Culture Media Classification

A microbiologist is working with a bacterial sample that contains multiple species. Which term best describes this type of culture?

A researcher needs to grow a fastidious respiratory bacterium. Which type of agar would be most suitable for this purpose?

In a clinical lab, which type of media is used to differentiate bacteria based on their ability to lyse red blood cells?

A microbiologist is preparing a medium where the exact chemical composition must be known. Which type of medium should they use?

Which type of media is designed to inhibit the growth of gram-negative bacteria while promoting the growth of gram-positive bacteria?

A microbiology lab uses a medium that solidifies at room temperature but liquefies when heated to the boiling temperature of water. How would you classify this media based on its physical state?

A researcher aims to isolate Neisseria species from a clinical sample. Which selective medium should they use?

Liquid Media (Broth)

A pure culture has one type of organism.
A mixed culture has two or more species.

Culture Media Classification

Culture media can be classified based on physical state, chemical composition, and functional type.

Physical State

Liquid media (broth) are water-based solutions.
Semisolid media clots at room temperature.
Solid media is solid at room temperature but becomes liquid at boiling temperature of water.

Chemical Composition

Chemically defined (synthetic) media contains pure compounds with a chemical content specified by an exact formula.
Complex media (nonsynthetic) has one or more components not chemically defined and cannot be represented by an exact chemical formula.

Functional Types of Media

General-purpose media are for microbes that do not have special growth requirements.
Nutrient agar and Trypticase soy agar (TSA) are examples of general purpose media.
Enriched media contain complex organic substances, such as blood.
Blood agar detects the ability to produce hemolysins.
Chocolate agar is for respiratory bacteria.
Thayer-Martin agar is for Neisseria.
Selective media contain one or more agents that inhibit the growth of a certain microbe, favoring or selecting a certain microbe and allowing it to grow.
Phenylethyl alcohol agar is selective for gram-positive bacteria and inhibits the growth of gram-negative bacteria.

Different types of culture media are classified based on their physical state, chemical composition, and functional type. Physical states include liquid, semisolid, and solid media. Chemical compositions can be chemically defined or complex, depending on the specificity of their formulas.