Question

1. What are the contents of culturing media? What are the types of culturing media?

2. Define the following terms: inoculum/sample, broth, culture, colonies, fastidious bacteria, agar, slants.

3. Name of selective, differential , selective and differential media along with the name of bacteria.

4. What happen to alpha, beta and gamma hemolysis?

Answer 1

1. Contents of culturing media include water, agar, peptone, casein hydrolysate, meat extract, yeast extract and malt extract.  

The main types of culturing mediaCultural media

• Minimal media -A defined medium that has just enough ingredients to support growth is called a Minimal Medium. The number of ingredients that must be added to a minimal medium varies enormously depending on which microorganism is being grown.
• Cultural media - Cultural media contains all the elements that most bacteria need to grow and are not selective, so they are used for general cultivation and maintenance of bacteria kept in collections of laboratory culture
• Selective media- Selective media are only used to cultivate chosen micro-organisms. For example, if a microorganism is resistant to some antibiotic, such as ampicillin or tetracycline, then that antibiotic may be added to the medium to prevent the growth of other cells that do not have the resistance.
• Differential media - Differential or indicator media distinguish one microorganism type from another growing on the same medium.This type of media uses the biochemical characteristics of a microorganism growing in the presence of specific nutrients or indicators (such as neutral red, phenol red, eosin y, or methylene blue) added to the medium to visibly indicate the defining characteristics of a microorganism
• Indicator media -Enriched media contain the nutrients required to support the growth of a wide variety of organisms, including some of the more fastidious ones.. Blood agar is an enriched medium in which nutritionally rich whole blood supplements the basic nutrients. Chocolate agar is enriched with heat-treated blood (40–45 °C), which turns brown and gives the medium the color for which it is named.

2. inoculum - A small amount of substance containing bacteria from a pure culture which is used to start a new culture or to infect an experimental animal.

broth- a liquid medium containing proteins and other nutrients for the culture of bacteria.

culture - culture, or microbial culture, is a method of multiplying microbial organisms by letting them reproduce in predetermined culture medium under controlled laboratory conditions

colony-  A colony is defined as a visible mass of microorganisms all originating from a single mother cell, therefore a colony constitutes a clone of bacteria all genetically alike

fastidious bacteria- A fastidious bacteria is any bacteria that has complex or particular nutritional requirements. In other words, a fastidious bacteria will only grow when specific nutrients are included in its medium

Agar slant -An agar slant tube (or simply an agar slant) is a screw-capped culture tube partly filled with an agar mix such as nutrient agar.

3. selective media- Eosin methylene blue contains dyes that are toxic for Gram-positive bacteria. It is the selective medium for coliforms (E.coli)

diffrential - Blood agar is a differential medium that distinguishes bacterial species by their ability to break down the red blood cells included in the media. Blood agar is often used to distinguish between the different species of pathogenic Streptococcus bacteria

4. Alpha-hemolytic Streptococcus, like those that cause pneumonia, produce a narrow band of slimy discoloration around the colony during the partial breakdown of the red blood cells.

Beta-hemolytic Streptococcus, like those that cause potentially deadly infections in newborns, produce a completely clear zone around the colony during the complete breakdown of the red blood cells.

Gamma-hemolytic Enterococcus, which used to be called Group D Streptococcus, don't change the media appearance at all since they can't break down the red blood cells.