growth of bacteria

Question 1

what are four methods to estimate the growth of a bacterial culture

Answer 1

1. Haemocytometer
2. Turbidity
3. Dilution plating
4. Dry mass

Question 2

Describe how to conduct haemocytometer ?

Answer 2

1. Dilute broth sample with equal volume of trypan blue to stain dead cells
2. Use a calibrated haemocytometer with volume 0.1mm3. Count the cells in each of the sets of 16 squares and calculate means
3. Number of bacterial cells = number counted x 10 to the power of 4 per cm3

Question 3

Is haemocytometer viable count or total count ?

Answer 3

total

Question 4

does haemocytometer count the exact no. of cells ?

Answer 4

yes - human error

Question 5

how fast is the haemocytometer ?

Answer 5

slow

Question 6

what are the uses of haemocytometer ?

Answer 6

bacteria

Question 7

explain how to conduct a turbidity ?

Answer 7

1. Use colorimeter. Measure absorbable or % transmission of samples of known microorganism counts
2. Plot calibration curve
3. Record absorbable/ % transmission of unknown sample. The cloudier, the less light is absorbed. Plot graph

Question 8

Is turbidity viable count or total count ?

Answer 8

total

Question 9

does turbidity count the exact no. of cells ?

Answer 9

no

Question 10

how fast is the turbidity ?

Answer 10

fast

Question 11

what are the uses of turbidity ?

Answer 11

bacteria

Question 12

explain how to conduct dilution plating

Answer 12

1. Start with 10cm^3 of undiluted culture
2. Add 1cm^3 of first tube into 9 cm^3 of sterile saline
3. Continue to add 1cm^3 from previous tubes to form serial dilutions

Question 13

why is appropriate dilution a compromise when diluting a culture?

Answer 13

Must have a low enough number of microorganisms to count and a high enough number to provide a reliable sample of the culture

Question 14

is dilution plating viable or total count ?

Answer 14

viable

Question 15

does dilution plating give the exact no. of cells ?

Answer 15

yes - human error

Question 16

how fast is dilution plating ?

Answer 16

very slow

Question 17

what are the uses of dilution plating ?

Answer 17

bacteria

Question 18

how is dry mass conducted >

Answer 18

a known volume of culture can be dried and weighed to find the bacterial cell

Question 19

is dry mass viable or total count ?

Answer 19

total

Question 20

does dry mass give the exact no. of cells ?

Answer 20

no

Question 21

how fast is dry mass ?

Answer 21

slow

Question 22

what are the uses of dry mass ?

Answer 22

moulds

Question 23

whare the phases in a bacterial culture ?

Answer 23

lag phase
log phase
stationary phase
death phase

Question 24

explain the growth in lag phase

Answer 24

• slow growth as bacteria prepare to use nutrients available, which may involve activating genes or producing enzymes

Question 25

explain the growth in log phase

Answer 25

growth is exponential with rapid doubling of numbers the y axis of the graph is logarithmic so the change appears as a straight line

Question 26

explain the stationary phase

Answer 26

death rate equals division rate due to a build up of waste and lack of nutrients

Question 27

explain the death phase

Answer 27

population of live cells falls because death exceeds new cell production as conditions continue to deteriorate