One might ask why agar, as opposed to regular gelatin like that found in Jello , is used for culturing bacteria. The answer is agar, unlike gelatin, won't be degraded eaten by bacteria. Also, agar is firmer and stronger than gelatin. It's still possible, however, to use gelatin as a culture medium for bacteria if agar is unavailable.
For students growing bacteria at home without the supervision of a teacher for example, investigating bacteria growth at various places around the house , it's important to use an agar formulation that does not preferentially grow one kind of bacteria over another. The worst case would be one that preferentially grew pathogenic bacteria. Therefore, we recommend a plain nutrient agar.
Ready-to-use petri dishes with nutrient agar can be purchased directly from Carolina Biological. Different types of agar are used for growing different strains of bacteria. Generally, an experimental procedure will tell you what type of agar to use. If you are still unsure, ask a teacher or consult our Ask An Expert forum. Not all types of agar are good for students to use unsupervised at home.
The following list will give you an overview of a few of the types of agar commonly found in laboratories. Many of these can be bought from Carolina Biological. Blood Agar Contains blood cells from an animal e. No, due to potential for contamination from human contact. 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. 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. MacConkey Agar This is an agar upon which only Gram-negative bacteria can grow.
What is more is that E. 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. If you get red colonies, you know the E.
No, due to selectivity. Yes, but sticking with the generic formula is recommended. Neomycin Agar Contains the antibiotic neomycin, which found in many medications such as creams, ointments and eyedrops.
Neomycin was discovered in 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.
No, due to safety concerns. Mannitol salt agar MSA selects for organisms that ferment mannitol by turning the plate yellow through a pH change. MSA also differentiates between the pathogenic and non pathogenic type of Staphylococci. Sabouraud dextrose agar SDA allows growth of fungi, yeasts and mold and has a low pH, preventing growth of bacteria. Sarah Quinlan has experience writing for various websites on science, biology, veterinary science, health and medicine.
For over seven years she has worked as a scientist in various biological fields where she has written and contributed to multiple manuscripts that have been published in scientific journals.
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