lecture 2

Question 1

Example of food spoilage fermentative bacteria?

Answer 1

lactic acid bacteria spoils in milk

acetic acid bacteria spoils wine to taste like vinegar

Question 2

Example of good fermentative bacteria

Answer 2

lactococcus baccilus lactic acid bacteria in cheese

acetic acid to make vinegar

Question 3

Example of bacteria that is not good for human skin but good for food

Answer 3

propionibacteria causes acne but propionibacterium freundenreichii (of same family) used for swiss cheese

Question 4

What does propioni freund. produce that gives swiss cheese its characteristics

Answer 4

lactic acid -> propionate + acetate + CO2

Question 5

What are the 4 growth phases ? describe them, draw the growth curve

Answer 5

lag = adaptation to media/env
log = exponential growth
stationary = slow growth due to high population, reached carrying capacity: not enough substrates
Death = crash

Question 6

where on the graph is log phase

Answer 6

curve after lag, not steady slope before stationary

Question 7

5 common places to find microbes

Answer 7

animals, birds (esp pathogens)
air (those that survive dry env : fungi, spore)
soil
insects
raw ingredients - soft rot bacterua (pseud. erwinia, pectobacterium, xanthomonas)
- yeast where there’s suguar
- lactic acid bacteria

Question 8

description of growth in equation

Answer 8

N = N(o) e^(e mu)

Question 9

doubling time

Answer 9

0.693/mu

Question 10

microbe temperature preference from cold to hot

Answer 10

psychrophile - psychrotroph - mesophile - thermophile

Question 11

Why are most organisms neutrophile/acidophile? not alkaliphile?

Answer 11

food sources are neutral/acidic

Question 12

3 microbe preference for solutes

Answer 12

Halophiles (require at least 0.3M salt)
Halotolerant can grow in salt, not optimal
Xerotolerant grow on very dry foods
Osmotolerant survive in high osmorality

Question 13

Describing microbes based on energy source?

Answer 13

organotrophs: energy through organic cells
phototroph photosynthesis
litotroph through oxi/red of metals

Question 14

How is the outer membrane of bacteria different from its inner membrane?

Answer 14

outer membrane permeable to ions, smalal molecules

inner membrane permeable only to small hydrophobic or uncharged molecules (more specific, less permeable)

Question 15

G-ve different from G+ve because

Answer 15

lipopolysaccharide outer membrane