SC246 Microbiology

General questions about the class~

Discussion Board- Participate throughout the week- Respond to at least 2 classmates posts

1. Give 3 examples of safety procedures you should always follow in the microbiology lab.

Microorganisms are normally present in the environment and many kinds are carried onand in the human body. However, the varieties and concentrations of microorganismsfound in a microbiology laboratory are such that special precautions must be taken for thesafety of the student and those around him or her.

Everyone must wear a lab coat or lab apron while in the laboratory. Do not work with an uncovered open cut. Bandages and plastic gloves are

available if needed. Upon entering the lab, and after finishing, wash down your bench space with

the disinfectant provided. Keep all sources of possible contamination out of your mouth--hands, pencils,

laboratory ware, other items. Do not smoke or eat in the laboratory. Discard contaminated equipment such as pipettes into the disinfectant

tray provided on the bench. Petri dishes, test tubes, and similar items should beplaced in the large plastic containers provided. Pipettes are disposed of tip side down.

Closed-toed shoes must be worn at all times in the laboratory. Observe aseptic technique at all times when dealing with microbial cultures.

Wash hands with soap and water or disinfectant before leaving the laboratory.

2. Why do you stain cells before observing them under the microscope? Name some common shapes and arrangements observed when viewing bacteria under a microscope.

Average size: 0.2 -1.0 µm 2 - 8 µm Basic shapes: cocci, rods, spiral

Unusual shapes Star-shaped Stella Square Haloarcula

Figure 4.5

Pairs: diplococci, diplobacilli

Clusters: staphylococci

Chains: streptococci, streptobacilli

Questions from text3. In a Gram stain,

one step could be omitted and still allow differentiation between gram positive and gram negative cells. What is that one step?

3. In a Gram stain, one step could be omitted and still allow differentiation between gram positive and gram negative cells. What is that one step?

The counterstain!

4. Assume that you are viewing a Gram-stained sample of vaginal discharge. Large (10um) nucleated red cells are coated with small (0.5 um X 1.5 um) blue cells on their surfaces. What is the most likely explanation for the red cells and blue cells?

5. A sputum sample from Calle, a 30-year-old Asian elephant, was smeared onto a slide and air dried. The smear was fixed, covered with carbolfuchin, and heated for 5 minutes. After washing with water, acid alcohol was placed on the smear for 30 seconds. Finally, the smear was stained with methylene blue for 30 seconds, washed with water, and dried. On examination at 1000X, the zoo veterinarian saw red rods on the slide. What infection to the results suggest? (Calle was treated and recovered.)

Acid fast bacteria have mycolic acid in their cell wall

Mycolic acid is a waxy material which makes acid-fast bacteria resistant to the Gram stain procedure

Acid fast bacteria include the genus Mycobacterium

members can cause TB or leprosy

Photo credit: http://commons.wikimedia.org/wiki/File:Mycobacterium_tuberculosis_Ziehl-Neelsen_stain_02.jpg

Discuss 2 other examples of staining techniques, and when they are used.

Negative staining is useful for capsules.

Heat is required to drive a stain into endospores.

Flagella staining requires a mordant to make the flagella wide enough to see.

Figure 3.13

Tortora, G., Funke, B., & Case, C. (2007). Microbiology: An Introduction (8th ed.). San Francisco, CA: Pearson.