Microbiology Lab Exercises 5, 6, and 7: Smear Preparation, Simple Staining, and Negative Staining

Vocabulary practice flashcards generated from lecture notes covering bacterial smear preparation, simple staining, negative staining, differential staining, and diagnostic applications.

Bacterial Smear

A thin lawn of bacteria fixed in place on a support, such as a glass slide, prior to staining.

Aseptic Transfer

The step in smear preparation that transfers cells to a slide while preventing contamination of the culture, environment, and laboratory personnel.

Air-drying

Allowing a bacterial smear slide to stand until all liquid evaporates in order to minimize cellular distortions after heat-fixing.

Heat-fixing

Quickly passing a slide through a Bunsen burner flame three times to adhere cells to the slide, kill them, preserve cell shape, and make them more receptive to staining.

Methanol Fixation

An alternative to heat fixation of smears before staining that results in less distortion of cell morphology and a more accurate staining result.

Chromophore

A colored particle or ion within a stain that provides essential contrast for light microscopy.

Simple Staining

A staining method that uses a single basic (cationic) dye to color all cells identically, used for quick assessment of bacterial shape, size, and arrangement.

Negative Staining

A staining method that uses a single acidic (anionic) stain, leaving cells clear while coloring the background without heat-fixing.

Differential Staining

A staining procedure that uses two or more stains for differentiating between bacterial groups or visualizing bacterial structures.

Basic Stains

Cationic dyes with positively charged chromophores that are attracted to and stick to negatively charged bacterial cell walls.

Acidic Stains

Anionic dyes with negatively charged chromophores that are repelled by negatively charged bacterial cell walls, staining the background of the slide.

Gram Stain

A differential stain used to differentiate Gram-negative from Gram-positive bacteria.

Acid-fast Stain

A differential stain used to differentiate acid-fast bacteria, such as Mycobacterium sp., from non-acid-fast bacteria.

Spore Stains

Differential staining methods, such as the Schaffer-Fulton and Domer methods, used to visualize endospores and free spores.

Simple Stain - Staphylococcus aureus

Microscopic view at 1000X magnification showing simple-stained cells of Staphylococcus aureus.

Simple Stain - Escherichia coli

Microscopic view at 1000X magnification showing simple-stained cells of Escherichia coli.

Negative Stain - Bacillus megaterium

Microscopic view at 1000X magnification showing Bacillus megaterium negatively stained with nigrosin.

Lumbar Puncture

A clinical procedure performed in a lying or sitting position to harvest cerebrospinal fluid (CSF) for diagnostic analysis.