Mueller–Hinton Agar
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Mueller Hinton agar is a type of growth medium used in microbiology to culture bacterial isolates and test their susceptibility to antibiotics. This medium was first developed in 1941 by John Howard Mueller and Jane Hinton, who were microbiologists working at Harvard University. However, Mueller Hinton agar is made up of a couple of components, including beef extract, acid hydrolysate of casein, and starch, as well as agar to solidify the mixture. The composition of Mueller Hinton agar can vary depending on the manufacturer and the intended use, but the medium is generally nutrient-rich and free of inhibitors that could interfere with bacterial growth.                                                               Mueller Hinton agar is commonly used in the disk diffusion method, which is a simple and widely used method for testing the susceptibility of bacterial isolates to antibiotics. In this method, small disks impregnated with different antibiotics are placed on the surface of the agar, and the zone of inhibition around each disk is measured to determine the susceptibility of the bacterial isolate to that antibiotic. Mueller Hinton agar is particularly useful for testing a wide range of antibiotics, as it has a low content of calcium and magnesium ions, which can interfere with the activity of certain antibiotics. For example,  MH agar may be used in the laboratory for the rapid presumptive identification of C. albicans, as an alternative method for germ tube test (Mattie. As, 2014). The medium is also free of inhibitors that could interfere with bacterial growth, making it a reliable and consistent substrate for bacterial cultures. The composition of Mueller Hinton agar can affect the growth characteristics of bacterial isolates, as well as their response to antibiotics. For example, variations in the pH of the medium can affect the activity of certain antibiotics, and the presence of certain nutrients can promote the growth of specific bacterial species. More so, careful selection and preparation of Mueller Hinton agar is important for accurate microbiological assays. The use of Mueller Hinton agar has been critical in the development of antibiotics and in the study of antibiotic resistance. Mueller–Hinton agar is a
microbiological Microbiology () is the scientific study of microorganisms, those being of unicellular (single-celled), multicellular (consisting of complex cells), or acellular (lacking cells). Microbiology encompasses numerous sub-disciplines including virol ...
growth medium A growth medium or culture medium is a solid, liquid, or semi-solid designed to support the growth of a population of microorganisms or cells via the process of cell proliferation or small plants like the moss ''Physcomitrella patens''. Differe ...
that is commonly used for antibiotic susceptibility testing, specifically
disk diffusion test The disk diffusion test (also known as the agar diffusion test, Kirby–Bauer test, disc-diffusion antibiotic susceptibility test, disc-diffusion antibiotic sensitivity test and KB test) is a culture-based microbiology assay used in diagnost ...
s. It is also used to isolate and maintain ''
Neisseria ''Neisseria'' is a large genus of bacteria that colonize the mucous membranes of many animals. Of the 11 species that colonize humans, only two are pathogens: '' N. meningitidis'' and '' N. gonorrhoeae''. ''Neisseria'' species are Gram-negative ...
'' and ''
Moraxella ''Moraxella'' is a genus of gram-negative bacteria in the family Moraxellaceae. It is named after the Swiss ophthalmologist Victor Morax. The organisms are short rods, coccobacilli, or as in the case of '' Moraxella catarrhalis'', diplococci ...
'' species. It typically contains: *2.0 g
beef extract Meat extract is highly concentrated meat stock, usually made from beef or chicken. It is used to add meat flavor in cooking, and to make broth for soups and other liquid-based foods. Meat extract was invented by Baron Justus von Liebig, a Germa ...
*17.5 g
casein Casein ( , from Latin ''caseus'' "cheese") is a family of related phosphoproteins (CSN1S1, αS1, aS2, CSN2, β, K-casein, κ) that are commonly found in mammalian milk, comprising about 80% of the proteins in cow's milk and between 20% and 60% of ...
hydrolysate Hydrolysate refers to any product of hydrolysis. Protein hydrolysate has special application in sports medicine because its consumption allows amino acids to be absorbed by the body more rapidly than intact proteins, thus maximizing nutrient delive ...
*1.5 g
starch Starch or amylum is a polymeric carbohydrate consisting of numerous glucose units joined by glycosidic bonds. This polysaccharide is produced by most green plants for energy storage. Worldwide, it is the most common carbohydrate in human diet ...
*17.0 g
agar Agar ( or ), or agar-agar, is a jelly-like substance consisting of polysaccharides obtained from the cell walls of some species of red algae, primarily from " ogonori" and " tengusa". As found in nature, agar is a mixture of two components, t ...
*1 liter of distilled water. *pH adjusted to neutral at 25
°C The degree Celsius is the unit of temperature on the Celsius temperature scale "Celsius temperature scale, also called centigrade temperature scale, scale based on 0 ° for the melting point of water and 100 ° for the boiling point ...
. Five percent sheep's blood and
nicotinamide adenine dinucleotide Nicotinamide adenine dinucleotide (NAD) is a Cofactor (biochemistry), coenzyme central to metabolism. Found in all living cell (biology), cells, NAD is called a dinucleotide because it consists of two nucleotides joined through their phosphat ...
may also be added when susceptibility testing is done on ''
Streptococcus ''Streptococcus'' is a genus of gram-positive spherical bacteria that belongs to the family Streptococcaceae, within the order Lactobacillales (lactic acid bacteria), in the phylum Bacillota. Cell division in streptococci occurs along a sing ...
'' and ''
Campylobacter ''Campylobacter'' is a type of bacteria that can cause a diarrheal disease in people. Its name means "curved bacteria", as the germ typically appears in a comma or "s" shape. According to its scientific classification, it is a genus of gram-negat ...
'' species. It has a few properties that make it excellent for antibiotic use. First of all, it is a nonselective, nondifferential medium. This means that almost all organisms plated on it will grow. Additionally, it contains starch. Starch is known to absorb toxins released from bacteria, so that they cannot interfere with the antibiotics. Second, it is a loose agar. This allows for better
diffusion Diffusion is the net movement of anything (for example, atoms, ions, molecules, energy) generally from a region of higher concentration to a region of lower concentration. Diffusion is driven by a gradient in Gibbs free energy or chemical p ...
of the antibiotics than most other plates. A better diffusion leads to a truer zone of inhibition. Mueller–Hinton agar was co-developed by a microbiologist John Howard Mueller and a veterinary scientist Jane Hinton at
Harvard University Harvard University is a Private university, private Ivy League research university in Cambridge, Massachusetts, United States. Founded in 1636 and named for its first benefactor, the History of the Puritans in North America, Puritan clergyma ...
as a culture for
gonococcus ''Neisseria gonorrhoeae'', also known as ''gonococcus'' (singular) or ''gonococci'' (plural), is a species of Gram-negative diplococci bacteria first isolated by Albert Neisser in 1879. An obligate human pathogen, it primarily colonizes the m ...
and
meningococcus ''Neisseria meningitidis'', often referred to as the meningococcus, is a Gram-negative bacterium that can cause meningitis and other forms of meningococcal disease such as meningococcemia, a life-threatening sepsis. The bacterium is referred to a ...
. They co-published the method in 1941.


References

* * {{DEFAULTSORT:Mueller-Hinton agar Microbiological media Cell culture media