In a study aiming to identify the gene responsible for antibiotic resistance in a bacterial strain, which of the following steps aligns with the principles of molecular Koch's postulates?

Comparing the growth rate of the bacteria in different culture media

Introducing a plasmid containing the suspected gene into a non-resistant strain

Measuring the change in antibiotic resistance after exposing the bacteria to UV light

Observing the physical characteristics of the bacteria under a microscope