A bacterial infection is treated repeatedly with the same

antibiotic. Each episode resolves clinically, but relapse occurs after

treatment cessation. The causative strain shows no increase in MIC and no

detectable resistance mutations. Further investigation reveals a persistent

subpopulation that survives antibiotic exposure through metabolic inactivity.

Assuming repeated antibiotic exposure over time, what type

of selection pressure is most likely acting on the bacterial population?