Description
The goal of an antimicrobial susceptibility test is to predict through an in vitro assessment the likelihood of successfully treating an infection with a particular antimicrobial agent. There are several continual or novel methods for performing antibacterial susceptibility testing. These include the disk diffusion test, broth microdilution, agar gradient and rapid automated instrument methods. Hi-Sensitivity Test Agar, which is used for antimicrobial susceptibility tests, is a semi-defined medium in which the mineral contents have been stabilized to give reproducible results. The thiamine and thymidine content is very low thus making it most suitable for testing antimicrobial activity of sulphonamides. However, some mutant strains which are totally dependent on thiamine and thymidine for their growth, will not grow on Hi-Sensitivity Test Agar, due to very low levels of these compounds in the media as they are the naturally occurring antagonist of trimethoprim. These strains should be carefully recognized. High-Sensitivity Test Agar has been so designed to overcome the problems occurring in Mueller-Hinton Media that are as follows. 1.Mueller Hinton Agar and Mueller Hinton Broth give different MIC values. 2.Mueller Hinton Agar shows antagonistic effect towards tetracycline. 3.High levels of sulphonamide and trimethoprim antagonists. 4.Media prepared using peptone of different manufacturers give poor reproducibility. 5.Poor growth supporting ability for Streptococci and variable growth rates with gram-positive organisms. Some pathogenic organisms are nutritionally dependent due to their intrinsic demands for special growth factors.
