M2/L1: BACTERIAL GROWTH

MICROBIAL GROWTH

Refer to the increase in the number of cells, not the size of the cells

BINARY FUSION

Most bacterial cells reproduce by an asexual process

GROWTH

the orderly increase in the sum of all the components of an organism

BUDDING

how some bacteria reproduce

TRUE GROWTH

increase in population/number of cells

EXPONENTIAL GROWTH

Bacteria are said to undergo exponential growth or logarithmic growth

GENERATION TIME

• The time required for a cell to divide and its population to double.

• Bacteria reproduce by binary fission, and the average time required for the population, or the biomass, to double is known as the generation time or doubling time.

• Generation time varies on the organism

  • Not all organisms divide in 20 minutes

E COLI

shortest generation time, divides at 15 minutes

MYCOBACTERIUM TUBERCULOSIS

slow generation time

GENERATION TIME

FORMULA FOR GENERATION TIME

INCUBATION PERIOD

The time when microorganism is acquired until the appearance of first symptoms

Lag phase

exponential phase

stationary phase

death phase

PHASES OF GROWTH

LAG PHASE

• Little or no cell division occur

• Bacterial cells adapting to their new environment

• Bacteria undergo period intense metabolic activity

• NOT DORMANT

• GROWTH RATE: zero

EXPONENTIAL PHASE

• aka Log Phase

• The stage where most bacterial cells are most metabolically active.

• Where binary fission happens

• the cells are in a steady state and grow

• GROWTH RATE: constant

STATIONARY PHASE

• Period of equilibrium

• Number of microbial deaths = number of new cells

• As they increase, there is little nutrients

• The number of deaths will be balanced

• Eventually, the exhaustion of nutrients or the accumulation of toxic products causes growth to cease completely

• There is a slow loss of cells through death, which is balanced by the formation of new cells through growth and division

• GROWTH RATE: zero

DEATH PHASE

• Period of decline

• Number of microbial deaths > number of new cells

• After a period of time, cell viability begins to decrease at a defined rate

• A bacterial phenomenon referred to as viable but not culturable (VBNC) cells, is thought to be the result of a genetic response triggered in starving, stationary phase cells

• GROWTH RATE: negative (death)

GROWTH CURVE