Lab 13

Front 1

Methods of estimating bacteria in a broth culture

Back 1

-Standard plate count
-Direct microscopic count
-Turbidimetric measurement
-Cell mass determination
-Cell activity measurement
-Particle counts
-Visual comparison of turbidity

Front 2

Standard Plate Count
(counts viable cells)

Back 2

-Diluted culture plated on spread plate/ pour plate
-Count colonies per mL with Quebec counter

Front 3

Turbidimetric Method
(counts large # of cells)

Back 3

-use turbidimeters/ spectrophotometers
-compare turbidity of different concentrations with standard plate count

Front 4

Spectrophotometer

Back 4

Determines the light absorption properties of a molecular species in solution

Front 5

Determination of Bacteria Concentration (non-dissolved particles)

Back 5

Measure light lost through absorption and light lost through scatter

Front 6

Initial Spectrophotometer settings

Back 6

100% Transmittance
0% Absorbance

A = Optical Density = 2 - log(%T)

Front 7

Light Wavelength

Back 7

420nm - clear solution
540nm - light yellow
600-625nm - yellow to brown

Front 8

Direct Microscopic Count
(practical with large number of cells)

Back 8

-0.01mL of bacterial suspension is spread over 1cm^2 area on a glass slide.
-slide is dyed
-organisms are counted and average number of cells per field is calculated

Front 9

# of Bacterial cells/ mL =

Back 9

(area of smear/ area of field) x (average #cells/field) x (#samples/ mL)

Front 10

McFarland Standards

Back 10

-Compare sample to Standards
-Prepared by adding 1% BaCl2(aq) and 1% H2SO4(aq)
-Gives turbidity corresponding to an approximate bacteria density