ANTIFUNGAL ASSAY AGAR

Description

Fungal infections have been reported to have dramatically increased in the past decade, and these often occur as systemic infections or as co-infections with other diseases, such as AIDS or cancer, or in patients who are immunocompromised. Unfortunately, in addition to the limited number of antifungal drugs currently available, fungal infections tend to rapidly develop resistance to these drugs. For these reasons, fungal infections now show much higher mortality rates than bacterial infections. The rapid increase in fungal infections and the growing number of new antifungal agents indicate an increasing need for rapid and accurate methods for antifungal screening and susceptibility testing. Antifungal Assay Agar was formulated by Berger and Lazecka for convenience in assaying antifungal activity of pharmaceutical products and other materials by both base and seed layers for assays by cylinder plate or disc methods. Assay Methods Cylinder plate method: This method was first devised by Abraham et al and later modified by Schmidt and Moyer and it depends upon diffusion of the antibiotic from vertical steel cylinders placed on the surface of inoculated agar medium. This produces zones of inhibition around the cylinder containing antibiotic solution depending upon the concentration of the antibiotic in the cylinder. This method is commonly employed in the assay of pharmaceutical preparations of Penicillin and other antibiotics. For assay, use Petri plates with 20 x100 mm dimension and stainless steel or porcelain cylinders with the outside diameter 8 mm, inside diameter 6 mm and length 10 mm. All dimensions should have a tolerance of 0.1 mm. The cylinders should be carefully cleaned to remove all the impurities. For assays requiring base and seed layer, the base layer is allowed to solidify first and then overlaid with the seed agar containing the proper concentration of the test organism. Most assays require base layer of 21 ml and seed layer of 4 ml. Generally, 6 cylinders are used per plate. The cylinders are placed on inoculated plates at equal distance. Paper-disc method: Paper discs with a diameter of 9 mm are impregnated with the antibiotic solution and placed on the culture medium. Antibiotic can also be applied to the disc after it has been placed on the medium. Plates containing a single layer of medium with 2 mm thickness may be used for these tests. All other steps are similar to the cylinder plate method.