 60 seconds, rinse
• blot dry with bibulous paper
• observe under oil immersion

Question 29

Name three errors that you could make when performing a gram stain. How would you design an experiment to identify if these errors were made?

Answer 29

too much ethyl alcohol was used on the sample causing a false negative
cells were not heat-fixed so they were easily rinsed off the slide
cells need to be <24 hrs or false negatives

Question 30

Yeast and mold are both fungi. How do they differ, how are they similar?

Answer 30

yeast
- unicellular, grow in colonies
- reproduce by budding
- produce catalase
mold
- grow in long, multicellular filaments known as
hypha
- one mycelium is made up of many hypha
- specialized hyphae form fruiting bodies which aid in reproduction forming spores

Question 31

Describe what the enzyme catalase does, and why it is important to cells?

Answer 31

prevents oxidative damage by breaking down hydrogen peroxide into water and oxygen