Mueller Hinton Agar (MHA) is a solid medium used for the isolation and identification of bacteria.
It has been used since the 1940s and is widely used in microbiology laboratories around the world – and a basic understanding of it is crucial for your study of microbiology.
Read on to learn more about Mueller Hinton Agar, including the uses, the composition, and the best way to prepare your samples.
What Is Mueller Hinton Agar?
Mueller Hinton Agar, or MHA, is prepared from bacteriological agar and contains bacto agar, peptone, beef extract, yeast extract, glycerol, and water, and is commonly used to help differentiate between bacteria, study bacterial growth, and detect microorganisms.
They can also be used to test antimicrobial agents.
MHA is a solid medium used to isolate and identify bacteria. Bacteria are grown in liquid media such as broth or blood culture bottles and then plated onto solid media such as MHA plates.
The colonies formed on the plates are then examined under a microscope to determine their morphology and other characteristics.
The most common type of MHA is made with a specific concentration of tryptose phosphate broth and bacto agar. This form is called Trypticase Soy Broth (TSB). Other types of MHA include:
- Blood-base agar
- Chocolate agar
- MacConkey’s agar
- Mannitol salt agar
- Nutrient agar
How To Prepare Mueller Hinton Agar
Preparing for MHA is simple. You will need a sterile petri dish, an autoclave, some glassware, a mortar and pestle, and a few different ingredients. These are:
- Sterile Petri Dish
A sterile petri dish is needed to pour the MHA into. If you don’t have one, you can use any clean container that’s large enough to hold the amount of MHA you want to make.
- Autoclave
An autoclave is a pressure cooker that sterilizes items by exposing them to high heat and pressure. You’ll need a stainless steel pot and lid, which you should place inside the oven at 250 degrees Fahrenheit for 15 minutes.
Make sure there is no food or moisture inside the pot before placing it in the oven. After the time is up, allow the pot to cool down completely before opening it.
- Glassware
You’ll need a mortar and pestle for grinding the ingredients together.
To prepare MHA, you will need to add all of these components to a mortar and pestle.
- Start by adding 1 cup of distilled water to the mortar. Then add 2 tablespoons of bacto agar powder to the water.
- Next, add 1/4 teaspoon of each nutrient supplement (such as calcium chloride, magnesium sulfate, potassium dihydrogen phosphate, and sodium hydrogen carbonate), followed by 2 teaspoons of beef extract.
- Grind the mixture until smooth and mix well.
- Add another 1/4 teaspoon of bacto agar to the mixture and grind again. Repeat this process three times.
- After grinding the last batch of bacto agar, transfer the mixture to a clean jar. Add enough distilled water to fill the jar to within 1 inch of its top. Seal the jar tightly using a rubber band. Place the jar in a warm location overnight so that the mixture can ferment.
- After fermentation has occurred, remove the jar from the warm area and let it sit out for 3 hours. Pour the contents into a clean bowl. Mix the contents thoroughly. Transfer the mixture to a clean petri dish. Let the mixture set for 30 minutes.
- Pour the mixture into your desired sized Petri dishes. Allow the mixture to dry for 24 hours at room temperature. Store the MHA in a cool, dark place.
What Can I Use Mueller Hinton Agar For?
Mueller Hinton Agar has a number of potential uses, and some of the most common include:
Testing for Bacteria
One of the major uses of Mueller Hinton agar is to test for the presence of bacteria that can potentially be harmful to humans, and this is a key element of the substance. Bacteria that can be detected include:
- Staphylococcus Aureus – Staphylococcal infection can cause skin abscesses, which can lead to sepsis and even death if not treated quickly.
- Streptococcus Pneumoniae – Streptococcal pneumonia can cause severe respiratory disease.
- Escherichia Coli – E. coli is responsible for causing diarrhea, urinary tract infections, and other gastrointestinal disorders.
- Salmonella – Salmonellosis is one of the leading causes of food poisoning worldwide, and so being able to detect the pathogen quickly and easily is extremely important.
- Shigella – Shigellosis is caused by the bacterium Shigella dysenteriae, which produces bloody diarrhea and can cause serious dehydration if left untreated.
Isolating and Identifying Bacteria
In addition to testing for the presence of bacteria, Mueller Hinton Agar can be used to isolate and identify different bacteria, and this can be useful in helping scientists to determine whether a particular pathogen or bacteria is present in a sample – the different bacteria present can be isolated and dismissed or used as required, depending on the needs and nuances of the study involved.
Determining Antibiotic Sensitivity
If you suspect that a patient may be infected with a certain bacterium, you can test their susceptibility to antibiotics – once again, the ability to isolate different bacteria is very important here.
You can do this by growing the relevant bacteria on Mueller-Hinton agar plates, then applying various concentrations of antibiotics to the plate.
The highest concentration of antibiotic that kills the bacteria is called the MIC. This MIC value tells you how susceptible the bacteria is to the antibiotic, and this helps to inform research.
Identifying Yeast
Mueller-Hinton agars can also be used to identify yeast infections.
To achieve this, simply spread a small sample of an infected area onto a Mueller-Hinton agar plate, and leave the plate undisturbed for several days. Once the yeast colonies have grown, they are ready to be identified.
Are There Any Limits To Mueller Hinton Agar?
There are a few factors that can affect the results when using this agar, and these include :
Temperature
The optimal growth temperature for many bacteria is between 37 degrees Celsius and 41 degrees Celsius.
However, there are some species of bacteria that require temperatures as low as 25 degrees Celsius or as high as 45 degrees Celsius.
Therefore, you should always check the manufacturer’s instructions before using Mueller Hinton Agar.
Time
The time required for bacterial growth varies greatly depending on the type of bacteria being tested. Some types of bacteria take only a few hours to grow while others need up to 48 hours.
Therefore, you will need to follow the manufacturer’s guidelines carefully if you want accurate results.
Food Available
Bacterial growth depends on the amount of food available to them. If you don’t provide sufficient nutrients, the bacteria won’t grow well.
Therefore, you should make sure that you give the bacteria enough food to grow properly.
Final Thoughts
Mueller Hinton Agar is a key component in the identification and isolation of a number of bacteria, and a must-have for any serious scientist keen to improve their results and skills in the world of microbiology.
Ever since I was a little girl, I have been fascinated by science. Every holiday I would ask for the newest science kit, and spend weeks learning with it.
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