Portage Microbiology Lab Exam 3 Latest 2022

List the four main steps used to prepare a DRY mount, and indicate which step is optional. 1 - Clean slide2 - Circle area on slide for specimen placement (OPTIONAL)3 - Apply organism to slide4 - Air dry at room temperature Why is it important to first clean your slide before applying your sample? You must first remove any unwanted contaminants from the slide otherwise it may be difficult to distinguish between the pathogen of interest and a contaminant. You wish to study the motility of a particular bacterium. What type of mounting technique would you use? Explain your answer. A wet mount technique is the best technique to use when studying motility of an organism because the sample remains viable (heat fixing kills the sample). What dye do Gram-positive bacteria primarily retain? crystal violet Why are Gram-positive bacteria able to retain the crystal violet dye? They contain a thick peptidoglycan layer in their cell wall that readily retains the dye. Identify the Gram status (positive or negative) and shape of the bacteria pictured below. Gram- negative; Bacillus (rod) When might you want to utilize a negative stain technique in the lab? What is the name of the primary dye used in this technique? A negative stain is used to identify organisms with an opaque structure. Nigrosin dye.