Strain E. coli S. aureus Germicide Isopropyl Alcohol Lysol Fabuloso 10% 30% 50% 25% 50% 100% 25% 50% 100% G = Growth; NG = No Growth 3) Review the data for both bacterial strains. a. Which germicide was most effective against each strain and at what concentration? b. Which was the least effective? 4) Which bacterial strain do you think seemed to be most resistant to the germicides and why? 5) What were the purposes of the four controls? a. Control #1: b. Control #2: C. Control #3: d. Control #4
The Correct Answer and Explanation is:
3a. Which germicide was most effective against each strain and at what concentration?
E. coli:
The most effective germicide against E. coli is Lysol at a concentration of 100%. This is because at this concentration, there was No Growth (NG) observed, indicating the complete inhibition of bacterial growth. The data shows that as the concentration of Lysol increased, the effectiveness improved.
S. aureus:
The most effective germicide against S. aureus is Fabuloso at a concentration of 100%. Similarly to E. coli, this concentration led to No Growth (NG), indicating that it effectively eliminated the S. aureus bacteria.
3b. Which was the least effective?
E. coli:
The least effective germicide against E. coli was Isopropyl Alcohol at 10% concentration. At this low concentration, Growth (G) was still observed, indicating that the bacteria were not sufficiently killed or inhibited by this concentration.
S. aureus:
For S. aureus, Isopropyl Alcohol at 10% was also the least effective. Like with E. coli, this concentration did not sufficiently prevent bacterial growth, showing that it was ineffective at killing S. aureus.
4. Which bacterial strain seemed to be most resistant to the germicides and why?
S. aureus appears to be more resistant to the germicides, especially at lower concentrations. It shows growth at lower concentrations of Isopropyl Alcohol (10% and 25%) when compared to E. coli, which has more effective inhibition by those concentrations. S. aureus is generally more resilient due to its thick peptidoglycan cell wall, which makes it harder for some disinfectants to penetrate and kill the bacteria effectively. Additionally, S. aureus has been known to develop resistance to various types of disinfectants over time, which could also contribute to its resistance in this test.
5. What were the purposes of the four controls?
Control #1:
This could be a negative control, where no germicide is applied to the bacterial strain. The purpose of this control is to observe the natural growth of the bacteria without any interference and ensure that any growth observed is due to the bacteria’s inherent properties rather than experimental error.
Control #2:
This could be a positive control, where a known effective germicide or antibiotic is used to confirm that the experimental setup can successfully inhibit bacterial growth. This control serves as a benchmark to evaluate the effectiveness of the germicides being tested.
Control #3:
This could be a sterility control, where no bacterial strain is introduced, but the germicide is still applied. This ensures that there are no contaminants in the germicides or the medium used during the experiment.
Control #4:
This could be a vehicle control, where the solvent or carrier used to dilute the germicides (e.g., water or alcohol) is applied to the bacterial strain. This control helps assess whether the solvent itself has any inhibitory effect on bacterial growth.
Each of these controls is essential to validate the experimental results and ensure that observed effects are due to the germicides and not other variables.
