Enterococci are bacteria that are included in the intestinal flora of humans and are relatively harmless. One method Enterococci maintain a symbiotic relationship is by hydrolyzing esculin in the presence of bile (Susan L. Fraser, 2012). However Enterococci are in the top three-nosocomial infections. When infected, enterococci can cause numerous infections such as urinary tract infection coupled with fever (Susan L. Fraser, 2012). More specifically, Enterococcus Faecalis causes urinary tract infections.
Enterococcus Faecalis (E. Faecalis) is a gram-positive bacteria that is difficult to eliminate. With an increasing dependency on antibiotics, E. Faecalis is becoming feared due to its intrinsic antibiotic resistance (Wesley Glick, 2000). This strain is naturally immune to weaker levels of penicillin because of its ability to synthesize cell wall components in the presence of penicillin. Instead of allowing this antibiotic to destroy the cell wall, E. Faecalis produces penicillin-binding proteins that inhibit penicillin from disintegrating its cell wall (Susan L. Fraser, 2012). Thus a more effective antibiotic must be used.
For the purposes of this study, Penicillin, Tetracycline, and Ampicillin have been chosen to counter E. Faecalis. Based on a previous study completed by Wesley Glick, E. Faecalis is intrinsically resistant to weak Penicillin and Tetracycline (Wesley Glick, 2000). Therefore a hypothesis can be generated stating that Penicillin and Tetracycline will be partially ineffective towards eliminating E. Faecalis. However, since the Penicillin and Tetracycline used in this experiment are more potent, it is predicted that all three antibiotics will be effective against E. Faecalis, with Ampicillin exhibiting the largest zone of inhibition. Materials
Enterococcus Faecalis was taken from a stock sample and was spread across a blood agar plate. The plate was divided into four quadrants: three for antibiotics and one for control. A small disk was chosen, each containing one antibiotic of Penicillin, Tetracycline, or Ampicillin and placed at the center of each quadrant on the blood agar plate. The plate was sealed with tape, and was left to incubate at 37°C for twenty-four hours. Then the plate was left in a refrigerator for one week. After, the agar plates were taken out for observation. The zone of inhibition, or region around the antibiotic disk absent of bacteria, was measured and recorded for each quadrant (General Biology Laboratory Manual, 2010).
To determine if the bacteria was gram-positive or gram-negative, a slide must be prepared. A sample of E. Faecalis was swabbed onto a slide and then first stained with crystal violet. After about one minute, the slide was rinsed with water and then gram iodine was poured onto the slide. Once again the smear was rinsed with water only this time a 95% alcohol/acetone solution was placed onto the slide briefly and then rinsed off with water. Finally Safranin was dropped onto the slide for one minute and then the slide was rinsed with water yet again. The slide was finally blotted dry (General Biology Laboratory Manual, 2010).
The incubated blood agar plate revealed noticeable differences between the four quadrants. Quadrants one through three exhibited a zone of inhibition because of the presence of antibiotics, but quadrant four was control and allowed normal growth. 1
Figure 1: Zones of inhibition produced by the antibiotic disks in a culture of Enterococcus Faecalis. (1-Ampicillin, 2-Penicillin, 3-Tetracycline, 4-Control)
The Ampicillin disk produced the largest zone of inhibition, measuring at 20.8 mm with a standard deviation of 1.304mm. The Penicillin had the second largest size, measuring at 15.8 mm with a standard deviation of 0.837mm. And the Tetracycline disk nearly...