Microbio Lab 6 Flashcards
microscopic counts
diluted and counted with microscope
most probable number (MPN)
the number of bacteria in a sample can be determined by the relationship of some growth parameter to statistical probability
standard plate count (SPC)
A sample is diluted and then plated; the colonies are counted after incubation; the original number is determined by multiplying the number of colonies by the dilution factor; based on each colony arising from one cell
coliforms
indicator bacteria found in the intestines of humans and warm-blooded animals, ferment lactose to produce acid and gas; presence suggest the potential for disease
colony forming units (CFUs)
the number of colonies (arising from one or more cells); only numbers between 30-300 are considered statistically valid
turbidity
cloudiness of medium; can be related to growth and concentration
optical density/absorbance
Uses light scattering to determine size of a microbial population
Why is CFU more applicable to a culture of Streptococcus than to a culture of E. Coli?
Streptococcus are in chains and multiple cells may make up a colony so it is more necessary to use CFU with streptococcus than E. Coli which does not form chains.
How would you inoculate a plate to get a 1:10 dilution? a 1:100 dilution?
for a 1:10 dilution, plate 0.1 ml.
for a 1:100 dilution, transfer 1ml into 9ml water, and plate 0.1 ml
Why is it necessary to perform a plate count in conjunction with the turbidimetry procedure?
A plate count gives the number of colonies and turbidimetry measures the density of the colonies
For the following methods of bacterial enumeration, does the method determine total count or viable count?
a. MPN
b. Microscopic count
c. standard plate count
d. turbidity
a. MPN - viable
b. microscopic count- total
c. standard plate count- viable
d. turbidity - total
enriched media
compounds are added to further supplement the nutrients in complex media for fastidious organisms (whole blood, serum, plasma, vitamins, and specific amino acids)
autoclave
huge pressure cooker, 121 ºC, 15psi, 15 min, most media
baking
oven, dry heat, 180º C for 2-3 hours, glassware
filtration
filter, heat labile solutions
