This is factually incorrect. Studies of bacterial adaptation start with a single cell. Any adaptation occurs as a result of mutation.
What do you have in mind when you refer to bacterial species?
When refering to a bacterial species, I am refering to the culture.
Every mutation was one within the confines of its own genetic makeup.
Killing so many of one strain within a culture only provides that those mutations are no long represented in the numbers they once were.
It is still the same culture, regardless of it’s cellular population.