Microbiology and Immunology

Growth and growth media WORLD OF MICROBIOLOGY AND IMMUNOLOGY

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The chemical make-up of the cell wall also determines

the penetrability of the wall by various drugs. Knowing if a

bacterium is Gram positive or negative determines what type

of antibiotic is suitable for treatment, as some antibioticsact

against Gram positive bacteria (i.e., penicillin), while others

act against Gram negative bacteria (i.e., tetracycline or strep-

tomycin). Another important consideration is the fact that

some Gram negative bacteria release endotoxins, which can be

fatal. When pharmaceutical companies develop new antibac-

terial drugs, the Gram stain is the method by which scientists

determine the effectiveness of the drug.

See alsoLaboratory techniques in microbiology

GRAMICIDIN•seeANTIBIOTICS

GREEN FLUORESCENT PROTEIN• see

LABORATORY TECHNIQUES IN IMMUNOLOGY

GGrowth and growth mediaROWTH AND GROWTH MEDIA

The ability of all organisms, including microorganisms, to

grow and divide is the fundamental underpinning of their con-

tinued existence. In the laboratory, the nutrients needed for

growth are supplied in the form of growth media.

Microorganisms such as bacteria, yeast, and algae grow

by increasing in size, replicating their genetic material and

other internal factors such as proteins, manufacturing the

required additional cell wall material to enclose the new cell,

and finally dividing to form two so-called daughter cells. Vital

materials are required by most microbes, including carbon,

hydrogen, nitrogen, phosphorus, calcium, cobalt, magnesium,

and manganese. Often these elements must be supplied in the

growth media, because the microbes cannot manufacture

them. Once supplied, however, such elements form the build-

ing blocks upon which the microorganism can construct some

(but not all) amino aids, proteins, and even the DNA (deoxyri-

bonucleic acid) and ribonucleic acid(RNA) genetic materials.

Provision of the necessary elements is not sufficient to

permit growth, however. The level of oxygen, moisture con-

tent, and temperature are examples of other factors that must

be adjusted to permit the growth of the target microbe. For

example, Escherichia colirequires a temperature of around

Growth of virus creates clearing in lawn of growing Escherichia coli.

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