Escherichia coli bacterial culture undergoes exposure to ultraviolet (UV) radiation. Subsequently, the bacterial cells are cultivated on a complete medium, and 8 individual colonies (numbered 1 to 8) are chosen for further analysis. The complete medium plate is used to create four replica plates, which contain minimal medium or minimal medium added with one antibiotic (replica plates numbered 1 to 4). The results obtained are as follows:

Can you identify the colony or colonies that exhibit resistance to all the tested antibiotics?

• A. Colonies 1 and 8.
• B. Colonies 2 and 4.
• C. Colonies 3 and 7.
• D. Colonies 5 and 6.

Answer: (A)