A drop of the culture of bacterial suspension is placed on a coverslip. Vaseline is placed near the concave area of the slide approximately the corners of the coverslip. The slide is placed over the coverslip so that his drop of culture is directly under the concave area and the Vaseline adheres to the coverslip.
The slide is then quickly inverted and placed under the microscope. Motile organisms will be seen darting through the medium in which they are suspended. Motility should be differentiated from Brownian movement which is caused by bombardment of the molecules of the fluid. In motility the organisms move in a definite direction whereas in Brownian movement they show no direction.
A wide variety of procedures and nutrient preparations are used to induce micro-organisms to grow and reproduce. Different microbes require different environments and nutrients, called culture media (singular, medium).
For instance, procedures for culturing fungi are little value in inducing viruses to grow. Microorganisms are usually cultivated in containers, including test tubes, flasks, Petri dishes, and even huge steel tanks.
The tanks are employed commercially to obtain large quantities of the desired organisms or their products. Whatever the actual container material may be the procedures are referred to as in vitro-literally, “in glass” even though such containers are often made of plastic.
Some microorganisms cannot be grown in vitro, but only in living animals. Cultivation methods using live animals are called in vivo techniques. When animal tissues are removed and used as a culture medium for microbes, the procedure is an in vitro one because a culture vessel is used, not the living (vivo) animal.
Some microbes can be cultured both in vivo and in vitro. Extensive and intensive studies of the particular requirements of different microorganisms have led to the development many culture media and techniques. Modifications and improvements continually appear, as knowledge increases.
This chapter deals with the general requirements for life of microorganisms. In order for organisms to cause disease, it must be able not only to survive, but to grow and reproduce in or on the body of its host.
These pathogens-as well as nonpathogenic microbes that populate different body regions-carry on their life processes in environments containing different organic and inorganic substances, oxygen and carbon dioxide concentrations, and alkalinity or acidity (pH).
Cultivation techniques and media used to provide suitable conditions for the growth of bacteria and fungi will be discussed from this viewpoint.
Topics will be handled in the following order:
1. Forms of nutrition;
2. Physical requirements for growth;
.3. Properties of bacteriological media;
4. Selected media and their ingredients;
5. Preparation of media;
6. Techniques of inoculation and isolation of pure cultures;
7. Conditions of incubation;
8. Use of sterility cabinets; and
9. Media and techniques for the cultivation of fungi.