Natural Selection Question 2

MRSA is the acronym for methicillin-resistant Staphylococcus aureus. Many of the strains of the common bacterium are also resistant to other antibiotics in use today. The resistance is linked to a collection of genes carried on plasmids that are passed from one bacterium to another by conjugation. Suppose a newly discovered, chemically different antibiotic is used in place of methicillin. Which of the following would be the most likely effect on Staphylococcus aureus antibiotic resistance?

The gene for methicillin resistance, no longer needed, would disappear entirely from Staphylococcus aureus populations within a few generations.

Transmission of the methicillin-resistance plasmid by conjugation would increase among the Staphylococcus aureus population as the genes would confer resistance to the new antibiotic.

Transmission of the methicillin-resistance plasmid would gradually decrease but the plasmid would not entirely disappear from the Staphylococcus aureus population.

Transmission of the methicillin-resistance plasmid by conjugation would increase among the Staphylococcus aureus population due to destruction of bacteria without the plasmid through use of the new antibiotic.