Effect of Nutrient Compositionon Food Microbes

Microbes also need nutrients for their growth. Culture medium usually contains nutrients which are essential for their well growth. In a culture medium there are carbon source, nitrogen source (organic source), macronutrients, micronutrients, growth factors. Gelling agents, antibiotics and dyes usually need in order toculture microorganisms.

Especially for heterotrophs a carbon source is an essential requirement. Hence depending on the microorganism that is growing in the culture medium, we must adjust the nutrient requirement. Nitrogen source can be inorganic or organic. Organic source include starch, glucose, sucrose, fructose etc. Macronutrients include Sulfur (S), Magnesium (Mg), Calcium (Ca), Potassium (K), Chlorine (Cl). Some of the micronutrients are Zinc (Zn), Manganese (Mn), Copper (Cu). Growth factors usually added are vitamins, pirins, pirimidins etc.

Gelling agents are agar and gelatin.Agar is made out of red algae. Melting point is 850C. It is a complex mixture of polysaccharides extracted from red algae. Red algae are a group of microorganisms. Usually used red algae are Gelidium andGracillaria. Agar is insoluble in cold water and dissolved in hot water. It usually sets in between 320C to 390C.

Gelatin is made out of hooves of animals. Therefore this is high in protein. Melting point is very low compared to agar. Melting point is 300C to350C. Integrating temperature is around 200C to 250C. Thus it limits the usage. This is readily digested by some bacteria.

Antibiotics generally included before pouring into plates to inhibit specific groups of microorganisms. Streptomycin is heat resistance and thus added before heating. Penicillin is heat sensitive, hence added after heating.


Dyes are generally thermo stable. Usually added before autoclaving. Rose Bengal, Brilliant green, Crystal violet are some of the dyes used in culturing.

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