types of media

• undefined
• defined
• differential 
• selective
• solid
• liquid
• batch culture

undefined media

• a medium ehre the chemical composition is not known

defined medium

• a medium where the exact chemical composition is known

differential media

• a type of medium that has an indictor, usually a dye
• the dye changed color if a reaction occurs
• example - protease detection plates

selective media

• a type of differential media
• contains compounds that inhibit the growth of some organisms, but not others

solid media

• immobilizes cells and causes them to form colonies
• size, shape, and color can be examined

batch culture

• an organism is grown in an enclosed vessel (tube/flask)
• has four phases
• 1. lag
• 2. exponential
• 3. stationary
• 4. death 

exponential growth

• constant doubling of the cell count during a constant time interval
• represented by a graph with continously increasing slope
• when plotted (as log functions) looks like a straight line

direct count

• count done under a microscope 
• easy and simple to do
• cannot distinguish live cells from dead cells
• small cells are hard to see
• need phase contrast if you dont use a stain
• motile cells must be immobilized
• can mistake debris on the slide as a cell 

optical density

• measure of the turbidity (how dense the liquid looks)
• measure of the light scattered by a liquid culture
• increase with an increase in cell number

viable count

• measures the cells in the culture that are capable of reproducing
• uses the spread-plate or pour-plate method
• mistakes in counting can be made
• increase incubation can increase cell count
• can be plating inconsistencies 

n = t/g

• n = number of generations
• t = time
• g = generation time

chemostat

• continuous culture device, or an open system
• fresh medium is added at a constant rate as the spent culture is removed
• steady state - when the volume, cell number, and nutrient status remain constant at equilibrium 

factors that affect growth rate and cell density

• dilution rate
• concentration of a limiting nutrient

cardinal temperatures

• minimum, optimum, and maximum temperatures at which an organism can grow

psychrophile

• ~0-10 C

mesophile

• ~10-50 C

thermophile

• ~40-70 C

hyperthermophile

• ~65-110 C 

neutrophils

• like neutral pH values
• ~7 pH
• example - E. coli

acidophiles

• ph < 5.5

alkaliphiles

• pH > 8.0

aerobes

• obligate - need O2
• facilitative - not needed, but grows better with O2
• microaerophilic - required, but at low levels

anaerobes

• obligate (strict) - cells die in the presence of O2
• aerotolerant / facilitative - not required, but can use is 

toxic forms of oxygen 

• O2
• H2O2
• OH-
• adding an enzyme can remove toxic forms of oxygen