<P> Streaking is rapid and ideally a simple process of isolation dilution . The technique is done by diluting a comparatively large concentration of bacteria to a smaller concentration . The decrease of bacteria should show that colonies are sufficiently spread apart to effect the separation of the different types of microbes . Streaking is done using a sterile tool, such as a cotton swab or commonly an inoculation loop . Aseptic techniques are used to maintain microbiological cultures and to prevent contamination of the growth medium . There are many different types of methods used to streak a plate . Picking a technique is a matter of individual preference and can also depend on how large the number of microbes the sample contains . </P> <P> The three - phase streaking pattern, known as the T - Streak, is recommended for beginners . The streaking is done using a sterile tool, such as a cotton swab or commonly an inoculation loop . The inoculation loop is first sterilized by passing it through a flame . When the loop is cool, it is dipped into an inoculum such as a broth or patient specimen containing many species of bacteria . The inoculation loop is then dragged across the surface of the agar back and forth in a zigzag motion until approximately 30% of the plate has been covered . The loop then is re-sterilized and the plate is turned 90 degrees . Starting in the previously streaked section, the loop is dragged through it two to three times continuing the zigzag pattern . The procedure is then repeated once more being cautious to not touch the previously streaked sectors . Each time the loop gathers fewer and fewer bacteria until it gathers just single bacterial cells that can grow into a colony . The plate should show the heaviest growth in the first section . The second section will have less growth and a few isolated colonies, while the final section will have the least amount of growth and many isolated colonies . </P> <P> The sample is spread across one quadrant of a petri dish containing a growth medium . Bacteria need different nutrients to grow . This includes water, a source of energy, sources of carbon, sulfur, nitrogen, phosphorus, certain minerals, and other vitamins and growth factors . A very common type of media used in microbiology labs is known as agar, a gelatinous substance derived from seaweed . The nutrient agar has a lot of ingredients with unknown amounts of nutrients in them . On one hand, this can be a very selective media to use because as mentioned bacteria are particular . If there is a certain nutrient in the media the bacteria could most certainly not grow and could die . On the other hand, this media is very complex . Complex media is important because it allows for a wide range of microbial growth . The bacteria growth can be supported by this media greatly due in part to the high amounts of nutrients . Choice of which growth medium is used depends on which microorganism is being cultured, or selected for . </P> <P> Dependent on the strain, the plate may then be incubated, usually for 24 to 36 hours, to allow the bacteria to reproduce . At the end of incubation there should be enough bacteria to form visible colonies in the areas touched by the inoculation loop . From these mixed colonies, single bacterial or fungal species can be identified based on their morphological (size / shape / colour) differences, and then sub-cultured to a new media plate to yield a pure culture for further analysis . </P>

How can contaminants be detected on a streaked plate after incubation