Culture (World of Microbiology and Immunology)
A culture is a single species of microorganism that is isolated and grown under controlled conditions. The German bacteriologist Robert Koch first developed culturing techniques in the late 1870s. Following Koch's initial discovery, medical scientists quickly sought to identify other pathogens. Today bacteria cultures are used as basic tools in microbiology and medicine.
The ability to separate bacteria is important because microorganisms exist as mixed populations. In order to study individual species, it is necessary to first isolate them. This isolation can be accomplished by introducing individual bacterial cells onto a culture medium containing the necessary
To grow the culture, a number of the cells of the microorganism must be introduced to the sterilized media. This process is known as inoculation and is typically done by exposing an inoculating loop to the desired strain and then placing the loop in contact with the sterilized surface. A few of the cells will be transferred to the growth media and under the proper conditions, that species will begin to grow and form a pure colony. Cells in the colony can reproduce as often as every 20 minutes and under the ideal conditions, this rate of cell division could result in the production of 500,000 new cells after six hours. Such rapid growth rates help to explain the rapid development of disease, food spoilage, decay, and the speed at which certain chemical processes used in industry take place. Once the culture has been grown, a variety of observation methods can be used to record the strain's characteristics and chart its growth.
See also Agar and agarose; Agar diffusion; American type culture collection; Antibiotic resistance, tests for; Bacterial growth and division; Bacterial kingdoms; Epidemiology, tracking diseases with technology; Laboratory techniques in microbiology
Culture (World of Forensic Science)
One aspect of the forensic examination of samples or of a crime or accident scene can involve determining whether or not a particular microorganism is present. Disease-causing (pathogenic) micro-organisms including bacteria and viruses are capable of causing illness and death, or may have contaminated a food or water source.
Modern techniques exist that rely on the detection of the genetic material of the microorganism and do not require the growth of the organism. Indeed, the organism can be dead and still remain detectable. However, the more traditional growth-dependent identification techniques are reliable, inexpensive, and are still widely used.
Bacteria require a food source to grow. Depending on the type of bacteria, the liquid or solid food source (growth medium) can be very general or highly specific, requiring the presence of certain types of amino acids, carbon sources, and other compounds. As well, some bacteria require the presence of oxygen (aerobic bacteria), while others require the complete absence of oxygen (anaerobic bacteria).
When the bacteria-containing sample is added to the medium in the step called inoculation, living bacteria will begin to assimilate the nutrients and use them to repair damaged components and construct new components. As a result, the bacteria will begin to grow and divide to produce two progeny bacteria.
Over the course of hours, the cycle of growth and division is repeated thousands of times. With each round of division, cell numbers double (i.e., growth is exponential). This rate of growth quickly leads to huge numbers of bacteria in the liquid medium or on the solid medium. This causes the liquid to become cloudy. On the surface, the countless growth and division cycles lead to the formation of a visible mound of bacteria that is known as a colony.
Bacteria can be cultured in different types of media and the various resulting biochemical reactions can be used to identify the type of organism that is present. Differing appearance of the colonies on the solid medium or the production of various compounds in the presence of specific nutrients can all be clues to the identity of the microoganism. Depending on the type of bacterium, culture-based identification can take from several days to weeks.
Viruses can also be cultured and identified (typically by their shape). However, since viruses cannot grow independently, they require the presence of a host cell. For example, poliovirus is cultured using cells found in eggs. Some viruses known as bacteriophages require a bacterial host.
SEE ALSO Bacterial biology; Bacteria, growth and reproduction; Biosensor technologies; Pathogens.