Skip to content
Quick Guides

Microbiology - Microscopy

Preview 4 of 12 pages

See the first 4 pages exactly as they appear in the document.

  1. Page 1
    Read page 1 as text

    Study Guide Microbiology – Microscopy 1. Staining Techniques Microorganisms are usually colorless and transparent , which makes them difficult to see under a light microscope. To make them visible and easier to study, scientists use staining techniques . Stains add color to microbial cells or their surroundings, helping us observe size, shape, and structure. 1.1 When Staining Is Not Needed In some situations, staining is unnecessary. For example: • When microorganisms are very large • When motility (movement) needs to be observed In these cases, a wet mount is prepared. A drop of the microbial sample is placed directly on a slide and observed. Another method is the hanging drop technique , where: • A drop of culture is placed on a cover slip • The cover slip is inverted over a hollow slide This method is especially useful for studying motility in living microorganisms. 1.2 Preparing a Smear for Staining Before staining, the microorganisms must be prepared properly: 1. A small amount of microbial sample is placed on a slide 2. The sample is allowed to air dry 3. The slide is heat fixed by passing it quickly through a flame

  2. Page 2
    Read page 2 as text

    Study Guide Purpose of Heat Fixing • Kills the microorganisms • Makes them stick to the slide • Helps cells absorb stains more effectively Simple Staining Techniques Simple Stain A simple stain uses a single dye to color the cells. • Common dyes: crystal violet , methylene blue • These are basic dyes (positively charged) • They are attracted to the negatively charged cytoplasm This method highlights: • Cell shape • Cell arrangement Negative Stain Negative staining uses acidic dyes , such as: • Nigrosin • Congo red These dyes are negatively charged and are repelled by the microbial cytoplasm. Instead of staining the cell, they color the background. Result: • Cells appear clear • Background appears dark This method is useful for observing: • Cell size • Cell shape • Capsules (if present)

  3. Page 3
    Read page 3 as text

    Study Guide 1.3 Differential Staining Techniques Differential stains use more than one dye to distinguish between different types of microorganisms. Gram Stain Technique The Gram stain is the most important differential stain in microbiology. It divides bacteria into two major groups: • Gram - positive • Gram - negative Steps in the Gram Stain 1. Crystal violet (primary stain) 2. Iodine (mordant) 3. Alcohol wash (decolorization) 4. Safranin (counterstain)

  4. Page 4
    Read page 4 as text

    Study Guide The Gram stain procedure used for differentiating bacteria into two groups . Results • Gram - positive bacteria o Retain crystal violet - iodine complex o Appear purple or blue • Gram - negative bacteria o Lose crystal violet during alcohol wash o Take up safranin o Appear red or pink Observation is done under the oil - immersion lens .

8 more pages in the full document

Unlock it once and it stays in your library, ready to chat with or turn into flashcards.

Unlock the full document

More Microbiology study materials

See all

Study this document with CramX

Once it is in your library, every tool can work from it.