Microbial Growth and Multiplication

Bacterial Reproduction
PHASES OF GROWTH
*picture on pg. 339
-LAG PHASE
-LOG PHASE
-STATIONARY PHASE

-DIE OFF

Bacterial Reproduction
GENERATION TIME

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As mentioned above, bacterial growth rates during the phase of exponential growth, under standard nutritional conditions (culture medium, temperature, pH, etc.), define the bacterium’s generation time. Generation times for bacteria vary from about 12 minutes to 24 hours or more. The generation time for E. coli in the laboratory is 15-20 minutes, but in the intestinal tract, the coliform’s generation time is estimated to be 12-24 hours.

Calculation of Generation Time

When growing exponentially by binary fission, the increase in a bacterial population is by geometric progression. If we start with one cell, when it divides, there are 2 cells in the first generation, 4 cells in the second generation, 8 cells in the third generation, and so on. The generation time is the time interval required for the cells (or population) to divide.

G (generation time) = (time, in minutes or hours)/n(number of generations)

G = t/n

LAG PHASE
the Lag Phase is the most important phase that must be c.Onsidered in the
bacterial growth phase. The lag phase yields a certain time before the bacteria starts to multiply rapidly.
The goal of food preservation is to extend the lag phase for as long as possible. The theory is not to fight
contamination, but to extend the lag phase by preventing bacteria from multiplying (except for certain
pathogenic bacteria such as typhoid and cholera where prevention from contamination is of the utmost
importance due to the potency of the bacteria). During the lag phase, some of the bacteria die off because it cannot handle the environment.
LOG PHASE
A slight
decline of bacteria on the graph is shown before the Log growth phase. Multiplication of the bacteria is
exponential, it doubles itself each time, many times over each hour before reaching a stationary plateau.
STATIONARY PHASE
In the Stationary Phase, environmental conditions and food sources may start to become restrictive
resulting in an leveling of bacterial growth.
DIE OFF
As the graph falls into the Death Phase, bacteria start
producing waste products and toxins which kill each other off but not all bacteria are killed. Slowly they
die off. After the food is so decomposed only certain micro-organisms break down the foods. This
completes the perfect bell shaped curve in the cycle of the growth of bacteria
BACTERIA GROWTH FACTORS DEPEND ON:
1. Food source.
2. Acidity (pH factors; also basicity).
3. Time.
4. Temperature
5. Oxidation reduction potential.
6. Moisture (must be at least 18%, (refer to Water Activity in this manual).
REMEMBER THE ACRONYM “FATTOM”