Bacteriology Lab Techniques

Flashcards covering aseptic technique, different staining methods (simple, negative, differential, Gram), bacterial morphology, and specialized structures like endospores and capsules from the lecture notes.

Aseptic Technique

The process of growing pure (uncontaminated) cultures, essential for proper characterization of bacteria, involving sterile media and equipment, and proper handling procedures to prevent contamination.

Pure Culture

A culture containing only one type of organism, necessary for identifying a single member of a group or determining the cause of a disease.

Streak-Plate Method

The standard method of obtaining a pure culture on agar, which is an example of a solid dilution technique.

Bacterial Staining

Techniques that use chemical compounds (stains) to increase the contrast between bacterial cells and the background, making them visible under a bright-field microscope.

Basic (Positively Charged) Dyes

Stains that are attracted to negatively charged cell components, coloring the bacterial cell itself.

Acid (Negatively Charged) Stains

Stains that are attracted to the glass slide surface, leaving the bacteria unstained in a stained background.

Fixing

The process of immobilizing cells to a surface (commonly a glass slide) before applying dye, usually killing the cell.

Simple Stains

Staining techniques that use a single basic dye to increase contrast between the cell and the background, staining all cells the same color.

Negative Stains

Staining techniques that use acidic dyes to color only the background, leaving the cell unstained.

Differential Stains

Staining techniques that use a combination of dyes to distinguish between cells with different chemical properties.

Gram Stain

The most widely used complex and differential staining procedure in bacteriology, which differentiates bacteria based on their cell wall's peptidoglycan content.

Gram-Positive Bacteria

Bacteria with cell walls containing thick layers of peptidoglycan (90% of cell wall), which stain purple in a Gram stain.

Gram-Negative Bacteria

Bacteria with cell walls containing thin layers of peptidoglycan (10% of cell wall) and high lipid content, which stain pink in a Gram stain.

Crystal Violet

The primary stain used in the Gram staining procedure, applied to a heat-fixed smear.

Gram's Iodine

A mordant used in the Gram staining procedure that binds to crystal violet, forming a complex within the cell.

Safranin

The counterstain used in the Gram staining procedure, which stains decolorized Gram-negative cells pink.

Cocci

Round-shaped bacterial cells.

Bacilli

Rod-shaped bacterial cells.

Spirilla

Spiral-shaped bacterial cells.

Endospores

Highly resistant 'resting bodies' formed by certain bacteria (e.g., Bacillus, Clostridium) when essential nutrients or water are unavailable, impermeable to most stains without heat.

Capsules and Slime Layers

Structures composed of polysaccharide or polypeptide layers covering the cell surface; a capsule is distinct and round/oval, while a slime layer is irregularly shaped and loosely bound, offering protection from phagocytosis.

Methylene Blue

A basic dye used as a simple stain that colors negatively charged cell structures blue.

Nigrosin

An acidic dye used in negative staining which colors the background and not the cell.