10.5 Antibiotics
The E.coli responded to 3 of the 6 types of antibiotic. Therefore the hypothesis, that the E.coli is not tolerant of any of the antibiotics, was rejected. The E.coli was not affected by either Penicillin G or Ampicillin. This is because E.coli is a gram-negative bacteria and produces β -lactamase which an enzyme that breaks down the β -lactam rings of the penicillins. Because E.coli produces β -lactamase, it is able to prevent the β -lactams from the penicillin from destroying its cell membrane. Sulphatriad also did not inhibit the growth of E.coli. As discussed in the introduction, Sulfatriad is a bacteriostatic antibiotic that suspends the production of folic acid in all bacteria. However, because the E.coli was growing on nutrient agar, it is possible that the agar contained enough folate for the folic acid production process to be bypassed. Therefore the E.coli continued to grow. The chloramphenicol, tetracycline and streptomycin were all able to kill the E.coli bacteria. These three antibiotics inhibit the activity of enzymes that are instrumental in DNA and RNA synthesis. So the conclusion from the antibiotic test is that E.coli hasβ -lactamases and therefore cannot be killed by β -lactam antibiotics. Also, there was folate in the nutrient broth so the sulphatriad had no effecton the E.coli, and the best way to kill E.coli is to treat it with antibiotics that attack the DNA and RNA synthesising enzymes. To further improve this experiment, various other kinds of antibiotics with different mechanisms of action could be tested.
10.6 Further Research
There is further relevant research pertaining to the topic of optimal growth conditions and tolerances of E.coli bacteria. Research into E.coli’s compatibility with fungi and other bacteria would be helpful to explain anomalous results when other bacterial or fungal colonies are present in the test plates. Also, the growth rate of the E.coli under certain conditions (such as the variables manipulated in the experiments in this investigation) could be tested.