lab report example

lab report example

Analyzing the Effectiveness of Different Antibiotics in Inhibiting Bacterial Growth: A Comprehensive Laboratory Report

1. Introduction

B. Abstract of report: In this laboratory experiment, Escherichia coli and Proteus vulgaris served as the model Gram-negative bacteria for analyzing the overall efficiency of various antibiotics at inhibiting their growth, as well as the underlying mechanisms. Our experiment demonstrated that a number of antibiotics targeted cellulose synthesis, and that the inhibition of cellulose synthesis caused defects in bacterial division. The delay in division led to extended filaments, which were correlated with increased sensitivity of the coiled bacteria to aztreonam. Additionally, the level of nucleoid construction was also observed to be associated with the cell division. The nucleoid construction reflects the intracellular state of the bacterial cell, and we suggest that the level of nucleoid construction determines the cell cycle and the effects of antibiotics that target MreB, FtsZ, and FtsI. Our results suggest an alternative clinical explanation that can be transposed into the field of antibacterial agents. Thus, our findings could guide future studies and development of new antimicrobial therapies.

A. Comments of author: For our honors biology final project, my lab group will conduct an experiment to analyze the effect of a selection of different antibiotics on bacterial growth. In our experiment, we are planning on testing the effectiveness of these antibiotics: erythromycin, minocycline, tetracycline, sodium azide, carbenicillin, gentamycin, ampicillin, and streptomycin. The effectiveness of an antibiotic for inhibiting bacterial growth is influenced by the mechanism of action of the antibiotic and the species of the bacteria. Bacteria have developed resistance to antibiotics because of the overuse and misuse of drugs, incompatibility of the drug with a resistance gene, and natural selection. The way bacteria develop resistance is when a cell is exposed to an antibiotic, the bacteria have proteins called efflux pumps and enzymes, which break down the structure of the antibiotic, allowing that cell to survive and subsequently reproduce, but the reproduction happens so quickly, due to a short generation time that make high mutation rates, and offspring have the same resistance as the parent cell. Antibiotics were once thought to be a near cure-all for most bacterial illnesses, but problems with misuse and overuse have made them less useful.

2. Materials and Methods

The bacteria employed in this lab were Bacillus cereus, Micrococcus luteus, Salmonella enterica, Serratia marcescens, and Escherichia coli. The bacteria cultures were prepared before the actual testing started. The test results were transferred into a computer program called Spectrophotometer created by the Open University. The effectiveness of the spectrophotometer readouts was tested to determine if the data collected during the previous procedures is correct. The potential sources for error in the previous experiments, including both human errors and instrumental errors, and the relevance of the findings are mentioned in greater detail in the discussion section. The procedures employed for this lab followed the instructions outlined in the published lab handout.

The materials that have been used in this lab report include test tubes, various antibiotics to be tested, brain heart infusion agar plates and agar slants, pipettes, microorganism swabs, spectrophotometer, bacteria cultures, distilled water, cuvettes, and plastic bags. The control group included the plain bacteria solution and the brain heart broth. A total of six test groups included penicillin-G, streptomycin, ciprofloxacin, tetracycline, chloramphenicol, and the special compound Mar-382. The susceptibility of the bacteria was tested on agar plates, the precision of the spectrophotometer was tested, and the effectiveness of each of the six antibiotics was determined using a series of procedures. The following aspects were measured while testing the effectiveness of the last antibiotic.

Section 2: Materials and Methods

3. Results

There was less general inhibition between the two E. coli cultures than the two S. epidermis cultures. When comparing treatments for the E. coli strain, with our first strain, the order of effectiveness from most effective to least effective treatments was as follows: ciprofloxacin, penicillin, tetracycline. With our second strain, the order of effectiveness from most effective to least effective treatments was as follows: ciprofloxacin, penicillin, tetracycline. When comparing treatments for the S. epidermis strain with our first strain of bacteria, ciprofloxacin was the most effective (with the largest decrease in optical density), followed by penicillin and tetracycline. With the second strain, the order of effectiveness from most effective to least effective treatments was as follows: penicillin, ciprofloxacin, tetracycline.

The growth of the two different strains of bacterial cells was observed in culture over a period of 24 hours. The decrease in optical density on the graph indicates an inhibition of growth. The data collected indicates the fastest rate of growth occurred in the culture not being exposed to any antibiotics. This was true for both strains of E. coli as well as both strains of S. epidermis. Next, the data collected indicates ciprofloxacin is the most effective antibiotic in hindering bacterial growth, as the cultures exposed to this drug did not reach an optical density as high as the other antibiotics. The least effective antibiotic in hindering bacterial growth was tetracycline. This drug did not have the largest decrease in optical density.

4. Discussion

The Kirby-Bauer test was originally designed for classifying species of bacteria based on their sensitivities to different antibiotics. In the results obtained in the laboratory, it was shown that a microorganism either resisted the substance (i.e., resistant) or it did not (i.e., susceptible), which helps greatly in the specific treatment of bacterial infections. With the unprecedented spread of antibiotic-resistant bacterial pathogens and the decreasing supply of new antibiotics, the K-B test is important and efficient in the preliminary screening of different antibiotics.

Three antibiotics – amoxicillin, streptomycin, and tetracycline – were tested on two different types of bacteria: E. coli and S. epidermidis. Most antibiotics have inhibitory effects on only certain types of bacteria, based on the cellular structure of the bacteria. The factor that contributes most heavily to the cellular structure of a bacterial cell is the presence of a cell wall. The antibiotics amoxicillin, streptomycin, and tetracycline are only effective against bacteria because of the differences in the cell structures of bacteria and mammalian cells. When these antibiotics are ingested by bacteria, amoxicillin inhibits the final transpeptidation step of peptidoglycan synthesis in bacterial cell walls, tetracycline inhibits the binding of aminoacyl-tRNA to the 30S ribosomal subunit, and streptomycin causes messenger RNA misreading in prokaryotes and premature stop codon induction.

5. Conclusion and Future Directions

Overall, the analysis shows that streptomycin, tetracycline, and kanamycin were the most effective antibiotics out of the ten tested, while the least effective were rifampicin, erythromycin, and chloramphenicol. They had some effect at lower levels, but as the antibiotic concentration increased, the drugs were unable to control bacterial growth. When we increased the levels of antibiotic, they lost considerable efficiency. For future directions, there are several different things that could be done. For one, this same experiment could be conducted, but with different types of antimicrobials. If successful, this could allow for the creation of more agar plates, with the inclusion of continuous levels of the most effective and acceptable antimicrobial. This would allow you to create a more specific graph and notice at what level the antibiotic was most effective in preventing the spread of the bacterium. In turn, this could allow for the creation of pills that had a slow release of the antibacterial property, which would help to combat drug resistance.

The primary goal of the study was to analyze the effectiveness of different antibiotics in inhibiting bacterial growth. This was successfully achieved. The study found that streptomycin and tetracycline were very effective in inhibiting bacterial growth. Kanamycin also performed well, but when observing the plates containing higher levels of the antibiotic, there was limited bacterial growth and a brownish coloring. Additionally, when drawing the graph for kanamycin and the data was represented as the level of antibiotic present, it was clear that the bacterium did not grow in higher levels of antibiotic. For rifampicin, erythromycin, and chloramphenicol, the antibiotic was very effective at low levels. However, upon reaching higher levels, the bacterium experienced little to no disruption in growth. Additionally, when creating HeLD agar plates, care should be taken to use the dispenser properly to avoid the creation of bubbles.