The Composition, Uses And Preparing Of Blood Agar

Throughout the world of scientific research, there are hundreds of tests that are carried out regularly, and quite often, a hundred variation of each one of them.

The Composition, Uses And Preparing Of Blood Agar

From an outside perspective, it can be hard to distinguish what each test does from the other, especially when scientific terms are being used. After all, how likely is the everyday person supposed to know what a blood agar test is looking for from just the name?

However, the functions that these tests search for are vital to both modern research, as well as studying the ways that research is applied.

So, if you are going into a profession or role that requires this sort of thing from you, it certainly pays to know what you are studying and looking for!

This is why we have come up with this guide for you, specifically about blood agar and its research purposes.

We are going to explain what exactly this type of test is used for, what the test’s composition is, as well as the preparation that goes into using one of these tests.

There’s plenty to discuss, so let’s get started!

What Is Blood Agar?

Before we start discussing what you can use blood agar to test for, it is probably worth giving a brief introduction as to what it is in the first place, especially if you are new to scientific terms and research.

Blood agar is what is known in the field of scientific research as a basal medium. 

Basal Mediums

Basal mediums are a scientific medium, effectively a way to grow bacteria and microscopic life forms for studying under laboratory conditions, that can be used to grow cultures or colonies of bacteria without the need for giving the cultures extra enrichment to allow them to grow.

From a scientific and logistical standpoint, this means that you do not have to be concerned about continuously providing the culture of bacteria that you are growing with a steady supply of nutrients.

It isn’t ideal for every form of testing, however, as, without external factors assisting in the growth of bacteria cultures, bacteria that are tested in this sample aren’t necessarily expected to grow colonies in the same way as enriched mediums.

What Is The Composition Of Blood Agar?

As a medium that is designed to allow bacteria to grow and propagate, blood agar has to contain an appropriate amount of nutrients for it to be viable for laboratory testing.

That includes an appropriate amount of proteins, extracts, and minerals for them to survive outside their usual conditions.

In blood agar’s case, a solution of blood agar should contain:

  • 0.3% of beef or yeast extract
  • 0.5% Peptone
  • 0.5% Sodium Chloride/Salt
  • 1.5% Agar 
  • A pH of approximately 7.2 to 7.6
  • 5% Sheep Blood, although mammalian blood is the key detail.
  • Distilled water

Uses For Blood Agar

As we have established, as a basal medium, blood agar is the perfect media that can grow and sustain cultures of bacteria that a researcher or scientists may be looking to study.

In particular, blood agar is an excellent substance to measure the rate of hemolysis that a bacterium may be causing.

Hemolysis is the process of breaking down red blood cells that are happening in the body that is a normal process but can be inhibited or accelerated with the interference, infection, or presence of some pathogens, such as in Haemophilus influenza.

Many of these species are very difficult to grow and cultivate in laboratory conditions, so having a media that can allow them to propagate and grow while being observed is vital for the continued research of these bacteria.

The fact that the sample uses blood as part of its composition allows the pathogen to sustain itself on it, alongside the extra proteins and extracts that the blood agar contains.

Principles Of Using Blood Agar

When it comes to using blood agar in a research test or experiment, there are a few extra principles that should be kept in mind when using this basal medium in your studies.

As we have already mentioned, this type of medium is perfect for testing for the presence of bacteria that can inhibit or accelerate the breakdown of red blood cells.

However, different types of blood that are added to the blood agar as its base will often help support and cultivate different cultures of microorganisms.

  • For example, sheep’s blood is ideal blood to use for the cultivation of Streptococci group A types of bacteria, but cannot be used when trying to cultivate Haemophilus haemolyticus, an endocarditis-causing pathogen that is considered a clinically invasive disease. 
  • On the other hand, Haemophilus haemolyticus is best cultivated using horse blood, where it will mimic the growth patterns of Streptococci as it would normally grow in sheep’s blood.

Salt, or sodium chloride as it will often be referred to, is part of agar blood, as it helps the medium remain chemically neutral as the biological processes of the bacteria being tested are carried out in the agar.

The agar also contains a decent amount of distilled water, to make sure that the nutrients, such as the blood, proteins, and salt, are dissolved in a solution that the bacteria will be able to feed on.

Preparing Blood Agar For Testing

Preparing Blood Agar For Testing

When preparing the blood agar for a test, it is essential to follow all the given steps, to make sure that the results that you get while testing it can be validly measured.

To prepare blood agar for testing, complete the following:

  • Approximately 40 grams of this basal medium should be added to 1000 milliliters of deionized or distilled water.
  • Once the medium has been added, the suspension should then be heated up by some means, to make sure that the agar medium has dissolved into the water completely.
  • The sample should then autoclave in around 15 lbs of pressure, to make sure that the solution is properly sterilized, then kept at 121 degrees Celsius for 15 minutes.
  • After the time has passed, the medium can then be taken out from the autoclave, and be cooled to around 40 degrees Celsius, with it being no higher than 45 degrees Celsius
  • At this point, the defibrinated mammalian blood is then added to the solution and mixed.
  • The medium can then be poured into a petri dish that has been sterilized to solidify.
  • Once it has solidified, the Petri plate is then put in a hot air oven to remove any excess moisture that may be left inside.
  • When storing the Petri plate with the solution, make sure that it is kept around 20-30 degrees Celsius in a dry location, and is thoroughly dried before and after storage. 

Results Of Blood Agar Testing

There are several results that can be interpreted from a successful test of Blood Agar bacteria culture

  • If the pigment of the bacteria cultures in the medium is either gray or pigmented with round and moist edges that are smooth and glisten, then it will demonstrate that hemolysis is not taking place in the culture. The same can be said for a colorless colony with no discernible features to it, and will also be round and smooth.
  • If the sample is a golden/yellow color in the medium gel that is circular and smooth, then you will have a sample that has experienced some amount of hemolysis.

Final Thoughts

As you can see, the process through which blood agar is used and tested can be a little confusing, but the tests it carries out are vital and are pretty easy to interpret, at least when you know what you are looking for.

Jennifer Dawkins

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