The Antimicrobial Effects of Antibiotic Drugs: Lab Report

Topic: Pharmacology
Words: 463 Pages: 1
Table of Contents


The academic goal of the present experiment was to study the antimicrobial effects of two antibiotic drugs to inhibit bacterial growth. The objects of study were Gram-negative E. coli and Gram-positive S. epidermidis. The choice of prokaryotes from two different classifications was not a case, but on the contrary, was an essential goal of the experiment since it was expected that the effect of antimicrobial drugs was different depending on the structure of the bacterial cell wall. The antimicrobial activity of the drugs was analyzed by the Kirby-Bauer method when cultures were inoculated on a nutrient agar medium in vertical tubes. The lesson learned from this experiment is to recognize the difficulty of selecting a unique medical drug to inhibit bacterial growth.


The central result of the experiment was the measurement of the disk diameter for two bacteria depending on the type of antibiotic used. A summary of the diameters is shown in Table 1 below. Note that different concentrations of the drug were used: 10 units Bacitracin and 30 μg Tetracycline; in addition, a control was used to compare results. Interpretation of the disc diameters was performed according to the training Methodology of the experiment describing the patterns of antibiotic resistance for the two drugs.

Treatment Disk Code E. coli S. epidermidis
Zone Diameter (mm) Response (R, I, or S) Zone Diameter (mm) Response (R, I, or S)
Bacitracin B 10 4 R 21 S
Tetracycline TE 30 11 I 12 R
Control blank 0 R 0 R


Based on the results, the difference in the growth of bacterial lines under two different conditions compared to controls is remarkable. A larger disc size was associated with suppression of bacterial growth, whereas a smaller diameter signified resistance of the prokaryotes to the drug action of the substance. For E. coli, it was shown that the disc diameter was minimal in the Bacitracin medium and intermediate in the Tetracycline medium. From this, it could be concluded that the Gram-negative bacterium showed resistance to Bacitracin and relative resistance to Tetracycline. For Gram-positive S. epidermidis, the results were alternative: growth suppression by Bacitracin and resistance to Tetracycline. Consequently, it is reasonable to assume that Bacitracin is effective against Gram-positive bacteria, as confirmed by studies (Hong et al. 4691). Improvements for future studies consist in the use of photographs as additional evidence in the Results section. In addition, it is suggested that the range of drugs used to be expanded.


The present laboratory experiment is of high practical value because it reflects the current trend of increasing antibiotic resistance among pathogens. Testing two antimicrobials at once strengthened our critical thinking skills and allowed us to measure their effectiveness qualitatively. The work was an exciting experience that will be useful for future professional activities.

Work Cited

Hong, Wei, et al. “Synthesis, Construction, and Evaluation of Self-Assembled Nano-Bacitracin A as an Efficient Antibacterial Agent in vitro and in vivo.” International Journal of Nanomedicine, vol. 12, 2017, pp. 4691-4708.

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