Show description

Using a marker, draw two bisecting lines on the bottom of the Petri dish to divide the plate into 4 equal parts. Label each quadrant 1 through 4, starting with the top right quadrant and labeling counter­ clockwise. Sterilizing the loop at the points indicated is to dilute the culture due to fewer organisms available to be streaked into each area, resulting in the final desired separation. b. Turn the Petri dish over and place a loopful of culture on the agar surface in quadrant 1. Using the edge of the loop and holding the loop at a shallow angle so as not to gouge the agar, quickly spread the bacteria throughout the quadrant.

In the absence of a turntable, turn the Petri dish manually and spread the culture with the sterile bent glass rod. 4. The pour-plate technique requires a serial dilution of the mixed culture by means of a loop or pipette. The diluted inoculum is then added to a molten agar medium in a Petri dish, mixed, and allowed to solidify. The serial dilution and pour­plate procedures are outlined in Experiment 18. C L I n I C A L A P P L I C AT I o n Isolation of Cultures as a Diagnostic Technique The isolation of pure cultures is the most important diagnostic tool used in a clinical or research laboratory to uncover the cause of an infection or disease.

4. The method for performing differential staining procedures, such as the Gram, acid-fast, capsule, and spore stains. Introduction Visualization of microorganisms in the living state is quite difficult, not only because they are minute, but also because they are transparent and practically colorless when suspended in an aqueous medium. To study their properties and to divide microorganisms into specific groups for diagnostic purposes, biological stains and staining procedures in conjunction with light microscopy have become major tools in microbiology.