Portage Microbiology Lab Exam 3
Study online at https://quizlet.com/_a16v4r
1. 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
2. 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.
3. You wish to study the motility of a particular bacterium. What type of mount-
ing 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).
4. What dye do Gram-positive bacteria primarily retain?: crystal violet
5. 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.
6. Identify the Gram status (positive or negative) and shape of the bacteria
pictured below.: Gram-negative; Bacillus (rod)
7. 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.
8. Why do bacteria repel the dye nigrosin?: Nigrosin is a negatively charged dye. The membranes
of most cells are also negatively charged. The membrane will repel the dye not allowing it to be absorbed.
9. What is one disadvantage of heat fixing a sample?: The heat fixing procedure kills the
specimen. This also prevents any observations on motility and enzymatic properties.
10. What is the proper way to dispose of all materials used during the lab?: All
materials must be place in a biohazardous waste bag and placed into an autoclave for sterilization.
11. What are the Gram status, shape and identification of organism #2 from
the Gram stain procedure?: Gram-negative; Bacillus (rod); E. Coli
12. What are the Gram status, shape, and identification of organism #5 from
the Gram stain procedure?: Gram-positive; Cocci (spherical) chain; Streptococcus
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Study online at https://quizlet.com/_a16v4r
1. 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
2. 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.
3. You wish to study the motility of a particular bacterium. What type of mount-
ing 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).
4. What dye do Gram-positive bacteria primarily retain?: crystal violet
5. 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.
6. Identify the Gram status (positive or negative) and shape of the bacteria
pictured below.: Gram-negative; Bacillus (rod)
7. 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.
8. Why do bacteria repel the dye nigrosin?: Nigrosin is a negatively charged dye. The membranes
of most cells are also negatively charged. The membrane will repel the dye not allowing it to be absorbed.
9. What is one disadvantage of heat fixing a sample?: The heat fixing procedure kills the
specimen. This also prevents any observations on motility and enzymatic properties.
10. What is the proper way to dispose of all materials used during the lab?: All
materials must be place in a biohazardous waste bag and placed into an autoclave for sterilization.
11. What are the Gram status, shape and identification of organism #2 from
the Gram stain procedure?: Gram-negative; Bacillus (rod); E. Coli
12. What are the Gram status, shape, and identification of organism #5 from
the Gram stain procedure?: Gram-positive; Cocci (spherical) chain; Streptococcus
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