Exam 2 - Lecture 8

Question 1

what are some things microbes can do to endure periods without nutrients?

Answer 1

• form endospores
• enter a dormant, metabolically inactive state
• synthesize starvation response proteins
• make biofilms

Question 2

when microbes grow in free floating in liquid, it is called ___________ growth.

Answer 2

planktonic growth

Question 3

when microbes grow attached to surfaces in communities, it is called a:

Answer 3

biofilm

Question 4

what holds the bacteria together in a biofilm?

Answer 4

extracellular polymeric substances (EPS)

Question 5

what kinds of molecules can be found in a biofilm matrix?

Answer 5

• polysaccharides
• proteins
• DNA

Question 6

true or false: biofilms are not uniform.

Answer 6

true

Question 7

is it more likely for there to be more than one species in a biofilm or just one?

Answer 7

more than one

Question 8

what causes differences in the metabolic activity of microbes in a biofilm?

Answer 8

heterogenous exposition of bacteria to different environmental conditions in different parts of the biofilm

Question 9

true of false: biofilm bacteria are fairly easy to kill.

Answer 9

false; they are extremely difficult to kill.

Question 10

what makes biofilm bacteria hard to kill?

Answer 10

• the matrix protects them from harmful agents (UV, antibiotics, antimicrobials)
• altered physiologies make them less sensitive

Question 11

how do bacteria communicate in/out of the biofilm?

Answer 11

in a density-dependent manner called quorum sensing

Question 12

as they grow, what do bacteria in a biofilm start producing?

Answer 12

autoinducers that diffuses out of the cell that alters gene expression when it diffuses back inside because it did some quorum sensing

Question 13

what are the two major types of autoinducer cells?

Answer 13

• N-acyl-homoserine lactones (AHLs, Gram-negative)
• autoinducer peptides (AIPs, Gram-positive)

Question 14

culture media can be prepared as ________ or _________

Answer 14

solid or liquid

Question 15

how is media classified?

Answer 15

• chemical constituents from which they are made
• physical nature
• function

Question 16

what are the two major types of media?

Answer 16

• chemically defined (or synthetic)
• complex

Question 17

what are some media components?

Answer 17

• peptones: protein hydrolysates (fragments) prepared by partial partial digestion of various protein sources
• extracts: aqueous extracts, usually beef or yeast
• agar: polysaccharide (extracted from algae) use to solidify liquid media. most microorganisms can’t degrade it

Question 18

what are four types of functional media?

Answer 18

• supportive (general use) media that supports the growth of many microorganisms, example: TSA
• enriched media that is supplemented by blood or other special nutrients, examples: blood agar, chocolate agar
• selective media: favors the growth of some microbes and inhibits the growth of others
• differential media: distinguishes between groups of microbes based on their biological characteristics

Question 19

what does MacConket agar select for?

Answer 19

Gram-negative bacteria

Question 20

what is the purpose of plate streaking?

Answer 20

to isolate single colonies

Question 21

a population of cells arising from a single cell is called a:

Answer 21

colony

Question 22

what is the statistically significant range for number of colonies on a plate?

Answer 22

30-300

Question 23

what are the characteristics, such as size and shape, of a colony called?

Answer 23

the colonial morphology

Question 24

what are the four phases a bacterial growth curve?

Answer 24

• lag phase
• exponential phase
• stationary phase
• death phase

Question 25

what is taking place in the lag phase?

Answer 25

• cells are adapting to their new environment/media
• cells are synthesizing new components
• lag phase isn’t always the same length

Question 26

what characterizes the exponential phase?

Answer 26

• aka the log phase
• rate of growth an division during this time is constant
• high metabolism and nutrient availability
• population is most uniform in terms of chemical and physical properties during this phase

Question 27

what characterizes the stationary phase?

Answer 27

• nutrients are depleted
• metabolic byproducts build up
• population growth slows and eventually stops
• reproduction stops
• number of viable/living cells stays constant

Question 28

what does entry into the stationary phase activate in the bacteria?

Answer 28

survival strategies (morphological changes like endospore formation, dismantling of ribosomes, decrease in size, nucleoid condensation, protoplast shrinkage, yeah)

Question 29

when you do and spread and pour plate technique for counting colonies, are the CFUs that you are counting alive?

Answer 29

yes, this method only counts living cells. then you multiply by the dilution factor

Question 30

what is the disadvantage of counting chambers?

Answer 30

you can’t distinguish between living and dead cells

Question 31

what is turbidity?

Answer 31

the cloudiness or haziness of a fluid caused by suspended particles

Question 32

what is a turbidometric measurement?

Answer 32

a measurement of turbidity or scattering of light

Question 33

what wavelength is used in optical density measurements?

Answer 33

600 nm

Question 34

a high absorbance means there is a (high or low) number of cells being detected.

Answer 34

high