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The broth microdilution method can be used to test the susceptibility of microorganisms to multiple antibiotics at once. [4] Broth microdilution is also highly accurate. The accuracy of its results are comparable to agar dilution, the gold standard of susceptibility testing. Other advantages include the commercial availability of plates, the ...
The MIC is determined by preparing a dilution series of the chemical, adding agar or broth, then inoculating with bacteria or fungi, and incubating at a suitable temperature. The value obtained is largely dependent on the susceptibility of the microorganism and the antimicrobial potency of the chemical, but other variables can affect results ...
It can be determined from broth dilution minimum inhibitory concentration (MIC) tests by subculturing to agar plates that do not contain the test agent. The MBC is identified by determining the lowest concentration of antibacterial agent that reduces the viability of the initial bacterial inoculum by ≥99.9%. [2]
Agar dilution is one of two methods (along with broth dilution) used by researchers to determine the minimum inhibitory concentration (MIC) of antibiotics. It is the dilution method most frequently used to test the effectiveness of new antibiotics when a few antibiotics are tested against a large panel of different bacteria. [1]: 149 [2]
In agar and broth dilution methods, bacteria are placed in multiple small tubes with different concentrations of antibiotics. [14] Whether a bacterium is sensitive or not is determined by visual inspection or automatic optical methods, after a period of incubation. [5] Broth dilution is considered the gold standard for phenotypic testing. [14]
Another method commonly employed to measure antimicrobial activity in liquid is to expose dilution series of the antimicrobial agent to cells in rich broth such as Mueller-Hinton broth (MHB) in a 96-well plate, and then incubate the 96-well plate at 37 °C overnight. Each well will either become turbid with bacterial growth or remain clear.
The standard can be compared visually to a suspension of bacteria in sterile saline or nutrient broth. If the bacterial suspension is too turbid, it can be diluted with more diluent. If the suspension is not turbid enough, more bacteria can be added. McFarland nephelometer standards:{2}
[1] [2] Although the disk diffusion test cannot be used to differentiate bacteriostatic and bactericidal activity, it is less cumbersome than other susceptibility test methods such as broth dilution. [4] In drug discovery labs, the disk diffusion test is performed slightly differently than in diagnostic labs.