Streak Plate Isolation for Obtaining Pure Cultures Data Interpretation 1- In order to unsure that you get a pure sample. 2-pure culture: laboratory culture containing a single species of organism. A pure culture is usually derived from a mixed culture (containing many species) by methods that separate the individual cells so that, when they multiply, each will form an individually distinct colony, which may then be used to establish new cultures with the assurance that only one type of organism will be present.
Pure cultures may be more easily isolated if the growth medium of the original mixed culture favors the growth of one organism to the exclusion of others. In mixed culture two or more microbial species formed colonies. 3-A bacterial colony is defined as a visible cluster of organisms growing on the surface of or within a solid medium, theoretically cultured from a single cell. Because all organisms within the colony descend from a single ancestor, they are genetically identical (except for mutations which occur at a low, unavoidable frequency, as well as the more likely possibility of contamination).
Obtaining such genetically identical organisms (or pure strains) can be useful in many cases; this is done by spreading bacteria on a culture plate and starting a new stock of bacteria from a single colony. Fours characteristics by which colonies can be identified are shape, color, size and texture. 4-A Petri dish is used as a container for a medium used to grow cultures. Leaving the Petri dish open will increase the probability that your culture will be contaminated. 5- Between each set of streaks you sterilize the inoculating loop in the Bunsen flame.
At the beginning of the next streak you overlap with the end of the one before. The effect of the technique is to “dilute” the bacteria by gradually spreading then over greater distances. Eventually, a point is reached where single bacteria are spaced sufficiently far apart for single colonies to grow without infringing their neighbors. 6- The isolation of independent bacterial species from various environmental sources is important in all branches of microbiology since bacteria are ubiquitous and live in microbial communities of mixed populations.
Populations in microbial communities or ecosystems may interact and cooperate in their efforts to obtain nutrients from the environment with the waste products from one group of microorganisms serving as nutrients for another. Alternatively, the metabolic wastes from fermentation processes of some bacteria in a population (for example acid production) may provide a favorable ecological niche for bacteria that prefer to grow at low pH. – Some organisms have complex nutritional requirements that are not easily mimicked with nutrient agar. Using blood agar will allow them to grow better. Blood agar as a media can fulfil all the requirement of most bacteria. 8-Suppose there are no deep cuts inside the mouth leading to the stomach, we will digest almost any bacteria or microbe that enters into the stomach (pH 2) when we swallow or eat.
We won’t get rid of the microbes so it is the body’s defense system to digest harmful bacteria. Basically you can assume that every portion of your body that is sufficiently wet (yes, including the stomach) harbors bacteria. If they are not pathogens it is generally a good thing as they limit the resources for pathogens by merely being (and living) there. 9-Mainly through the food we eat. It is covered with bacteria. Also by putting things in your mouth (fingers, pencils, toothpicks, etc).
