Since antibiotic resistance of bacteria is becoming such a large and frequent problem, this research was conducted to determine if resistance in Escherichia coli could be induced by repeated exposure to ampicillin.
The procedure was based on a standardized method of testing resistance called the Kirby-Bauer (KB) Disk Diffusion Test. Brain-Heart Infusion (BHI) broth was labeled CØ for control and Tl-5 for tests. The broths were inoculated with E. coli. Ampicillin disks were added to the Test Group's BHI broths. After incubation, the BHI broths were sub-cultured to blood agar plates and Mueller-Hinton agar plates for the KB test. The plates were incubated, and the zones of inhibition read. The E. coli was then sub-cultured from the blood agar to the BHI, and the process was repeated until the E. coli showed significant resistance to the ampicillin.
The average rate of resistance of the CØ Group was 0 mm per day, because the zone diameters of the CØ Group stayed at 20 mm. The average rate of resistance of the Test Group was 3.2 mm per day. This data indicated that the CØ Group remained susceptible to the ampicillin throughout the experiment. The Test Group, however, did become resistant to the ampicillin.