Microbio - Lab. 1, 2, and 3

Wet Mount Slide

A microscope slide preparation that requires a layer of liquid to completely fill the space between the slide and the coverslip, immersing the specimen and enabling the observer to clearly focus through the microscope.

Biological Stain

A substance applied to a specimen that combines with cellular components. Its purpose is to increase contrast between the organisms and the background so they are more readily seen in the light microscope.

Smear

A preparation made by spreading a small amount of specimen material (from an agar plate or broth culture) over a small portion of a slide until it is evenly distributed, creating a thin film with light visible turbidity.

Turbid Suspension

A mixture where specimen material is evenly distributed in a drop of water, resulting in a cloudy or non-transparent appearance.

Triplicate Smears

The practice of creating three identical slide preparations for every sample. This provides statistical validation and accounts for any errors during staining or viewing.

Simple Stain

A staining method where a bacterial smear is stained with a solution of a single dye that stains all the cells the same color, without differentiation of cell types or structures.

Methylene Blue

A type of basic stain used in simple staining. It is used because living bacteria are almost colorless and lack sufficient contrast with the water they are suspended in.

Basic Stain

A stain (like methylene blue) that has a positive charge, which allows it to bind strongly to negatively charged cell components such as bacterial nucleic acids and cell walls.

Blotting

The process of drying a stained slide by touching one corner to blotting paper or placing it between clean sheets of paper in a blotting pad. It is crucial not to rub the slide, as this will remove the smear.

Sediment

Material found at the bottom of a pond. Stirring it up and including a bit of it (along with plant life) in your sample jar provides a richer selection of microorganisms to view.

Coverslip

A small piece of glass placed gently over a drop of pond water on a slide. It flattens the sample and makes it easier to see the microorganisms.

Trapping Air Bubbles

A common issue when placing a coverslip. To avoid this, hold the coverslip at an angle, place one edge into the edge of the water droplet, and slowly lower the rest of the slip down.

Floating Coverslip

An indicator that there is too much water on the slide. If this happens, you should use the edge of a paper towel to gently soak up the excess water from the edge of the coverslip.

40x Power (Pond Water Viewing)

The magnification level used to spot larger, multi-cellular animals such as rotifers or water fleas (Daphnia).

100x Power (Pond Water Viewing)

The magnification level used to view larger protozoa.

Oil Immersion Objective

A microscope objective lens (typically 100X, yielding a total magnification of 1000X) that requires a drop of immersion oil between the slide and the lens to achieve optimal image resolution.

Immersion Oil

A special mineral oil placed on the microscope slide. It has the same refractive index as glass and prevents the loss of light that would occur due to refraction when light passes through air, thereby increasing the microscope's resolution.

Refraction

The scattering or bending of light that causes a loss of light when passing through air. Immersion oil prevents this loss.

Cocci

One of the three general shapes of bacteria; they are sphere-shaped.

Bacilli

One of the three general shapes of bacteria; they are rod-shaped.

Spirilla

One of the three general shapes of bacteria; they are spiral-shaped.

Sterilization

The process of eliminating or destroying all forms of microbial life, including vegetative cells and bacterial endospores. It is essential for making culture media, glassware, and instruments free from contaminating microorganisms.

Disinfection

A process that reduces or eliminates many harmful microorganisms on non-living surfaces, but does not necessarily destroy all microbial forms (particularly bacterial endospores). This is distinct from sterilization, which aims for complete elimination.

Vegetative Cells

The active, growing state of microbial life. These are destroyed during the sterilization process.

Bacterial Endospores

Highly resistant, dormant structures formed by some bacteria. They are targeted during sterilization but may survive standard disinfection.

Moist-Heat Sterilization (Autoclave)

One of the most commonly used methods of sterilization in labs. An autoclave uses saturated steam under pressure. A standard cycle is approximately 121°C at about 15 psi for 15–20 minutes.

Nutrient Agar

A type of culture media that must be sterilized after preparation to eliminate any contaminating microorganisms that might interfere with experiments.

Microorganisms

Living entities found almost everywhere in the environment (air, water, soil, surfaces, human body). Because they are easily transferred, lab experiments must be performed under conditions that minimize or eliminate unwanted ones.

Autoclaving

Is a moist-heat sterilization method that uses pressurized steam. The combination of temperature, pressure, and exposure time allows steam to penetrate materials and destroy microorganisms.

Culture Media

Provide nutrients and appropriate environmental conditions for microorganisms to grow. Nutrient agar is a general-purpose solid medium commonly used for cultivating many non-fastidious bacteria.

Aseptic Technique

Refers to practices used to prevent contamination of sterile materials, media, cultures, and laboratory surfaces.

Dry-Heat Sterilization

May be used for suitable heat-stable materials, particularly certain glassware. Dry-heat sterilization requires higher temperatures and generally longer exposure times than moist heat.