Which one of the following will least likely result from the overuse of antibiotics?

a Direct alteration of DNA sequence in a bacterium to gain antibiotic resistance b Direct transfer of an antibiotic-resistant gene from a bacterium to a non-resistant bacterium c Incorporation of an antibiotic-resistant gene in a bacteriophage d Incorporation of an antibiotic-resistant gene in a non-resistant bacterium e Reduction in the total number of antibiotic-sensitive bacteria