1. lag phase

        2. exponential (log) phase

        3. stationary phase

        4. death phase
 

II. Measurement of Microbial Growth

    A. Measurements of Cell Numbers

        1. Counting chambers (Petroff-Hausser)

            counting grid

            advantages

            disadvantages
 

        2. Electric cell counters

            used for larger cells

            electric current or laser
 

        3. Plating techniques

            dilute sample to get 25-250 colonies per plate

            can use a calibrated loop
 

        4. Membrane filters

            trap microorganisms on a filter then culture
 

        1. Dry weight
 

        2. Turbidity measurements

            measure light scattering in a spectrophotometer
 
         3. Cellular constituent measurement

        sterile medium added at a constant rate that is equal to medium containing microorganisms that is removed

    B. Turbidostat

        measures turbidity of growth vessel which determines flow of new medium
 

        microorganims have a semi-permeable membrane and can be affected by changes in osmotic pressure

        hypotonic solutions

        hypertonic solutions

        water activity (aw): degree of water available

        osmotolerant

        halophiles
 

    B. pH

        measure of hydrogen ion (H+) concentration

        scale goes from 0.0 (1 M H+) to 14.0 (1 x 10-14 M H+)

        acidophiles

        neutrophiles

        alkalophiles
 

    C. Temperature

        2. Classification of microorganisms by optimal temperature

            a) psychrophiles: optimal about 15^oC

            b) psychrotrophs: optimal between 20-30^oC

            c) mesophiles: optimal between 20-45^oC

            d) thermophiles: optimal between 55-65^oC

            e) hyperthermophiles: optimal between 80-110^oC
 

    D. Oxygen Concentration

        1. Classification of microorganisms by oxygen requirement

            a) obligate aerobes: e.g. Mycobacterium sp.

            b) facultative anaerobes: e.g. Staphylococcus sp.

            c) aerotolerant anaerobes: e.g. Streptococcus sp.

            d) obligate (strict) anaerobes: e.g. Clostridium sp.

            e) microaerophiles: e.g. Campylobacter sp.
 

        2. Toxic forms of oxygen

            superoxide radical O₂^-

            hydrogen peroxide H₂O₂

            hydroxyl radical OH^-
 

        4. Cultivation techniques

            a) obligate aerobes
 

            b) obligate anaerobes

                1) broth with reducing agents: thioglycollate or cysteine

                2) gas-pak jars and bags

                3) anaerobe hood
 

    E. Pressure

        most microorganisms exposed to only 1 atm of pressure

        barotolerant

        barophilic