Lab #1

Exam 1 study guide

What is TSA/TSB?

TSA is solid agar, TSB is liquid broth

What are culture media?

solid, liquid, or semi-solid mixtures of nutrients and other substances used to support the growth, survival, and study of microorganisms in a laboratory

What is agar and what is it used for?

a gelatinous polysaccharide derived from the cell walls of red algae and growing visible colonies to identify bacteria

What is a bacterial colony?

A bacterial colony is a visible cluster of bacteria growing on the surface of a solid medium

How do bacteria start?

They start from a small clump of cells deposited onto the agar. As the cell absorbs nutrients, it divides repeatedly by binary fission, stacking up in one fixed spot

Does a single colony represent multiple species or just one?

A single well-isolated colony represents just one species

Does a single colony represent multiple individuals or just one?

A single colony represents multiple individuals (millions of individual bacterial cells) that grew from one original individual cell.

How can you tell if there’s growth in broth medium?

turbitiy, pelicle, sediment, or flocculence

What is the purpose of streak plating?

Do get individual colonies

Aseptic technique…

refers to a set of specific laboratory and medical practices used to prevent contamination by unwanted microorganisms like bacteria, fungi, and viruses

Ocular Lens (Eyepiece)

At the very top of the microscope where you look through.Magnifies the image a second time (typically by 10x).

Objective Lenses

Attached to the rotating nosepiece just above the stage.Primary lenses that gather light and magnify the specimen at varying powers.

Stage & Stage Clips

The flat, black platform below the lenses. Clips sit on top.The stage holds the slide; clips lock the slide securely in place.

Mechanical Stage Knobs

Hanging down below or to the side of the stage.Moves the slide smoothly left/right and forward/backward

Condenser

A lens assembly located directly under the hole in the stage.Concentrates and focuses light from the lamp onto the sp

Iris Diaphragm

Built into the condenser unit beneath the stage.Controls the amount of light reaching the slide by opening or closing a shutter

Coarse Adjustment Knob

The larger, outer dial on the lower side of the microscope.Moves the stage rapidly up and down for initial focusing (never use under high power or oil)

Fine Adjustment Knob

The smaller dial, often centered inside or next to the coarse knob.Moves the stage precisely to bring the image into sharp, crisp focus.

Light Source (Illuminator)

Built directly into the base at the bottom.Provides steady light that shines upward through the specimen.

Why is oil used for immersion lens?

to prevent light from bending

Basic Dye

Has a positively charged chromophore (color ion). Because bacterial cell walls have a net negative charge, the positive dye binds directly to the cell. It is used for direct staining to color the actual bacterial cells (e.g., Crystal Violet, Methylene Blue, Safranin)

Acidic Dye

Has a negatively charged chromophore. Because it is repelled by the negative bacterial cell wall, the dye stains the background instead of the cells. It is used for negative staining to view delicate structures like capsules or cells that cannot tolerate heat-fixing (e.g., Nigrosin, India Ink).

What are the shared steps of differential stains?

1. primary

2. mordant - intensifies stain

3. decolonizer

4. counterstain

Acid-fast staining is…

a differential staining technique used to distinguish bacteria that possess a thick, waxy layer of mycolic acid in their cell walls from those that do not

acid fast positive

red

acid fast negative

blue

Tuberculosis (TB)

Caused by Mycobacterium tuberculosis

Leprosy (Hansen's Disease)

Caused by Mycobacterium leprae.

Nocardiosis

A severe lung and skin disease caused by Nocardia species.

how do negative stains differ?

no heat fixing, no cell distortion, and chemistry repels the dye away from species

What is negative stains used for?

fragile organisms, accurate size measurements, and capsule detection

What dye does negative stains use?

acidic dye like Nigrosin that is negatively charged

How do you perform a negative stain?

1. drop

2. inoculate

3. spread

4. air dry

What is true motility?

Directed, purposeful movement where an individual organism can swim independelty over a significant distance like EVAPORATION

What is non-motility?

Bacteria is trapped in a fixed area, shaking or drifting without an independent navigation like Brownian motion