In parts of rural India, a strain of penicillin-resistant Streptococcus pneumoniae was identified in the early 1980's. It's
prevalence rapidly increased as the cause of serious pneumonia for several years. In 1986, three new antibiotics were
introduced and annually rotated to treat the penicillin-resistant strain. After ten years, the prevalence of the penicillin-
resistant strain has declined significantly, and resistance to the newly introduced antibiotics has not increased.
Which of the following describes the rise and decline in prevalence of penicillin-resistant Streptococcus pneumoniae in
this scenario?
Antibiotic resistance is not genetically mediated so an example of antibiotic resistance in bacteria is not an example of any kind of
selection.
Negative selection for penicillin-resistance left the bacteria more susceptible to penicillin and all other antibiotics after a sufficient
number of years of exposure.
Positive selection for penicillin-resistance caused the resistant bacteria to become the dominant strain until the penicillin was
removed as a pressure and the trait began to decline in prevalence.
Mosaic selection caused a new mutation to arise that made the bacteria resistant to penicillin, then another new mutation arose
that made the bacteria resistant to all antibiotics.
