Biology experiment: Antibiotics

Although we did this experiment a while ago (22nd March ) I’ve finally grabbed a moment to write about it.

The experiment involved producing a pour plate and since microbes are always present in the air, we worked around a lit Bunsen Burner which produced upward air movement to try to minimise the risk of contaminating the plates.

We produced two pour plates to investigate: one with Escherichia coli and the other using Micrococcus luteus. To both we added an antibiotic susceptibility testing ring and left the pour plates for a week.

Fig. 2 Pour plate using E. coli
Fig. 1 Pour plate using E. coli


Figure 1 shows the pour plate with E. coli. There are two very clear exclusion zones around the cefoxitin and streptomycin antibiotics which shows that these antibiotics were the most effective in killing the bacteria. Although the photo it is not very clear, you may still see a halo effect around the streptomycin and one reason for this may be antibiotic resistance. For me this was surprising to hear but also very enlightening on the issue of antibiotic resistance. If antibiotic resistant bacteria can be cultured in school on a simple pour plate, how are we going to control the increase of antibiotic resistant bacteria on a greater level, especially in the health industry? Although this has been an ongoing problem for a number of years, I don’t think I have ever realised the impact of this until one of my friends wrote a post about the subject. One of the main take away messages was that if the problem continues to grow, the practice of medicine is going to have to change. How can surgery be performed if the main way of treat bacterial infections is useless?

Fig. 1 Pour plate with M. luteus
Fig. 2 Pour plate using M. luteus

So, coming back to the pour plates. The other pour plate was less successful as M. luteus is very hard to culture and so the effect of the antibiotic is less noticeable. In addition the white ‘splodge’ that can be seen in Fig. 2 shows that the plate has been contaminated. It is most likely to be some form of fungi because on close observation the ‘splodge’ was furry.

Overall it was a very interesting experiment to carry out, not only because I have never produced pour plates before but also because of the results it produced.


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