One strain of E coli is resistant to the antibiotic...

One strain of $E$ coli is resistant to the antibiotic streptomycin, and another strain is resistant to the antibiotic ampicillin. The two strains were cultured together and then plated on selective medium containing streptomycin and ampicillin. Several colonies appeared, indicating that cells had acquired resistance to both antibiotics. Suggest a mechanism to explain the acquisition of double resistance.

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Key Concepts

Horizontal Gene Transfer

Horizontal gene transfer is the process by which an organism incorporates genetic material from another organism without being its offspring. This mechanism allows bacteria to rapidly acquire new traits, such as antibiotic resistance, by transferring genes across different strains or species rather than through vertical inheritance from parent to progeny.

Conjugation

Conjugation is a specific form of horizontal gene transfer in bacteria that involves direct cell-to-cell contact. Through a pilus, a donor cell can transfer plasmids or other genetic elements carrying antibiotic resistance genes to a recipient cell, thereby potentially conferring resistance traits such as those needed to survive an antibiotic environment.

Plasmids

Plasmids are small, circular, double-stranded DNA molecules separate from a bacterial chromosome. They often carry genes that provide survival advantages, including antibiotic resistance. Plasmids facilitate the horizontal gene transfer of these traits through mechanisms like conjugation, effectively spreading resistance within bacterial populations.

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