Exercise 13 - Enumeration Of Bacteria

Question 0

Dilution factors of bottle B’s 1ml and .1ml plates

Answer 0

1ml = 10^4

.1ml = 10^5

Question 1

Serial dilution procedure

Answer 1

Take 1ml from the culture and transfer to bottle A

Transfer 1ml from bottle A to bottle B

Transfer .1 ml to a petri, as well as 1ml to another Petri from bottle B

Transfer 1ml from bottle B to bottle C

Transfer .1ml to a petri, as well as 1ml to another petri from bottle C

Question 2

Dilution factors of bottle A’s 1ml and .1ml plates

Answer 2

1ml = 10^6

.1ml = 10^7

Question 3

What is the correct plate to count

Answer 3

30 - 300 colonies

Question 4

Direct counting methods advantages and disadvantages

Answer 4

Advant - count only live cells (viable)

Disadvantages - requires incubation time

Question 5

Be able to calculate number of organisms per ml in original culture from the appropriate plate

Answer 5

(The # of organisms in correct plate) x 10^7

Then convert to scientific notation

Ex. 45 x 10^7 = 4.5 x 10^8 cfu/ml

Question 6

Turbidity

Answer 6

Cloudiness, measured as Optical Density OD

Question 7

Advantages and disadvantages of indirect counting method

Answer 7

Advant- quick, no incubation time

Disadvant- counts live + dead cells

Question 8

OD =

Answer 8

OD = 2-log%T

Question 9

Steps for calibrating spec 20, and measuring % transmittance

Answer 9

Set the wavelength to 686

Select transmittance mode

Zero it out

Insert calibrating cuvette

Adjust transmittance to 100%

Remove calibrating cuvette

Insert bacterial cuvette, read % transmittance

Question 10

High % transmittance =

Answer 10

Low growth