Agars- the oldest yet the latest microbiological tool

Hi, there guys!

It’s been a long time but guess what, I’m back. Anyway, as a laboratory personnel, I believe, you are already exposed to different kinds of pathogens and the risk groups which we have discussed in the previous post. Pathogens were given the emphasis on my previous blog, so now, I would like to put the focus on Agars.
What is an Agar? Agar is a gelatinous substance obtained from various kinds of red seaweed and used in biological culture media and as a thickener in foods. Nowadays in laboratory, agar is used as a growth medium in which microorganisms including bacteria and fungi, can be cultured and observed under the microscope. 

Without agars, there will be no cultures too. They are one of the most important microbiological tools inside the laboratory, it may be for research or for clinical analysis. Agars have been widely used as microbiological mediums since 1882 by a German Microbiologist named Walter Hasse, assistant of Robert Koch up until now. Agars have contributed a lot not only in the field of microbiology but to a lot of fields in science. So today, let take a look at the different types of agars and to what pathogens they are applied to use for.
Below are the types of agars that are commonly used:

Here are the list of common types of agar with brief definition.

1. Nutrient Agar
   - Will grow the largest number of different types of microbes - fungi and bacteria. Yet, not all bacteria can grow on these. Some find it too rich, and others find it deficient. The nutrient in this is beef broth, and some extracts from yeast.Escherichia coli, Bacillus subtilis, Streptococcus faecalis, and Saccharomyces diastaticus commonly grown in this agar.
2. Blood Agar
   - Contains blood cells from an animal example sheep, most bacteria will grow on this medium.Staphylococci and Streprococci are common pathogens grown in blood agar.
3. Sabouraud Agar
   - Used for fungi and has a low pH that will kill most bacteria. It contains gentamicin, which is an aminoglycoside antibiotic. Gentamicin can also treat many different types of bacterial infections, particularly Gram-negative infection.
   Examples of pathogens used areAspergillus spp., Cryptococcus neoformans, etc.
4. Chocolate Agar
   - Comprised of sheep blood that provides the X and V factors necessary for Haemophilus growth, this is a nutrient medium which is used in culturing fastidious organisms such as Haemophilus species and Neisseria. Chocolate agar, however, does not reveal hemolysis data, so species differentiation among the members of Haemophilus must be performed in another manner.
5. MacConkey Agar
   - This is an agar upon which only Gram-negative bacteria can grow. What is more is that coli will grow into red colonies, as there is a pH indicator present. It should be mentioned that MacConkey agar powder comes in two versions: one with the sugar lactose in it, and one without any added sugars. Since E.coli ferments sugars to acids (thus the red color), one can add one of the many different kinds of sugars to this sugar-free MacConkey agar and see if red colonies develop. If you get red colonies, you know the E.coli strain you are using can use that sugar.
6. Miller's LB Agar
   - This common variation of LB agar appears to have the same components as LB, just in different proportions.
7. Thayer-Martin Agar
   - Chocolate agar designed to isolate Neisseria gonorrhoeae, also known as "gonococcus," which is a species of Gram-negative bacterium responsible for the disease gonorrhoea.
8. XLD Agar
   - Xylose lysine deoxycholate agar. It is used for the culture of stool samples, and contains two indicators. It is formulated to inhibit Gram-positive bacteria, while the growth of Gram-negative bacilli is encouraged. The colonies of lactose fermenters appear yellow.
9. Tryptic Soy Agar
   - A basic medium used for culturing many kinds of microorganisms. Tryptic soy agar is mainly used as an initial growth medium for the purposes of observing colony morphology, developing a pure culture, achieving sufficient growth for further biochemical testing, and culture storage.
10. LB (Luria Bertani) Agar
    - A subtype of nutrient agar, this is the general medium for microbiology studies and may be used for routine cultivation of not particularly fastidious microorganisms. Also, does not preferentially grow one kind of bacteria over another.
11. Neomycin Agar
    - Contains the antibiotic neomycin, which found in many medications such as creams, ointments and eye drops. Neomycin was discovered in 1949 by the microbiologist Selman Waksman, and it is produced naturally by the bacterium Streptomyces fradiae. Moreover, Neomycin has a broad spectrum of effects, killing both gram-positive and gram negative bacteria. It is relatively toxic to humans, and some people have allergic reactions to it. Often, Neomycin agar is used for culturing organisms anaerobically. Neomycin stops the growth of gram-negative bacilli and staphylcocci, allowing Streptococcus species to grow more abundantly.

There you have it guys! Please also note that incubation period varies depending on what microorganism you are working on. Don’t forget that all microorganisms grown during the experiment should be demolished before discarding. The best way to dispose bacterial cultures is to pressure sterilize them in a heat stable biohazard bag. I hope that this gave additional information that you can use when working in the laboratory!
                                    Have a great day! And best of luck on your job!

Source:  http://www.sciencebuddies.org/science-fairprojects/project_ideas/MicroBio_Agar.shtml