Methods to Test Antifungal Sensitivity

Antifungal preparations, or fungicides, are a class of chemical compounds that are used to kill fungi. Fungicides can also be biological agents. They are useful in killing fungi that can cause disease in plants and thus limit the full production of food. Fungicides are also useful for the human body which is prone to fungal infections, especially on the skin. A full range of fungicides is available on the market, so it is helpful to know how to test the sensitivity of these anti-fungals.

Testing Antifungal Sensitivity

• Sensitivity or susceptibility to fungicides is important so you will know whether a certain family of fungicide is effective in killing the fungus at which it is targeted. When a fungus becomes resistant to the fungicide, it can continue with its work, destroying crops or causing infections in humans. Researching methods of countering resistance to drugs has acquired greater importance following the wholesale resistance that fungi developed to a class of fungicides in the 1980s.
  Three popular methods of testing a fungus' sensitivity to fungicides exist: the disk agar gradient method, the E test method and the broth microdilution test. The latter is more useful in testing the resistance of antibiotics than the effectiveness of antifungals, so it is not commonly used.

Methods

• The disk method is well suited to determine the susceptibility of fungi to an antifungal agent called fluconazole. To begin the disc test method, you should melt and pour three glucose agar plates. Then prepare an inoculated plate that contains the fungus being tested by suspending it in about 5 ml of normal saline. Insert a cotton swab into the sample. Shake off the excess fluid by rubbing it inside the bottle or tube. Use the sample to streak the surface of the prepared plate in all four directions at 90 degree angles so all the surfaces are covered. Then dry the surface of the glucose plates at 35 degree C and incubate the plates for 24 to 48 hours.
  In the E test method, the procedure is the same, except that just one plate of agar is needed. Use a couple of forceps sterilized in flame to apply the E test strip and a neo-sensitab of the agent to be tested into the surface of the inoculated plate in such a way that there is contact with the agar.

Choosing a Method

• Each of the testing methods has its own advantages and disadvantages. While the broth microdilution method is useful for one class of fungus, the E test is more versatile and simpler, and can be effective against a class of fungi called Candida. However, it is more expensive, and is not known to be a correct barometer for defining the susceptibility of fungi to fluconazole. As stated, the disk method is good for this.