How can antibiotics allow resistant bacteria or fungi to multiply?

Antibiotics can facilitate the multiplication of resistant bacteria and fungi through a process of selective pressure. When an antimicrobial agent is administered, it typically kills or inhibits the growth of sensitive microorganisms.12

This process leads to the following outcomes:

• Elimination of Competition: By eradicating sensitive organisms, antibiotics remove the natural inhibitory pressure these microbes exert on one another. With their vulnerable competitors reduced or eliminated, surviving resistant strains face less competition for resources, allowing them to proliferate.13
• Selective Survival: Bacteria that possess natural resistance—whether through spontaneous mutations or the acquisition of resistance genes via conjugation or transduction—are not affected by the drug. These resistant organisms survive the treatment and continue to reproduce, eventually becoming the dominant population.123
• Opportunistic Growth: In some cases, organisms that are generally resistant to antibiotics, such as yeast, can increase to numbers sufficient to invade and infect tissue once the normal microbial balance is disrupted.1

It is ethically imperative to use antibiotics judiciously, as their indiscriminate use accelerates the development and spread of these dangerous, drug-resistant populations.132