In 1980, only 1% to 5% of all Staphylococcus aureus isolates were MRSA strains. Now 60% to 70% of S. aureus isolates are MRSA strains. This is an example of
A) stabilizing selection of humans.
B) directional selection of humans.
C) directional selection of bacteria.
D) diversifying selection of bacteria.

Question

Quizplus · Accepted Answer

The increase in the proportion of MRSA strains indicates that there has been selection pressure favoring the survival and reproduction of bacteria with antibiotic resistance. This is an example of directional selection of bacteria, where the selective pressure (antibiotics) favors traits that increase the fitness (antibiotic resistance) of certain individuals (MRSA strains) within the population.

In 1980, Only 1% to 5% of All Staphylococcus Aureus