The Use of Auxotrophs in the Laboratory

1. Introduction

Auxotrophs are microorganisms that require certain compounds that they cannot synthesize themselves and must be obtained from the environment. These requirements are generally in the form of specific amino acids, vitamins or other essential nutrients. The use of auxotrophic bacteria in the laboratory is widespread, as they provide a convenient way to select for or against specific mutants. One striking example of this is antibiotic resistance, which has become an increasingly serious problem in recent years as more and more strains of bacteria evolve to resist the effects of our drugs.

2. Methods

In this practical we used two different antibiotics, tetracycline and chlorampenicol, to test for their effects on different auxotrophs. The tetracycline-sensitive strain we used was Escherichia coli ATCC25922 and the chlorampenicol-sensitive strain was Salmonella enterica serovar Typhimurium ATCC14028. For both strains we grew them on Luria-Bertani (LB) agar plates supplemented with the appropriate antibiotic, as well as on plates without any antibiotic (control plates). We then incubated the plates at 37 degrees Celsius for 24 hours before counting the number of colonies that had formed.

3. Results and Discussion

As expected, both E. coli and S. enterica were able to grow on the control plates with no antibiotic present. When tetracycline was added to the LB agar plates, there was a significant reduction in the number of colonies formed by E. coli compared to the control plates, indicating that this strain is sensitive to tetracycline (Figure 1). In contrast, there was no significant difference in the number of colonies formed by S. enterica on tetracycline-containing plates compared to control plates, indicating that this strain is resistant to tetracycline (Figure 2).

When chlorampenicol was added to the LB agar plates, there was a significant reduction in the number of colonies formed by both E. coli and S. enterica compared to the control plates (Figures 1 and 2). This indicates that both strains are sensitive to chlorampenicol.

These results confirm that auxotrophic requirements can be used to select for or against specific traits in bacteria. In this case, we were able to select for antibiotic resistance by using tetracycline-containing plates for E. coli and chlorampenicol-containing plates for S. enterica. This highlights the importance of using a range of different antibiotics when testing for resistance, as different antibiotics will have different effects on different strains of bacteria.

4. Conclusion

In conclusion, this practical showed that auxotrophic requirements can be used to select for or against specific traits in bacteria. Antibiotic resistance is a major problem worldwide and this practical demonstrated how it can be selected for in the laboratory using auxotrophic bacteria. This highlights the importance of using a range of different antibiotics when testing for resistance, as different antibiotics will have different effects on different strains of bacteria

FAQ

Antibiotic resistance in bacteria is the ability of bacteria to resist the effects of an antibiotic.

Antibiotic resistance develops in bacteria when they are exposed to antibiotics. Over time, some bacteria develop mutations that allow them to survive even in the presence of an antibiotic.

The consequences of antibiotic resistance in bacteria include the spread of disease, as well as the development of new strains of bacteria that are resistant to all available antibiotics. This can make treating infections very difficult and expensive.

We can prevent or slow down the development of antibiotic resistance in bacteria by using antibiotics only when necessary, and by following the instructions for taking them exactly as prescribed. Additionally, we can develop new antibiotics to keep ahead of the development of resistance.