Background and Introduction

Media used to flourish bacteria in the activities must fulfill their nutritional requirements.  every living organisms have simple requirements because that the major element, Carbon, Hydrogen, Nitrogen, Oxygen, Phosphorous, and also Sulfur (acronym CHNOPS).  Other major elements include potassium, magnesium, calcium and also iron.  together a group, bacteria have a remarkably broad selection of metabolic abilities.  many bacteria are chemoheterotrophs that, favor us, make use of organic carbon as an energy and also carbon source.  However, there space a an excellent number that bacteria that room photosynthetic, obtaining power from light, and even part that use inorganic compounds, such as sulfate, nitrate, and ammonia, because that energy. 


Carbon & energy Sources Table

As displayed in the table below, all living organisms can be categorized based on the carbon and energy sources they utilize.  

Category

Energy Source

Carbon Source

Example

photoautotrophs

light

CO2

purple and green sulfur bacteria, algae, and also green plants

photoheterotrophs

light

Simple organics

purple and green non-sulfur bacteria

chemoautotrophs (chemolithoautotrophs)

inorganic chemicals

CO2

Thiobacillus (S), Nitrobacter (NO2-1), and Nitrosomonas (NH3)

chemoheterotrophs (chemoorganoheterotrophs

organic source eg:  glucose 

organic compounds

Most bacteria, every fungi, humans and also other animals.

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Background

Many different varieties of society media have been developed for a number of different purposes.  In general, media deserve to be split into two categories, defined and also undefined (complex) media.  A Defined medium is a fairly simple tool that is made up of specific chemicals at known concentrations.  An Undefined medium is created of mixtures of yeast cabinet extracts or enzymatic digests that protein; the exact amount and also kinds that nutrients present in the tool are no known.  one Undefined tool tends to assistance the growth of bacteria much better than a defined medium since it contains more preformed nutrients/growth determinants (amino acids, nucleotides, and also vitamins).  Consequently, organisms perform not need to expend an important energy and materials come synthesize the "preformed" compounds gave in the unknown medium.  

Microbiologists have likewise developed one-of-a-kind media that deserve to be used to choose for the development of particular organisms or differentiate between bacterial isolates based on physiological characteristics.  this media are described as selective or differential media.  Selective media contain at least one ingredient that inhibits the growth of unwanted organisms, but permits development of the preferred bacteria.  Therefore, these varieties of media permit for the isolation of a particular bacteria even if lock constitute a small percentage that the population in a sample.  Differential media are recipe to distinguish different microorganisms cultivation in the medium.  this media usually contain a chemical that is utilized or altered by some organisms but not through others.  by observing the figure of the tool or swarms growing on differential media one can identify different organisms exhibiting various physiological traits. 

Today you will certainly inoculate 3 different species of media through four various bacterial species.  The target of this exercise is to show the different growth features of biology on defined, unknown (rich), selective and differential media. 


Glucose salt Agar (GSA): is a simple, defined medium.  just organisms that deserve to make all your cellular materials from glucose and also inorganic salts are able to prosper on this medium.

 

 

 

 

 

Tryptic soy Agar (TSA): is a rich, undefined medium containing products of one enzymatic digest the protein and soy product.  biology that need vitamins or other growth factors are may be to grow on TSA. 

 

 

 

 

 

Eosin Methylene Blue (EMB) Agar: is a selective and also a differential medium.  The selective components are the eosin and also methylene blue dyes the inhibit the expansion of Gram-positive bacteria and permit the development of Gram-negative enteric rods.  The differential component of the medium is lactose, i m sorry is a street that part organisms have the right to ferment as an energy source.  Organisms that ferment lactose develop dark violet (sometimes shiny) colonies and also those the cannot, create white or an extremely light pink colonies. 

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Procedure: (work in pairs) Collect 1 GSA plate, 1 TSA plate, and also 1 EMB plate. Organisms the you will be functioning with: Escherichia coli (G-) Staphylococcus epidermidis (G+) Pseudomonas aeruginosa (G-) Enterobacter aerogenes (G-) 1. With a marker, divide the bottom the all three Petri plates into quadrants.  brand the plates v your name, laboratory section, and also the date.  label each quadrant with among the four organisms as shown in the diagram below. 

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2. Follow the procedure for Inoculating organisms into 4 quadrants. 3. Repeat the procedure because that all four organisms.  Streak lock in their as necessary labeled quadrants. 4. Repeat the inoculation procedure, as described in the video, for the remaining 2 plates.  5. Invert the plates and incubate them in ~ 37°C for 24-48 hours. 


Results


GSA plate results

Observer the development of every organism top top the GSA plate.

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TSA results

Observe the growth on the TSA plate. Compare development here to the on the GSA plate.


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EMB results

Remember that EMB is both selective and also differential. Observe the EMB plate because that growth and also the capability to ferment lactose


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