Topics: Bacteria, Growth medium, Microbiology Pages: 3 (642 words) Published: August 4, 2014

What is the purpose of general growth media, selective media, and differential media? Give examples of each.

General Purpose Media
General Purpose media is designed to grow most organisms and do not contain growth inhibitors. Standard Methods Agar and Blood Agar Bases are examples of general purpose media. Differential Media

Differential media contain a component that allow an observable change when a specific chemical reaction takes place. Simmons Citrate Agar is an example of a differential medium. In Simmons Citrate Agar, there is a pH indicator that turns from green to blue when citrate is utilized as the sole carbon source. Selective Media

Selective media encourage the growth of some organisms and suppress the growth of others. Dyes, antimicrobials, and salts are all examples of selective agents used for this purpose. Bile Salts are used to inhibit the growth of Gram-positive organisms on MacConkey Agar.

What is a pure culture?
A culture in which only one strain or clone is present. It is usually derived from a mixed culture.

How do you obtain a pure culture?
Streak plates allow us to isolate a particular microbe from a mixed culture. Another method of obtaining a pure culture is the pour plate method. 

Name and describe the stages of bacterial growth.

1. During lag phase, bacteria adapt themselves to growth conditions. It is the period where the individual bacteria are maturing and not yet able to divide. During the lag phase of the bacterial growth cycle, synthesis of RNA, enzymes and other molecules occurs. 2. The log phase (sometimes called the logarithmic phase or the exponential phase) is a period characterized by cell doubling. 3. The stationary phase is often due to a growth-limiting factor such as the depletion of an essential nutrient, and/or the formation of an inhibitory product such as an organic acid. 4. At death phase,(Decline phase) bacteria die. This could be due to lack of nutrients, a...
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