Page 71 - MNU microbiology theoritical 2025

General Microbiology & Immunology (PM 401) Second level Semester 4 2024/2025

3- Stationary phase

• In a closed culture, food soon runs out or the organisms become poisoned by their

own accumulated waste

• In this phase, the number of new cells created by cell division is now equivalent

to the number of cells dying; thus, the total population of living cells is relatively

stagnant.

4- Death Phase (decline phase)

As a culture medium accumulates toxic waste and nutrients are exhausted, cells die

in greater and greater numbers. Soon, the number of dying cells exceeds the number

of dividing cells, leading to an exponential decrease in the number of cells

Measurement of death rate

• A death curve can be plotted of log no. of surviving cells versus time and the

curve will be a straight line.

• The slope of the straight line represents the death rate.

Sustaining Microbial Growth

• The growth pattern takes place in a closed environment; nutrients are not added
and waste and dead cells are not removed.

• In many cases, though, it is advantageous to maintain cells in the logarithmic
phase of growth.

• One example is in industries that harvest microbial products.

General Microbiology & Immunology (PM 401) theoretical handbook Page 60