Penicillin antibiotic has more effectiveness on gram-positive bacteria

Biology Report
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Introduction
Bacteria were some of the first organisms on our planet. They have evolved over time resulting in a variety of bacteria that are in existence today. They can be classified into two categories namely; gram positive and gram negative. This classification depends on the differential staining process referred to as Gram stain. The Gram stain classifies bacteria with respect to their ability to hold the violet color whenever decolorized by an organic solvent such as ethanol. This differential cell wall structure is also critical in determining the kind of antibiotics that are effective against them. The Gram stain retention is dependent on the bacterial cell membrane (Chudobova et al., 2014). The gram-positive bacteria have a two-walled membrane that helps retain the stain. Their cell membrane is composed of a cytoplasmic membrane and a cell wall. The cell wall is basically made up of peptidoglycan-polysaccharide that is important in providing the bacteria with resilience and rigidity (Clutterbuck et al., 2007). Additionally, this compound is useful for the bacteria’s capability to stain. On the other hand, gram-negative bacteria have three cell wall layers namely; the outer membrane, periplasmic space, and a cytoplasmic layer. The outermost membrane and cytoplasmic layer are made up of phospholipids. The peptidoglycan layer is situated in the periplasmic region and lacks teichoic acid. These factors render gram-negative bacteria irresponsive to gram staining.

There are different therapeutic regimens that help combat bacteria, penicillin being one of them. However, penicillin’s mode of action is limited to gram-positive bacteria (Tortora et al., 2004). It is known to inhibit the synthesis of these micro-organisms’ cell walls. This experiment, thus, seeks to understand why penicillin is more effective in gram-positive bacteria such as Staphylococcus aureus and not in gram-negative bacteria such as Escherichia coli. The independent variable will be the penicillin coated discs while the zone of inhibition will act as the independent variable.
The rationale of the experiment: Basically, the main aim of the experiment is to ascertain that indeed penicillin is more effective when used to combat gram-positive bacteria such as Staphylococcus aureus.
Hypothesis: Penicillin is more effective on gram-positive bacteria than on gram-negative bacteria.
Method
Using Kirby-Bauer Test
Swap sample of bacteria cover evenly on 2 plates which are gram-positive (Staphylococcus aureus) bacteria, and another is gram-negative (Escherichia coli) bacteria.
Divide each plate into four even quarters and place penicillin-coated-discs (independent variables) into two-quarters of each disc, and the rest spot will place water-coated-discs (control group).
Place the fresh plates in the incubator overnight at 37 degrees Celsius.
Results
Trials Zone of Inhibition (mm)
Gram + Anti Gram – Anti Gram + Control Gram – Control
1 18 3 3 3
2 17 3 3 3
3 19 3 3 3
4 18 3 3 3
Average 18 3 3 3
Std Dev. 0.8164966 0 0 0

After staying overnight, results collected show that penicillin coated disc placed in the gram-positive bacteria (S. aureus) sample plate had a larger zone of inhibition of an average of 18mm.
The other plates (including that with E. coli) had a significantly smaller zone of inhibition averaging 3mm each.
The standard deviation was 0.8164966.
Discussion
After incubation, the growth of bacteria was supposed to cover the whole of each bacterium sample, only leaving out the region around the penicillin-coated discs. This region is also known as the zone of inhibition (Harley, 2004). The longer or, the larger this region is an indication that penicillin was effective in inhibiting bacterial growth. This was the case with S. aureus which had a significantly larger region as compared to the other plates, including that with gram-positive E-coli. Hence, confirming our hypothesis that indeed gram positive are more susceptible to penicillin. This susceptibility is further explained by morphological differences between gram-negative and gram-positive as highlighted in the introduction part of the report.
Conclusion
Indeed, the penicillin antibiotic is more effective on gram-positive bacteria than in gram-negative bacteria as shown in the experiment results.
References
Chudobova, D., Dostalova, S., Blazkova, I., Michalek, P., Ruttkay-Nedecky, B., Sklenar, M., … & Konecna, M. (2014). Effect of ampicillin, streptomycin, penicillin, and tetracycline on metal resistant and non-resistant Staphylococcus aureus. International journal of environmental research and public health, 11(3), 3233-3255.
Clutterbuck, A. L., Cochrane, C. A., Dolman, J., & Percival, S. L. (2007). Evaluating antibiotics for use in medicine using a poloxamer biofilm model. Annals of Clinical Microbiology and Antimicrobials, 6(1), 2.
Harley, J. P. (2004). Laboratory exercises in microbiology. McGraw-Hill Science, Engineering & Mathematics.
Tortora, G. J., Funke, B. R., Case, C. L., & Johnson, T. R. (2004). Microbiology: an introduction (Vol. 9). San Francisco, CA: Benjamin Cummings.