3.9

simple staining

• Wet mount uses a drop of liquid specimen overlaid with coverslip

• Allows observation of living organisms

• difficult to see - colorless

smear

drying and fixing specimen before staining to visualize

basic dyes

• carry positive charge (methylene blue & crystal violet used in gram staining)

• attracted to negatively charged cell wall

Acidic Dyes

carry negative charge and stain the background in wet mounts, creating contrast that makes cell features easier to see

Differential staining

used to distinguish different groups of bacteria

Acid-fast stain

used to detect organisms that do not readily take up dyes due to waxy outer cell wall

Capsular Stains

• Allows observation of gel-like layer that surrounds some microbes

• Capsules stain poorly, so background is stained to make capsule visible

Endospore Stains

• Allows visualization of endospores, resistant dormant cells often formed by Bacillus and Clostridium

• Uses malachite green

Flagella stains

• Can help with identification of causative agent of disease

Fluorescent stains

Allows you to view a specific subset of cells with specific characteristic of interest