Chapter 7 second week Flashcards
Microbial Measurement Methods: Direct
- Standard Plate Count
- Direct Observation (Petroff-Hausser)
- Most Probable Number
- Filtration
- Flow Cytometry
Microbial Measurement Methods: Indirect
- Optical density
- Turbidity
- Amount of Metabolic Products
- Dry Weight
Pour Plate Method
- Inoculate empty plate
- Add melted nutrient agar
- Swirl to mix
- Colonies grow in and on solidified medium
Spread Plate Method
- Inoculate plate containing solid medium
- Spread Inoculum over surface evenly
- Colonies grow only on surface of medium
Standard Plate Count Using Serial Dilutions
Direct microbial measurement method
(start with something not dilute and make it dilute; ex of serial dilutions: milk)
-To obtain a countable plate
1. Flask inoculated
2. Samples taken at equally spaced intervals
3. Sample is diluted in liquid agar medium and poured or spread over surface of solidified medium
4. Plates are incubated, colonies are counted
5. Number of colonies (CFU) per 0.1 ml
-Tubes will be increasingly dilute–> less organisms will grow
Serial Dilutions
- 1:10= most organisms
- 1:100= second most
- 1:1000= less organisms, probable count
Direct Microscopic Count Of Bacteria with a Petroff-Hausser Cell Counter
Direct Microbial Measurement Method
-count bacteria individually
-count bacteria in squares when you look under microscope
(you multiply by volume then multiply by ml in test tube)
-every method has drawbacks
Most Probable Number (MPN) Dilution Series
A direct microbial measurement method
A Statistical Estimate
a. MPN (1st set of tubes: 10ml = all 5 positive, 2nd: 1ml= 3 positive tubes, 3rd: 0.1 ml= 1 positive tube out of 5 tubes)
b. MPN Table- enables us to calculate for a sample the microbial numbers that are statistically likely to lead to such a result. ex: the # of positive tubes recorded for each set: 5,3,1; you would then look up that sequence in the table
Filtration
A direct microbial measurement method
(another method for water testing)
a.) the bacteria in 100ml of water were sieved out onto surface of a membrane filter
b.) a filter, with the bacteria much more widely spaced, was placed on a pad saturated with liquid Endo medium, which is selective for gram-negative bacteria. The individual bacteria grew into visible colonies. One hundred twenty-four (124) bacteria per 100ml of water sample
Flow Cytometry
A direct microbial measurement method
- helps come up with a # of bacteria
- requires a computer and a laser beam
- permits reliable detection of single or multiple microbes and can provide info about their distribution within cell population
Spectrophotometer
A Indirect microbial measurement method
- Measures absorbance or optical density (OD) (Light)
- amount of light getting through; more bacteria less light, less bacteria more light
Turbidity
A Indirect microbial measurement method
-cloudiness
Metabolic Activity
(A Indirect microbial measurement method)
Assumes the amount of metabolic product such as CO2 or acid or alcohol is in direct proportion to the number of bacteria present
-Product amount= # of bacteria
Dry Weight
(A Indirect microbial measurement method)
Best method for filamentous bacteria (e.g. Actinomyces) or molds
-The weight or mass of organic matter or soil after removal of water by heating to constant weight
-The dry weight of cells is the weight left when their water content has been removed by heating
Microbial Associations
- Symbioti
- Nonsymbiotic
