Antibiotic Sensitivity Testing - Essay Example

Many antibiotics are undergone modifications that change their inherent characteristics such as reduced toxicity, increases solubility, thus giving them the desirable features that they lack being natural.
There are several methods developed to test the susceptibility of microorganism towards antibiotics including the Cup Borer method, the Ditch method and the Disc Diffusion method. The principle of the disc diffusion method is that when a filter disc is impregnated with a chemical that is placed on the agar, the chemical in the agar diffuses around the disc. The solubility of the chemical and its molecular size determines the size of the area of chemical infiltration around the disc. When an organism is placed on the agar around the disc, if it is susceptible to the chemical then there would be no growth around the area where the chemical is diffused and this area is called the “zone o inhibition”.
This inhibition can be measured and compared with a standard control strain and normal tables, Stokes and Kirby-Bauer method respectively. The factors that affect this method are the concentration of the bacterial inoculums, the depth and types of agar, the incubation conditions and the time of incubation. All these factors should be always taken into account while performing the test. An alternative test that can be performed is the determination of the amount of antibiotic required to either inhibit the growth of an organism or to kill the organism which is done by incubating a fixed concentration of the organism in increasing concentrations of antibiotics and checking for growth after 24h of incubation.
The assigned culture was swabbed onto the agar plate in three directions for maximal coverage. The plates were allowed to settle for 10 mins, followed by impregnating the antibiotic discs by pushing the dispenser over the agar. The antibiotic and the disc code were noted and the plates were kept in an incubator at 37⁰C.