microbial growth lecture 2

Question 1

why is agar a better substitute than gelatin 2

Answer 1

1. agar is not destroyed by microbes

2. higher MP melts only at 100 degrees celcius

Question 2

who produced evidence that bacteria could cause disease?

what bacteria did he inject into healthy mice

Answer 2

Robert Koch

-Bacillus anthracis

Question 3

def of Koch’s postulates

Answer 3

criteria from providing the relationship between a microorganism and a specific disease

Question 4

Koch’s postulates consists of 4 stages

Answer 4

1. respective microorganism must be present in every sick individual but absent from healthy individuals
2. isolate the suspected microorganism and grow into a pure culture
3. inoculate healthy host with the isolated microorganism - same disease should occur
4. re-isolate microorganism from diseased host

Question 5

5 factors that influence microbial growth

Answer 5

1. nutrients
2. temperature
3. pH
4. oxygen requirements
5. osmotic pressure

Question 6

macronutrients

Answer 6

required in high amounts for cell components and metabolism e.g. carbon, oxygen and phosphate

Question 7

micronutrients

and another name

Answer 7

trace elements

-required in lower amount for enzyme function and to maintain protein structure

Question 8

heterotrophs

Answer 8

must obtain their carbon in an organic form e.g carbohydrates and proteins

Question 9

autotrophs

Answer 9

• use inorganic carbon, CO2 and convert it into organic compounds
• form the base of food chains that support all other life forms

Question 10

in the presence of oxygen respiration occurs what are the products

Answer 10

CO2 , NADH and FADH2

Question 11

in the absence of oxygen fermentation takes place, what are the products

Answer 11

CO2 and ethanol

Question 12

obligate anaerobes

Answer 12

• oxygen=toxic
• cannot grow in oxygen’s presence
• cultured in N2 or CO2

Question 13

obligate aerobe

Answer 13

-dependent on O2

Question 14

facultative anaerobes

Answer 14

• do not require oxygen

- but grow better in its presence

Question 15

aerotolerant

Answer 15

not influenced by presence/absence of oxygen

Question 16

microaerophiles

Answer 16

require 2%-10% O2

Question 17

are fungi aerobic/anaerobic?

Answer 17

aerobic

Question 18

are yeast aerobic/anaerobic? and specifically what kind

Answer 18

facultative anaerobes

Question 19

water activity Aw

Answer 19

amount of water available to a cell for growth

Question 20

pure water has the Aw of …

Answer 20

1

Question 21

hypotonic solution

Answer 21

• low solute concentration and therefore high water potential
• water moves into cell and cell swells and may even burst =lyse

Question 22

hypertonic solution

Answer 22

• soln has a high solute conc and low water potential

- water moves out of cell, cell shrinks and plasmolysis may occur

Question 23

plasmolysis

Answer 23

plasma membrane pulls away from cell wall

Question 24

osmotolerant

Answer 24

organisms that grow over a wide range of Aw

Question 25

which grows at a lower Aw bacteria or fungi

Answer 25

fungi grow at a lower Aw than bacteria and cause spoilage of dry foods such as bread

Question 26

osmophiles and an example

Answer 26

- grow only under high osmotic pressures | - e.g. halophiles which prefer high NaCl conc

Question 27

how are halophiles adapted to a high NaCl conc (3)

Answer 27

1-plasma membranes and cell walls= stabilized by high Na+ ion con 2-accumulate K+ ions in their cytoplasm to balance ionic strength outside of the cell 3-cell walls lack peptidoglycan to allow for more cell wall flexibility

Question 28

growth media can be divided into to main groups

Answer 28

1. chemically defined (synthetic) media | 2. complex media

Question 29

chemically defined (synthetic) media

Answer 29

composed of known ingredients at known concentrations

Question 30

complex media

Answer 30

- rich in vitamins and other nutrients, of which precise chemical composition of media is undefined - can vary depending on the supplier

Question 31

media can be prepared in 3 forms

Answer 31

1. liquid 2. semi-solid 3. solid

Question 32

what is liquid media used for

Answer 32

fermentation, to measure biomass

Question 33

microbial growth in liquid media can be detected in 4 ways

Answer 33

1. turbidity of liquid media 2. pellicle formation where a mass of cells float on the surface of the liquid media 3. sediment formation where cells deposit on the bottom of the tube 4. slime production that binds cells together

Question 34

solid media is used for

Answer 34

examination of colony properties, isolation and storage of pure cultures

Question 35

semi-solid media used for

Answer 35

testing motility and oxygen requirements of organisms

Question 36

microbial growth

Answer 36

- increase in cell numbers and not size | - its exponential

Question 37

cell numbers can be expressed using 2

Answer 37

1-CFU in solid media 'colony forming units' 2-turbidity in liquid media (less accurate)

Question 38

4 stages of microbial growth in batch systems

Answer 38

1. lag 2. log/exponential 3. stationary 4. death

Question 39

batch system

Answer 39

- closed system with limited nutrients | - follows a growth curve

Question 40

3 characteristics of lag phase

Answer 40

1. no/very little cell division 2. cells may be under stress due to a change in environment 3. essential enzymes, cofactors and ATP have to be produced before growth can commerce

Question 41

exponential phase

Answer 41

microbes grow and divide at maximal rates

Question 42

stationary phase

Answer 42

1. growth plateau -level out

Question 43

4 reasons for stationary phase

Answer 43

Due to: 1-depletion of nutrients 2-lack of oxygen (aerobes) 3-decrease in pH as a result of organic acids produced during growth 4-accumulation of toxic byproducts

Question 44

death phase due to 2 things

Answer 44

1. nutrient depletion | 2. build up of toxic waste

Question 45

death phase

Answer 45

decline in number of viable cells

Question 46

4 ways to control microbial growth

Answer 46

1. temperature 2. irradiation 3. desiccation 4. filtration

Question 47

4 types of heat treatments to sterilize stuff

Answer 47

1. complete sterilization, temp in excess of 121 degrees celsius followed by autoclaving 2. pasteurization 3. tyndallisation 4. extremely low temp to slow/prevent microbial growth = bacteristatic (cannot permanentally sterilize)

Question 48

autoclaving uses a combination of | -it destroys bacterial spores

Answer 48

steam and pressure

Question 49

pasteurization

Answer 49

- only reduces the number and/or types of microbes | - relatively short term solution, the remaining microbes will start growing again

Question 50

3 types of pasteurization techniques include

Answer 50

1. LTLT-low temp, long time 2. HTST- high temp short time 3. UHT-ultra high temp

Question 51

tyndallisation

Answer 51

- breaks heat sensitive chemical bonds by flowing steam @ 100 degrees celsius for 30 min for 3 consecutive days - does not destroy dormant spores but any spores that germinate during that time are destroyed

Question 52

endospore vs spore

Answer 52

endospore=dormant, tough, non-reproductive structure

Question 53

irradiation 3 characteristics

Answer 53

- permanently damages the nuclei acids of organisms - bacterial endospores = resistant to irradiatio - can use 1. UV light-kills cells but low penetrating ability, best to sterilize surfaces 2. ionizing radiation (gamma and X-rays)- high penetrating ability, breaks sugar phosphate backbone of DNA

Question 54

desiccation

Answer 54

- inducing a hypertonic environment which inhibits microbes but dont completely eliminate them e. g. biltong

Question 55

filtration

Answer 55

temp-sensitive substances e.g. vitamins and antibiotics solutions have be sterilized by using a filter with a very small pore size that will retain most microbes