Lecture 1-3

Question 1

Agar

Answer 1

-complex polysaccharide from marine red algae
-used in petri dishes

Question 2

Chemically defined media

Answer 2

Exact chemical composition is known

Question 3

Complex media

Answer 3

Extracts and digests of yeast, meat, or plants
-composition not known

Question 4

Streak plate method

Answer 4

used to isolate pure colonies

Question 5

What is TSA plate

Answer 5

Tryptic Soy Agar
-isolate microbes from surfaces
-not differential

Question 6

What is differential media

Answer 6

-differentiate microbes based on ability to metabolize specific nutrients
-produce visible colors
-can sometimes be selective

Question 7

What is selective media

Answer 7

Suppress unwanted microbes and encourage desired ones

Question 8

What kind of media is MacConkey agar and how does it work

Answer 8

Selective and differential
-Gram (-) bacteria grow, (+) does not grow–>differential (contains bile salts and crystal violet)
-Differentiates between lactose fermenters and non fermenters–>turns red if lactose (+), turns yellow if lactose (-)

Question 9

What kind of medium is Kings B medium, what is used for and how does it work)

Answer 9

-Enriched differential medium
-anything can grow but differentiates if pseudomonas fluorescens grows b/c it turns blue-green due to pyoverdine
-Has magnesium sulphate

Question 10

True or false: King’s B is a selective medium?

Answer 10

False
-It is a differential medium that will turn blue-green if it is P.fluorescens
-anything can grow on it

Question 11

What is pyoverdine?

Answer 11

A type of siderphore that Pseudomonas uses to scavenge iron from environment

Question 12

What is a siderophore?

Answer 12

Used to sequester iron (Fe3+)

Question 13

Why does bacteria need iron

Answer 13

Iron is used in the electron transport chain

Question 14

What are biofilms and why are they important?

Answer 14

Microorganism form communities as a way for microbes to survive–>stay stuck to a surface while environment changes
-share nutrients
-shelter from harmful factors
-from slime/hydrogels

Question 15

How does biofilm help with resistance?

Answer 15

The biofilms protect the cells, and the cells may not be actively dividing
-antibiotics only work when cells are actively dividing
-exopolysaccharide protects bacteria and antibiotics cannot enter

Question 16

What are some biofilms in eukaryotes?

Answer 16

-Candidia albicans cause vaginitis, diaper rash, oral thrush
-S. cerevisiae form biofilms on plastic surfaces and soft agar

Question 17

True or false: P. fluorescens in a shaking environment always forms a biofilm

Answer 17

False
-P. fluorescens in shaking environment will NEVER form a biofilm
-The shaking does not disrupt the biofilm, the reason why it does not form is b/c in shaking oxygen is distributed throughout the tube
-in static oxygen will only be at the top forcing the bacteria to form a biofilm to survive

Question 18

Where do you expect to see the biofilm for P. fluorescens in static conditions?

Answer 18

Interface between air & medium (top)
-b/c P.fluorescens is strictly aerobe and it needs oxygen so it will go to the top

Question 19

What dictates the metabolic pathway for bacteria?

Answer 19

Oxygen

Question 20

Obligate aerobes

Answer 20

Needs oxygen
-cells found at top of tube
-Ex: P.fluorescens

Question 21

Obligate anaerobes

Answer 21

-Hates oxygen
-found at the bottom of tube
-Ex: Clostridium botulinum

Question 22

Facultative anaerobe

Answer 22

Prefers. oxygen, but can live without
-Mostly at top of tube with cells throughout the rest
-Ex: Salmonella, E.coli, S. cerevisae

Question 23

Microaerophiles

Answer 23

-Uses 2-10% oxygen (little amount)
-Found near the top, with a little underneath
-Ex: Helyobacter pylori

Question 24

Aerotolerant anaerobes

Answer 24

Ignores oxygen, do not use oxygen only live in the presence of oxygen
-Found at top (oxic zone)
-Found in rest tube (anoxic zone)
-Ex: Lactobacillus acidophilus

Question 25

What kind of oxygen does P.fluorescens need

Answer 25

-Obligate aerobe
-NEEDS oxygen

Question 26

Why do we use Kings B medium for P. fluorescens

Answer 26

-Does not contain thioglycolate or agar, most bacteria would sink
-Biofilm allows them to float and use oxygen effectively

Question 27

What do wrinkly cells from biofilm mean

Answer 27

Have mutations from biofilm formation

Question 28

What is the standard plate count

Answer 28

A serial dilution and spread plate
-used to estimate the number of cells from the original sample

Question 29

How to calculate the dilution factor?

Answer 29

FINAL VOLUME/INITIAL VOLUME

Question 30

True or false: the dilution factor is always less than 1

Answer 30

False
-Dilution factor is always more than 1

Question 31

True or false: DF is the reciprocal of dilution

Answer 31

True

Question 32

True or false: The dilution is always less than 1

Answer 32

True

Question 33

How to calculate culture density (CFU/ml)

Answer 33

number of colonies/(dilution factor) x (volume plated in mL)

Question 34

How many colonies need to be on a plate to be countable?

Answer 34

30-300

Question 35

What is the difference between a serial dilution and a dilution series?

Answer 35

-A serial dilution has the same dilution factor for ALL tubes
-A dilution series has at least 1 tube that has a DIFFERENT dilution factor

Question 36

What is quorum sensing?

Answer 36

How microbes communicate
-needs enough bacteria to produce a signal/communicate

Question 37

What are biofilms associated with?

Answer 37

-Catheters
-Pacemakers
-Aortic valves