Aseptic Technique and Transfer of Microorganisms

Topics: Agar plate, Petri dish, Agar Pages: 8 (2389 words) Published: July 10, 2012
Microbes, also called microorganisms, are minutes living things that individually are usually too small to be seen with the unaided eye. The group includes bacteria, fungi (yeast and molds), protozoa and microscopic algae. It also includes viruses, those noncellular entities sometimes regarded as straddling the border between life and nonlife. People tend to related these microbes only with major disease such as AIDS, uncomfortable infections, or such common inconveniences as spoiled food. However, the majority of the microbes play important role by helping to maintain the balance of living organisms and chemicals in our environment. Though only a minority of microbes are pathogenic (disease-producing), practical knowledge of microbes is necessary for medicine and the related health sciences (Tortora, Funke, Case, 2010, p.2).

Microbial growth is referring to the growth of cell in terms of number of cells, not the size of the cells. Microbes that are “growing” are increasing in number, accumulating into colonies (groups of cells large enough to be seen without a microscope) of hundreds of thousands of cells or populations of billions of cells (Tortora, Funke, Case, 2010, p.157). Although microbes can be found everywhere around us, such as soil, water, food, sewage, body surfaces and also air, but to grow microbes is laboratory for research purpose, different microbes may have different growth requirement. A nutrient material prepared for the growth of microbes in a laboratory is known as the culture medium. Some bacteria can grow well on just about any culture medium while the other required special media, and still others cannot grow on any nonliving medium yet developed. Microbes that are introduced into a culture medium to initiate growth are called an inoculum. The microbes that grow and multiple in or on a culture medium are known as a culture (Tortora, Funke, Case, 2010, p.164). Basically, all culture media are liquid, semi-solid, or solid. A liquid medium lacks a solidifying agent and is referred as a broth medium. A broth medium supplemented with a solidifying agent called agar results in a solid or semi-solid medium. Agar is an extract of seaweed; a complex carbohydrate composed mainly of galactose, and is without nutritional value. Agar serves as an excellent solidifying agent because it liquefies at 100oC and solidifies at 40oC. Because of these properties, microbes, especially pathogens, can be cultivated at temperatures of 37.5oC or slightly higher without fear of the medium liquefying (Cappucino &Natalie, 2011, p.1). While in the liquefied state, solid media can be placed in a test tube, which are then allowed to cool and harden in a slanted position, producing agar slant. These are useful for maintaining pure cultures. However, they may ne liquefied in a boiling water bath and poured into Petri dishes, producing Petri plate or also can be known as agar plate. This will provide larger surface areas for the isolation and study of microbes. Sterilization is the process of rendering a medium or material free of all forms of life (Cappucino &Natalie, 2011, p.2). Therefore, the medium will be initially sterile- that is, it will be initially contain no living microbes- so that the culture will contain only the microbes we added to the medium (Tortora, Funke, Case, 2010, p.165).

Microbes must be transferred from one vessel to another or from stock culture to various media for maintenance and study. Such a transfer is called subculturing and must be carried out under sterile conditions to prevent possible contamination (Cappucino &Natalie, 2011, p.3). Microbes are always present in the air and on laboratory surfaces, benches and equipment. They can serve as a source of external contamination and thus interfere with experimental results unless proper techniques are used during subculturing (Cappucino &Natalie, 2011, p.7). Aseptic technique is always used during subculturing the microbes in the...
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