The disk-diffusion agar method tests the effectiveness of antibiotics on a specific microorganism. An agar plate is first spread with bacteria, then paper disks of antibiotics are added. The amount of space around every antibiotic plate indicates the lethality of that antibiotic on the bacteria in question.

What are the limitations of the disk diffusion assay?

There are serious limitations to the use of disk diffusion method. Results may be unexpected or borderline. In such cases another method of testing may be required or the test may need to be repeated for confirmation.

What is broth dilution method?

Broth dilution is a technique in which containers holding identical volumes of broth with antimicrobial solution in incrementally (usually geometrically) increasing concentrations are inoculated with a known number of bacteria.

What is Stoke method?

The stokes’ method allows each individual isolate to be compared with a sensitive control of the same or similar species which is subjected to the same technical conditions of medium, incubation time, atmosphere, temperature and disc content.

How do I prepare for MHA?

Preparation of MHA

  1. Suspend 38 gm of the medium in one liter of distilled water.
  2. Heat with frequent agitation and boil for one minute to completely dissolve the medium.
  3. Autoclave at 121°C for 15 minutes.
  4. Pour cooled Mueller Hinton Agar into sterile petri dishes on a level, horizontal surface to give uniform depth.

How do you analyze zone of inhibition?

Measure the diameter of the zone of inhibition for each disk. Keeping the lid of the plate in place, use a ruler to measure the diameter of the disk plus the surrounding clear area in millimeters (mm). Include the diameter of the disk in your measurements.

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How do you test the effectiveness of antibiotics?

Testing methods

Tests for antibiotic sensitivity include: Kirby-Bauer method. Small wafers containing antibiotics are placed onto a plate upon which bacteria are growing. If the bacteria are sensitive to the antibiotic, a clear ring, or zone of inhibition, is seen around the wafer indicating poor growth.

How is antimicrobial susceptibility test performed?


  1. Select a pure culture plate of one of the organisms to be tested.
  2. Aseptically emulsify a colony from the plate in the sterile saline solution.
  3. Repeat until the turbidity of the saline solution visually match that of the standard turbidity.
  4. Take a sterile swab and dip it into the broth culture of organism.

What is paper disc diffusion method?

The disk-diffusion agar method tests the effectiveness of antibiotics on a specific microorganism. An agar plate is first spread with bacteria, then paper disks of antibiotics are added. This method is used to determine the best antibiotic to use against a new or drug-resistant pathogen.

Why is disk diffusion technique not a perfect?

The disk diffusion technique is found unable to identify the performance potential of the antibiotics under in vivo conditions and the main reason for that is, some antibiotics are found unable to diffuse in this agar easily as every antibiotic has different diffusion potential.

What is meant by antimicrobial activity?

Antimicrobial activity refers to the process of killing or inhibiting the disease causing microbes. Various antimicrobial agents are used for this purpose. Antimicrobial may be anti-bacterial, anti-fungal or antiviral. They all have different modes of action by which they act to suppress the infection.

What is MIC in microbiology?

In microbiology, the minimum inhibitory concentration (MIC) is the lowest concentration of a chemical, usually a drug, which prevents visible growth of a bacterium or bacteria. MIC depends on the microorganism, the affected human being (in vivo only), and the antibiotic itself.

What factors influence the size of the zone of inhibition?

What factors influence the size of the zone of inhibition for an antibiotic? Diffusion of the antibiotic, the size of the inoculum, the type of medium, and resistance mechanism of organism.

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Why is Mueller Hinton agar used?

Mueller-Hinton has a few properties that make it excellent for antibiotic use. 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 of the antibiotics than most other plates.

How do you find the minimum inhibitory concentration?

  1. Determination of minimal inhibitory concentrations (MICs)
  2. Weight of powder (mg) =
  3. Volume of solvent (ml) X Concentration (µg/ml) / Potency of powder (µg /mg)

Beside this, how do you determine antibacterial activity?

Among these methods, the most common are listed below.

  1. Agar well diffusion method. Agar well diffusion method is widely used to evaluate the antimicrobial activity of plants or microbial extracts [32], [33].
  2. Agar plug diffusion method.
  3. Cross streak method.
  4. Poisoned food method.

Similarly, what is meant by antibacterial activity? Medical Definition of Antibacterial

Antibacterial: Anything that destroys bacteria or suppresses their growth or their ability to reproduce. Heat, chemicals such as chlorine, and antibiotic drugs all have antibacterial properties. Many antibacterial products for cleaning and handwashing are sold today.

What is the purpose of a control disk?

The control disk is there to show what it would be like if no antibiotics were used against the bacteria, showing its normal growth.

Furthermore, is the disk diffusion method measuring bacteriostatic or bactericidal activity explain?

Each antimicrobial agent inhibits growth differently (e.g. cell wall structure, permeability, and species). Is the disk-diffusion technique measuring bacteriostatic or bacterial activity? Measuring bacteriostatic because instead of killing the microorganisms they inhibit microbial growth.

What is agar dilution method?

Agar dilution involves the incorporation of different concentrations of the antimicrobial substance into a nutrient agar medium followed by the application of a standardized number of cells to the surface of the agar plate.

What is the zone of inhibition?

Measurement of the Zone of Inhibition of an Antibiotic. The Zone of inhibition is a circular area around the spot of the antibiotic in which the bacteria colonies do not grow. The zone of inhibition can be used to measure the susceptibility of the bacteria to wards the antibiotic.