bacteria cultivation

Question 1

what are the 4 phases of bacterial growth and what happens in each l

Answer 1

lag - metabolism to acquire essential nutrients ready to divide
exponential - binary fission
stationary- essential nutrients depleted and toxic metabolic products accumulate
decline - old cells die rapidly followed by young cells

Question 2

ways to count bacteria

Answer 2

microscopic counting
colony counting
opacity/turbidity

Question 3

bacterial nutrition requirements

Answer 3

raw materials essential for growth
large quantities of C and N
peptones = meat, protein, amino acids
phosphates - nucleic acid production
sulphur= amino acid production
Ca, Fe, Mg, K= important enzyme co-factors

Question 4

temperature range of mesophilic bacteria

Answer 4

20 - 45

Question 5

temperature psycrophiles prefer

Answer 5

15

Question 6

temperature thermofiles prefer

Answer 6

60

Question 7

oxygen requirements of aerobes

Answer 7

obligate

Question 8

oxygen requirements of microaerophiles

Answer 8

small amounts

Question 9

oxygen requirements of anaerobes

Answer 9

do not require

Question 10

obligate anaerobes

Answer 10

killed/inhibited by oxygen

Question 11

aerotolerant anaerobes

Answer 11

killed by oxygen

Question 12

facultive anaerobes

Answer 12

can grow with/without oxygen

Question 13

why are micro-organisms preserved

Answer 13

vaccine production
research and teaching

Question 14

how are micro-organisms preserved

Answer 14

freezing in liquid nitrogen at -190
dessication - freeze drying then stored as ampoules in dark

Question 15

methods to prevent food spoilage/limit pathogens

Answer 15

refrigeration at 4 degrees = prevents microbe multiplication as slows enzymatic reactions (listeria still grows)
freezing at -20 (survivors multiplied rapidly if thawed)
boiling at 100 - inactivation of bacteria/fungi (endospores may still survive)
vacuum packing - oxygen removal prevents aerobe growth
pasteurization - flash and ultra high temperatures

Question 16

physical methods of inactivation

Answer 16

heat - denature enzymes and proteins
thermal death point - lowest temp at which all microbes in liquid suspension killed in 10 mins
thermal death time - minimal length of time all bacteria killed at a given temp
decimal reduction time - time for 90% of bacteria at given time

Question 17

method of moist heat sterilization

Answer 17

autoclave

Question 18

dry heat sterilisation methods

Answer 18

direct flaming eg bunsen burner
incineration
hot air

Question 19

filtration sterilization methods

Answer 19

air filtration
membrane filters

Question 20

radiation sterilization methods

Answer 20

gamma
UV light

Question 21

actions of microbial control agents

Answer 21

alteration of membrane permeability
damage to proteins
damage to nucleic acids

Question 22

chemical methods for inactivation

Answer 22

osmotic pressure
acidification
sulfur dioxide
disinfectants