from the results, about how many organisms/ml can be in a clear broth without showing any sign of turbidity?
MANY
what are two sources of error in this procedure?
There are many potential sources of error. Examples include: incorrect measuring of the sample or diluent; insufficient mixing; not switching pipettes between each step of the serial dilution; contamination because of poor sterile technique; or inadequate
if you serially dilute a sample with three 1:10 dilutions, what is the dilution of the last tube?
10-3
if you add 1.0ml to 99ml of water, what is the dilution of the sample?
10-2
if you had a solution containing 6000 organisms/ml, how could you dilute and plate a sample so that you had a countable plate?
A common answer to this question is as follows:
1. Add 1.0ml of the original broth culture to 9.0ml water (to obtain a 10-1dilution). The 10-1 dilution will have 600 cells/ml.
2. Add 1.0ml of the 10-1 dilution to 9.0ml water (to obtain a 10-2 dilution). T
serial dilution
preparing a dilutin in steps instead of one dilution
turbidity
cloudiness
viable (bacteria)
capable of growing and dividing
Plate count
each viable bacterium produces a colony when growing on an agar plate. ideal number of colonies on plate is 30-300.
direct count
bacteria put on a slide with squares that has been designed to hold a specific volume of liquid. faster than a plate count but there have to be about 1x107 organisms/ml and both viable and nonviable organisms appear.
turbidometric method
spectrophometer measures turbidity. must first correlate optical density (O.D.) with plate counts.
new pipet
must be used for each transfer between a more concentrated solute and less concentrated solute.
TNTC
too numerous too count=more than 300.
dilution =
sample ml / (sample ml+dilutent ml)
the # of organisms/ml in the original suspension=
# of organisms on the plate x 1/sample vol x 1/dilution