Course Hero Logo

Incubate the nutrient agar slant at 37 c for 2448

Course Hero uses AI to attempt to automatically extract content from documents to surface to you and others so you can study better, e.g., in search results, to enrich docs, and more. This preview shows page 14 - 19 out of 50 pages.

9.Incubate the nutrient agar slant at 37° C for 24–48 hours.2.CULTURE TECHNIQUEWhen we try to study the bacterial flora of the body, soil, water, food, or any other part of ourenvironment, we soon discover that bacteria exist in mixed populations. It is only in very raresituations that they occur as a single species. To be able to study the cultural, morphological,and physiological characteristics of an individual species, it is essential, first of all, that theorganism be separated from the other species that are normally found in its habitat; in otherwords, we must have a pure culture of the microorganism. Several different methods ofgetting a pure culture from a mixed culture are available to us. The two most frequently usedmethods involve making a streak plate or a pour plate. Both plate techniques involve thinningthe organisms so that the individual species can be selected from the others.STREAK PLATE METHODFor economy of materials and time, this method is best. It requires a certain amount of skill,however, which is forthcoming with experience. A properly executed streak plate will give asgood isolation as is desired for most work. Figure 2.6 illustrates how colonies of a mixedculture should be spread out on a properly made streak plate. The important thing is toproduce good spacing between colonies.Figure 2.6: If your streak reveals well-isolated colonies of three colors (red, white and yellow), you willhave a plate suitable for subculturing.Materials:Wire loop, china marking pencil1 nutrient agar sterile Petri plate1 mixed culture ofStaphylococcus epidermidis,Escherichia coli,andStreptococcusviridans.
151.Prepare your tabletop by disinfecting its surface with the disinfectant that is availablein the laboratory. Use a sponge or cotton to scrub it clean.2.Label the bottom surface of an agar sterile Petri plate with your name and date. Use achina marking pencil.3.Streak the plate by one of the methods shown in figure 2.8. Your instructor willindicate which technique you should use.Caution:Be sure to follow the routine in figure 2.7 for getting the organism out ofculture.4.Incubate the plate in an inverted position at 25° C for 24–48 hours. By incubatingplates upside down, the problem of moisture on the cover is minimized.
16Figure 2.7. Routine for inoculating a petri plate.Figure 2.8. Four different streak techniques.
17Figure 2.93.SUBCULTUREThe next step in the development of a pure culture is to transfer the organisms from the Petriplate to a tube of nutrient broth or a slant of nutrient agar. After this subculture has beenincubated for 24 hours, a stained slide of the culture can be made to determine if a pureculture has been achieved. When transferring the organisms from the plate, an inoculatingneedle (straight wire) is used instead of the wire loop. The needle is inserted into the center ofthe colony where there is a greater probability of getting only one species of organism. We dosubculture by the technique in the figure 2.4.
18

Upload your study docs or become a

Course Hero member to access this document

Upload your study docs or become a

Course Hero member to access this document

End of preview. Want to read all 50 pages?

Upload your study docs or become a

Course Hero member to access this document

Term
Fall
Professor
N/A
Tags
Microbiology, Bacteria, Agar plate, Petri dish, inoculating loop, nutrient agar

Newly uploaded documents

Show More

Newly uploaded documents

Show More

  • Left Quote Icon

    Student Picture

  • Left Quote Icon

    Student Picture

  • Left Quote Icon

    Student Picture