Microbial growth.

Microbial growth.

1. Is defined as an incerease in the number of cells in a population.

   • THE CONCEPT OF EXPONENTIAL GROWTH.
     • During cell division one cell becomes two.
       • Generation time.
         • Vary widely among microorganisms. Is dependent on the growht medium and the incubation conditions used.
           • THE MICROBIAL GROWTH CYCLE.
             • Lag Phase.
               • Microbial culture is inculated into a fresh medium, growth usually begins only after a period of time.
                 • This interval may be brief or extended, depending on the history of the inoculum an the growth conditions..
             • Exponential Phase.
               • Each cell divides to form two cell, each of which also divides to form two more cells.
                 • The rate of exponential growth is influenced by enviromental conditions.
             • Stationary Phase.
               • In these phase, there is not net increase or decrease in cell number and thus the growth rate of the population is zero.
                 • The population may not grow during these phase, many cell functions can continue, including energy metabolism and biosynthetic processes.
             • Death Phase.
               • The cell may remain alive and continue to metabolize, but they will eventually die.
                 • The rate of cell death is much slower that the rate of exponential growth.
     • Exponential Growth.
       • Population increase, where the number of cells doubles during a constant time interval.
         • Straight - line fuction.
           • Reflects the fact that the cells are growing exponentially and the population is doubling in a constant time interval.
           • THE MATHEMATICS OF EXPONENTIAL GROWTH.
             • Relationship exists between the initial number of cells and number present after a period of exponential growth.
               • N=N02^n
                 • N= final cell number. N0= initial cell number. n= no. of generations during the period of EG.
     • Consequences of exponential growth.
       • In an actively growing bacterial culture, cell numbers can get very large very quickly.
         • Exponential growth for nonsterile and nutrient-rich food product such as milk leads to spoilage.