Bacterial growth curve

Bacterial growth curve can be divided into four major phase lag phase, exponential phase, stationary phase, decline phase.

Organisms can be grouped as psychrophiles,mesophiles,thermophiles based on their temperature requirements.

Based on oxygen requirements, the bacteria are grouped as obligate aerobe, obligate anaerobe, facultative anaerobe and micro aerophiles.The bacteria that grow better at high CO2 concentration are called capnophiles.

The bacterial growth cycle has four phases.when the bacteria are introduced in the liquid medium and when it is counted at frequent intervals,four different phases can be observed as described in the following subheads

Lag phase

In this phase,no increase in the

Concentration of bacteria is observed.The bacteria will be metabolically active and will be in the process of adaption to the new environment.

Log phase or exponential phase

The log or exponential phase show the steep increase in the concentration of bacteria cell.It is the stage where the bacteria are more susceptible to antibiotics.

Stationery phase

In this phase,due to the nutrients depletion and accumulation of toxic product the cell will start to die.The number of new cell formed will balance the number of cells dead.Hence , the viable count will show a steady state.

Death phase

This phase is marked as the decline of viable count due to lack of new cell formation.The viable cell will start to die due to the lack of nutrients and the toxic production.

Bacteria are unicellular prokaryotic microscopic organisms.The morphology of bacteria like size, shape and arrangements is seen only with the aid of microscope.

There are different types of microscope used to study the morphology of bacteria.They are bright fields microscope,dark field microscope,phase contrast microscope and electron microscope.For most of the microscopic observation, the bacteria have to be stained as they are colourless.There are different staining method.They are simple staining, negative staining, silver impregnation method and differential staining.Bacteria are seen in different shapes like cocci,bacilli,vibrios,spirilla, spirochete and mycoplasma.

Bacteria consist of an outer cell Wall followed by plasma membrane that encloses the cytoplasm and other cellular content.Further,they have appendages like capsule,fimbriae and flagella.

Gram positive cell Wall contain a thick layer of peptidoglycon layer with teichoic acid.The gram negative cell Wall contain thin peptidoglycon layer which is protected further by a lipid rich outer membrane.flagella is explained in first blog.thank you