Colony:

It is the macro scopically visible collection of millions of bacteria originating from a single Bacterial cell.Thus, each colony represent a single bacterium present in the original clinical specimens.

Culture:

It is the term given to the micro organisms that are grown in the laboratory for the purpose of studying them.

Pure culture:

A culture containing only a single species of bacteria is called pure culture.

Culture medium:

It is the term given to the combination of ingredients that supports the growth and cultivation of micro organisms by providing all the essential nutrients required for their growth.

Fastidious bacteria:

A bacterium which exacts in its nutritional needs is called fastidious bacterium.They can grow only when specific nutrients are available.

History:

It was Louis Pasteur who first used an artificial media for the isolation of bacteria.He used urine medium and meat medium for the isolation of bacteria which are liquid medium.later, Robert Koch improvised the media by solidifying it by adding Cooked potato.As the potato is a nutritive substance that can interfere in the growth of micro organisms, started to try gelatin as it is a non nutritive inert substance.However,it was not satisfactory as it liquefies at 24°C.Finally,the agar was introduced as the solidifying agent by Robert Koch.In 1882,Koch reported on the tubercle bacilli and mentioned the new culture medium.In 1887 Julius Richard Petri,a worker in kochs laboratory, modified the flat glass plate into a new type of culture dish for preparation of culture media.It is now called Petri dish.The Petri dish has an overhanging lid to keep contaminants out.

Agar:

Agar is a polysaccharides derived from red seaweed.It is solidification of culture media.It does not have any nutritive value and is not affected by the growth of the bacteria.Agar melts at 98°C and sets at 42°C.About 1.5 to 2 percentage agar is employed in solid medium.

Robertson`s cooked meat medium 

It contains Cooked beef heart.The meat supplies protein,the source of amino acids.It also contains glutathione,a reducing substance that permits the growth of obligate anaerobe.The sulphydryl group, which impart reducing effect, are more available in denatured protein which is available only in Cooked meat.The medium contain dextrose,a source of energy.Growth in this medium is indicated by turbidity or bubble formation by anaerobic bacteria.