Final Exam Lab Review

Question 1

what media is acidic and is great for the isolation of dermatophytes, fungi, and yeasts?

Answer 1

Sabouraud Dextrose Agar

Question 2

what media is reliable for isolating Staph aureus from foods?

Answer 2

Baird-Park Agar

Question 3

Who was Hans Christian Gram

Answer 3

inventor of the Gram stain, and the reason Gram is capitalized

Question 4

what media is able to differentiate between homofermentative and heterofermentative LAB?

Answer 4

HHD

Question 5

what is the OGYE agar used for?

Answer 5

selection and enumeration of yeasts and molds

Question 6

when would you use PALCAM agar?

Answer 6

the isolation of L. monocytogenes from food items

Question 7

which media supports good growth of lactobacilli in general?

Answer 7

MRS

Question 8

What is the Muller Hinton Agar used for?

Answer 8

antibiotic susceptibility testing

Question 9

what are some reasons that Muller Hinton Agar is great for antibiotic susceptibility testing?

Answer 9

• nonselective
• non-differential
• absorbs toxins released from bacteria
• loose so you get diffusion of antibiotic throughout the agar

Question 10

what are the steps of the gram stain?

Answer 10

fixate. then:
1) flood slide with crystal violet for a minute then rinse
2) flood slide with iodine for a minute then rinse
3) flood the slide with decolorizer (ethanol) for a 30 seconds then rinse
4) flood with safranin for a minute then rinse

Question 11

what species are involved with yogurt production?

Answer 11

Streptococcus thermophilus & Lactobacillus Bulgaricus

Question 12

Which species has a bi-phasic growth curve in yogurt production?

Answer 12

S. thermophilus

Question 13

which species has a longer initial lag time in yogurt production? why?

Answer 13

L. bulgaricus. it isn’t until it receives growth factors (formic acid & CO2) from S. thermophilus that L. bulgaricus is stimulated to grow faster

Question 14

what was the idea of the maple syrup lab?

Answer 14

the syrups contained different amounts of water content, and the lab’s purpose was to observe the difference in their spoilage.

Question 15

if maple syrup 1 had more water content than 2, what does that mean about their sugar contents?

Answer 15

1 has less sugar, 2 has more

Question 16

which type of organism will be responsible for the spoilage of syrup 1 and 2?

Answer 16

syrup 1 (more water): bacteria
syrup 2 (less water): mold

Question 17

which syrup will have a rapid drop in pH?

Answer 17

the syrup spoiled by bacteria

Question 18

what was the idea of the antibiotic resistance lab?

Answer 18

• samples taken from meat are plated on TSA agar supplemented with the antimicrobials, tetracycline and ceftiofur. any surviving colonies show a degree of resistance to these antimicrobials
• the isolated colonies are further tested for resistance on MHA plates with 4 different antimicrobial disks on them (tetracycline, ampicillin, erythromycin, streptomycin)

Question 19

what is the usual CFU of microbes on raw meat products?

Answer 19

10^2 to 10^5 CFU/cm^2 of aerobic mesophiles

Question 20

if you plate the homogenized meat samples onto plates containing tetracycline and ceftiofure, why are you only plating 10^-1 and 10^-3

Answer 20

the actual amount of bacteria that can grow in these conditions would be very small so we need these higher concentrations

Question 21

why do we include ceftiofur on this plate?

Answer 21

it has veterinary applications in commercial agriculture, which is applicable to the purchased meats in the lab.

Question 22

are all isolates resistant to tetracycline?

Answer 22

If you isolate something on a plate containing tetracycline and then test using a tetracycline disc, you might not always see resistance. They are all resistant to tetracycline at some degree if you isolated them on a plate containing it, but there’s a higher concentration used on the disc

Question 23

what is the purpose of the easy fermenting lid in sauerkraut production?

Answer 23

• prevent entrance of O2 to maintain anaerobic conditions

- enable exit of CO2 so the container doesn’t explode

Question 24

what’s the purpose of adding salt in the initial sauerkraut culture

Answer 24

1) Selects for growth of LAB which are more resistant to more saline conditions
2) draw out juice from leaves to make sugars and nutrients readily available to LAB

Question 25

how many campden crush tablets do you add to your apple/water mix? why?

Answer 25

ONE

• kill wild yeast
• dechlorinate
• act as antioxidant

Question 26

what should your airlock look like about 24 hours after adding yeast?

Answer 26

some bubbles, popped off top

Question 27

if you are not seeing CO2 discharge during your wine ferment, what could be the problem? what may be the result?

Answer 27

you likely have a stuck ferment. the result can smell like sulfur and you won’t get an ideal alcohol content