Question

A new bacterial infection is spreading through a city. Doctors start prescribing penicillin but they soon find that the bacteria is resistant to the antibiotic. Testing reveals that a penicillin resistance gene is located on a plasmid that is increasing in the bacteria population through conjugation and selection due to the use of penicillin. Doctors start using rifampicin, another antibiotic that works through a different mechanism than penicillin.
Which of the following is most likely to occur in the bacteria population?

• A. All bacteria without the penicillin resistance plasmid will be eliminated from the population by the use of rifampicin.
• B. The penicillin resistance plasmid will be eliminated from the population in several generations due to lack of use.
• C. The penicillin resistance plasmid will continue to increase in the population because it will protect against rifampicin.
• D. The spread of the penicillin plasmid will slow, but it will remain in the population.

Answer 1

Answer: (D)

The spread of the penicillin plasmid will slow, but it will remain in the population.

Plasmids are not transferred during reproduction, they are transferred through a mechanism of horizontal gene transfer from a donor cell to the recipient cell through a process called conjugation. Since the environment lacks the stimulus in the form of the drug, the plasmid will not be transferred to the bacterial cells that do not have them

So, the correct answer is 'The spread of the penicillin plasmid will slow, but it will remain in the population'