Answer:
This is antibiotic resistance. It occurs with over use of antibiotics.
When antibiotics are over used, likely targeted bacteria are being killed constantly even in absence of an infection. However, few bacteria may resist the antibiotics effects(selective pressure) , and therefore survived. If these resistant bacteria who were able to survive the selective pressure reproduce, they pass the resistant trait/ gene into their offspring.
Therefore with continuous exposure to antibiotics, they will resist the antibiotics effects(selective pressure),and thus reducing the effectiveness of antibiotic treatments with subsequent application.
Step-by-step explanation: