Antibiotics and Resistance

ANTIBIOTICS AND RESISTANCE

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Abstract

The main aim of this experiment was to determine how the growth of E. coli would be like in different concentrations (growth media) that contained different antibiotics. After the experiment, it was determined that the optimal growth temperature of E. coli is 370 and that different antibiotics vary in their efficacy. Bactericidal antibiotics are used to kill bacteria directly while bacteriostatic antibiotics are used to suppress the growth of bacteria.

Introduction/theory

Over the course of human civilization, bacterial infections and diseases have been found to be the major causes of morbidity and mortality in the society. The synthesis and identification of synthetic chemicals with the ability to kill selective microbes, are some of the ways in which their impacts was reduced in the 20th century. The identification and purification of antimicrobial natural products was also another way in which bacterial infections and diseases were reduced. Over time, scientists and medical experts have researched and developed other more effective antibiotics.

However, the main challenge is that the bacteria’s mechanism eventually evolves to resist the drug. The antibacterial agents that are used medically or pharmaceutically vary in forms; disinfectants, antiseptics and antibiotics. Disinfectants are used to treat inanimate objects and a good example of that is bleach while antiseptics are used to inhibit or control microbe growth and a good example of this is alcohol. Antiseptics can also be applied directly into the living tissues such as to sanitize wounds. Antibiotics on the other hand are usually used for humans and kill cells selectively to inhibit the activities carried out by bacteria. Occasionally, antibiotics have been created as broad spectrum although some of them as narrow spectrum. Varying bacterial species require varying concentrations of the drugs so that the antibiotic can enhance its efficacy.

Purpose

The main aim for this experiment was to use E. coli to test the dosage effect as well as the mode-of-action of two antibiotics. The experiment also aims towards testing the antibiotic susceptibility of several species of opportunistic pathogen by checking and analyzing the previous week’s plates using the disc diffusion method or rather, Kirby-Bauer method.

Apparatus

1. Ethanol- control
2. 0.5 ug/ml chloramphenicol
3. 5 ug/ml chloramphenicol
4. Methanol- control
5. 0.2 ug/ml rifampicin
6. 2 ug/ml rifampicin

Procedure

1. A pre-inoculated culture of E. coli in nutrient broth was obtained in a test tube.
2. OD600 of the culture was read by withdrawing 3 ml of the culture, followed by adding to a cuvette to measure and returning the sample to the vessel immediately after it was read. Each OD was measured alongside the time of measurement relative to the time the treatment was added.

NB/ Proceed with the next step if OD600 is ≥0.2. However, if it is ≤0.2, it is advised that the flask be incubated by shaking at 37◦C and then taking the reading of the culture using a spectrophotometer after every 20 minutes until it reaches ≥0.2.