What are the traditional detection methods of microorganisms?

What are the traditional detection methods for direct observation of microorganisms by microscope? Generally speaking, under certain culture conditions (the same culture medium, temperature and culture time), the same microorganism shows stable colony characteristics. These characteristics include the shape, size, bulge degree and color of colonies. Therefore, the species of microorganisms can be judged by observing the characteristics of colonies under a microscope. Use selective culture medium to cultivate microorganisms or artificially provide conditions conducive to the growth of target strains.

Selecting culture medium, as its name implies, is to allow some kinds of microorganisms to grow, while inhibiting or preventing the growth of other microorganisms. For example, microorganisms that can synthesize urease can be cultured in a medium with urea as the sole nitrogen source; Adjusting the PH in the culture medium to acidity is beneficial to the growth and reproduction of mold (inhibiting the life activities of bacteria) and so on. Selective culture is generally judged indirectly by observing the assimilation type or a certain characteristic of microorganisms. There is often not only one kind of microorganism, and the characteristics of these microorganisms can be roughly determined for classification.

Use identification media. That is to say, according to the metabolic characteristics of microorganisms, some indicators or chemicals are added to the culture medium. For example, the detection of Escherichia coli in water quality inspection (the number of Escherichia coli is used to measure the pollution degree of feces to water) uses eosin-methylene blue reagent, which reacts with Escherichia coli in water or dairy products, showing dark purple and metallic luster, belonging to the characteristic reaction of Escherichia coli. Compared with selective culture, the range of identification results of identification medium is relatively small, and the species of microorganisms can usually be directly determined.