Lecture 4- Microbial growth

Question 1

What is bacterial growth?

Answer 1

an increase in population size not an increase in the size of a single bacterium

Question 2

How do bacterial cells replicate?

Answer 2

a form of asexual reproduction called binary fission

Question 3

What is generation time?

Answer 3

time required to complete fission cycle from parent cell to 2 daughter cells. (Doubling time). It is the amount of time needed to double the population.

Question 4

What is the growth rate? What does this vary depending on?

Answer 4

The measure of the length of the generation time environmental condictions

Question 5

What is the generation time of Mycobacterium leprae?

Answer 5

10-30 days (leprosy)

Question 6

What is the generation time of Staphylococcus aureus?

Answer 6

20-30 minutes

Question 7

What 4 phases does a growth curve have?

Answer 7

Lag, Log or exponential, stationary and decline

Question 8

What is a batch culture?

Answer 8

a closed-system microbial culture of fixed volume with limited supplies that aren’t replemished. Cells grown in a closed system have 4 phases: Lag phase, Log or exponential phase, stationary phase and death phase

Question 8

What is the lag phase?

Answer 8

Interval of time between when a culture is inoculated and when growth begins. (not mutiplying as it is aclimitising)

Question 9

What is the expontential phase?

Answer 9

Number of cells doubles during each unit of time.
During exponential growth, the increase in cell number is initially slow but increases at a faster rate

Question 10

What is the stationary phase?

Answer 10

Growth rate of population is zero.
Number new divisions=number of cells dying
Either an essential nutrient is used up or waste product of the organism accumulates in the medium

Question 11

What is the death phase?

Answer 11

Lack of nutrients and increasing accumulation of wastes lead to… number of cell deaths > number of new divisions

Question 12

What is a continuos culture?

Answer 12

an open-system microbial culture of fixed volume

Question 13

What is chemostat and turbidostat?

Answer 13

most common type of continuous culture device

Question 14

What effects the lag phase?

Answer 14

what are the condictions and where the innoculum came from e.g the freezer

Question 15

What is the formula for exponential growth?

Answer 15

N final = (N initial) 2n
N= the number of generations

Question 16

What is cryptic growth?

Answer 16

Growing on dying cells- cells feeding on dying cells 2 expontentail growth periods

Question 17

What is viable count?

Answer 17

It is a direct measurement and the measurement of living and reproducing population. There are 2 main ways to perform plate counts: spread-plate method or Pour-plate method
To obtain the appropriate colony number, the sample to be counted may need to be diluted (serial dilutions)

Question 18

What is filtration?

Answer 18

The process in which solid particles in a liquid or gaseous fluid are removed by the use of a filter medium that permits the fluid to pass through but retains the solid particles

Question 19

What factors affect bacterial growth?

Answer 19

1. availabilIty of nutrients and H2O
2. temperature
3. moisture and drying
4. radiation
   osmotic effects
5. mechanical and sonic stress

Question 20

What is the steady state?

Answer 20

after 5 volume changes inside a bioreacter

the volume is constant and the flow rate is 1 litre per hour

Question 21

What is the diluation rate?

Answer 21

Dilution rate= flow rate / volume

Question 22

What is wash out?

Answer 22

wash out is when the dilution rate is faster than the microorganism growth rate

Question 23

What is total count and viable count?

Answer 23

total count- what u see and visulise

viable count- out of those how many are viable (not dead)

Question 24

Pros and cons of counting chambers?

Answer 24

advantage- easy to use, minimal set up disadvantage- hard to tell if cells are viable or non-viable (don't know if alive or dead)

Question 25

What is serial dilution?

Answer 25

have to diluate samples precisely in a mathmateically way. perfect plate

Question 26

What is the perfect plate with colonies

Answer 26

contains 30-300 colonies

Question 27

Pros and Cons of spreadable agar

Answer 27

agar cheap, used only for counting organisms that resulted in the formation of a colony CFUs colony forming units, but need over night incubation

Question 28

What are indirect methods? and what are some examples?

Answer 28

indictor of microbial presense not looking at counting cells- looking at after effects 1. metabolic activity 2. dry weight 3. turbidity 4.Spectrophotometer

Question 29

What are metabolite examples?

Answer 29

CO2, H2O and any activity envolving metabolism and respiration

Question 30

When is a growth curve obtained

Answer 30

If bacteria counts are made at intervals after inoculation and plotted in relation to time it is obtained

Question 31

what phase are cells in the healthiest state

Answer 31

exponential

Question 32

what do diauxic growth curves have

Answer 32

2 logs

Question 33

what are examples of direct measurements for measuring growth

Answer 33

total cell count, counting chambers, viable count, filtration and most probable number

Question 34

What is total cell count?

Answer 34

direct microscopic examination using special slides, automated counters (flow cytometry)

Question 35

what is the most probable number

Answer 35

a statistical estimating technique

Question 36

What is spectrophotometer

Answer 36

measures the amount of light that passes through a sample. Absorbance is related to the number of bacteria

Question 37

what are looked at for measurements of growth

Answer 37

measurements of cell numbers, cell mass and cell constituants

Question 38

what are used for measurments of cell numbers?

Answer 38

Pore plate, spread plate, membrane filter, plating techniques and direct counting using Petroff Hausseer counting chambers

Question 39

what is used for measurements of cell mass?

Answer 39

dry weight, scattering of light in spectrophotometer

Question 40

what measured in cell constituents?

Answer 40

nucelic acids, chlorophyll, ATP and total protein or nitrogen

Question 41

what are pH of most bacteria

Answer 41

neutrophiles- pH 6.5-7.5 yeast and moulds have a pH of 4-6 some are acidophiles has a pH of less than 4 extremes sulfur oxiddisers can grow to pH 1-2 alkalophiles pH over 9- live in alkaline coils and water up to 11.5

Question 42

what are extremophiles

Answer 42

evolved to grow opitmally under very hot or cold temperatures

Question 43

what are thermophiles

Answer 43

loves heat and high temperatures

Question 44

what are hyperthermophiles

Answer 44

produce enzymes widely used in industrial microbiolgy eg taq polymerase and are very high temperatures

Question 45

what are psychrophiles

Answer 45

low temperature

Question 46

what are psychrotolerants

Answer 46

can grow at 0 degrees but have a optima of 20-40 degrees and are more widely distributed in nature than phychrophiles

Question 47

what are mesophiles

Answer 47

midrange temperature- found in warm-blooded animals, terrestrial and aquatic environments and temperature and tropial latitudes

Question 48

what are barophiles

Answer 48

organisms that live under extreme pressure for their membranes and enzymes depend on this pressure to maintain their 3 dimensional and functional shape

Question 49

what are aerobes

Answer 49

require oxygen to live

Question 50

what are anerobes

Answer 50

do not require oxygen and may be killed by exposure

Question 51

what are facultative organisms

Answer 51

can live with or without oxygen

Question 52

what are areotolerant anareobes

Answer 52

can tolerate oxygen and grow in its presense even though they cannot use it

Question 53

what are microareophiles

Answer 53

can use oxygen only when it is at levels reduced from the air