Fundimental of microboilogy Term Paper Example | Topics and Well Written Essays - 1500 words

Fundimental of microboilogy - Term Paper Example The catalase test is a biochemical test that can be used to identify between Staphylococcus spp. and Streptococcus spp. The enzyme catalase contains a heme group and detoxifies hydrogen peroxide. The basic theory used in their identification is that one is catalase positive (Staphylococcus spp.) while other one (Streptococcus spp.) is catalase negative. If gas formation (O2) is observed in the form of bubbles, then it ensures that the sample of bacteria has a catalase; it is an indication of presence of Staphylococcus spp. Otherwise, on no gas formation, the sample contains Streptococcus spp. Non-selective medium is employed when organisms are present in low numbers. This also provides an indication about the type of organism present in the sample. The use of selective medium is to isolate the desired organism present in the mixed sample Nutrient agar is ideal as a non-selective culture medium to grow a large variety of microorganisms. In order to isolate microorganism from the agar plate, the part of colony is taken to a new agar plate. The streak-plate method can be employed as it reduces density of the microorganisms on the surface of the agar. This facilitates to obtain the distinct colonies of the microorganisms of our interest by using selective media (Selective and Differential Media 2012) Selective media inhibit the growth of some organism while promote growth of others. Selective inhibition is done by adding salts, dyes or specific inhibitors affecting the metabolism of the organisms. Crystal violet or penicillin will inhibit the growth of Gram-positive bacteria. Based on this philosophy, Tellurite agar is employed as media to identify for Gram-positive organisms. When gram negative organisms are to be selected or identified, the agar with penicillin (5-50- units/ml) is used (Selective and Differential Media 2012). Selective but differential media are