Chapter 6 - Microbes & Media

Front 1

Culture medium

Back 1

Nutrient material prepared for growing microorganisms

Front 2

Inoculation

Back 2

Introduction of a microorganism into medium.

Front 3

Culture

Back 3

Growth of a Microorganism observed on/in a medium.

Front 4

Chemically defined media

Back 4

Media when exact composition known

Front 5

Complex media

Back 5

Media when exact composition varies

Front 6

Selective media

Back 6

Media that favors the growth of desired microorganisms and inhibits the growth of unwanted ones.

Front 7

Differential media

Back 7

Media that distinguishes between groups of microorganisms.

Front 8

MacConkey's Agar

Back 8

Selective medium
1. Inhibits gram-positive bacteria
2. Encourages gram-negative bacteria.

Differential medium
1. Lactose fermenters produce acid and form pink colonies
2. Non-lactose fermenters form colorless colonies

Front 9

Blood agar

Back 9

Differential media made from 5% sheep blood and the microorganisms change the color of the medium.

Front 10

Microbial Growth

Back 10

Refers to the increase in number of cells not the size of individual cells.

Front 11

Generation time

Back 11

The time required for a bacterial population to double (usually 1-3 hours)

Front 12

Generation number

Back 12

Expressed as a power of 2

Front 13

Closed systems
Batch culture

Back 13

1. Lag phase: first generation growth time
2. Log phase: exponential growth time
3. Stationary phase: cells are dying as fast as they are growing
4. Decline phase: cells are dying faster than they are growing

Front 14

1. Build up of toxic waste
2. Use up nutrients in a closed system

Back 14

Why closed systems always decline

Front 15

Continuous cultures

Back 15

Open systems

Front 16

Direct Methods

Back 16

1. Viable plate count
2. Membrane filtration
3. Microscopic count
4. Most Probable Number (MPN)
5. Electronic counters

Front 17

Indirect Methods

Back 17

1. Turbidity
2. Metabolic activity
3. Weight

Front 18

Viable Plate Count

Back 18

1. Limit CFUs to 30-300
2. Uses serial dilutions

Advantages:
only living cells

Disadvantages:
Incubation time
Growth requirements
May underestimate count

Front 19

Plate count methods

Back 19

1. Pour-plates (Good spread of microbes but its hot and can kill them)
2. Spread plates (Not hot but doesn't spread well)

Front 20

Membrane Filtration

Back 20

1. Liquid pass through filter
2. Filter placed on solid medium
3. Organisms on filter will grow

Advantages:
Only living cells
Can be used to count low cell concentrations

Disadvantages:
Must used at least 100 mL of media
Incubation time
May underestimate count

Front 21

Microscopic Count

Back 21

1. Known volume of sample placed in counting chamber
2. Viewed under microscope
3. Cells counted

Advantages:
No incubation time

Disadvantages:
Dead cells maybe be counted
Tedious
Requires high concentration of cells (10 million per mL)

Front 22

Most probable numbers (MPN)

Back 22

1. Multi-tube statistical assay
2. Liquid media only
3. Each tube diluted with 10x less sample than previous

Advantages:
Measure only living cells
Useful for culturing cells that wont grow on solid media

Disadvantages:
Incubation time
Expensive and time consuming

Front 23

Electronic Counter

Back 23

Coulter counter - electrical current
Flow Cytometry - light transmission

Advantage:
No incubation time

Disadvantage:
Dead cells may be counted
Not very sensitive due to clumping and other debris in media

Front 24

Turbidity

Back 24

1. Uses spectrophotometer
2. Measures light transmitted through sample

Advantages:
No incubation time

Disadvantages:
Must have high concentration of cells
May count dead cells

Front 25

Weight

Back 25

Wet weight - cells centrifuged and packed cells weighed
Dry weight - packed cells dried at 100 degrees C for 8 to 12 hours then weighed

Advantages:
Useful in measuring filamentous organisms

Disadvantages
Tedious and time consuming
Not sensitive enough
Dead cells weighed

Front 26

Metabolic Activity

Back 26

Based on enzyme activity

Advantages:
Once metabolic rate is established it provides reliable estimate of cell number

Disadvantages:
Incubation time
Requires metabolic rate to be established in advance