Resistance to an antibiotic can be transferred from a resistant to a susceptible organism by?

The transfer of antibiotic resistance from a resistant organism to a susceptible one primarily occurs through mechanisms involving genetic elements called plasmids. Extrachromosomal plasmids are small, circular DNA molecules that exist independently of the chromosomal DNA within a bacterium. These plasmids often carry genes that confer resistance to antibiotics and can be easily transferred between bacteria through processes such as conjugation, transformation, or transduction.

When a resistant bacterium containing a plasmid with resistance genes encounters a susceptible bacterium, the plasmid can be transferred through direct contact, allowing the susceptible bacterium to acquire the resistance trait. This means that the previously susceptible organism can now survive in the presence of the antibiotic, contributing to the spread of resistance within microbial populations.

While selective pressure can lead to the proliferation of resistant strains in the presence of antibiotics, it does not facilitate the actual transfer of resistance genes between organisms. Mutation can play a role in developing resistance within a single organism but does not account for the horizontal gene transfer that occurs between different organisms. Innate passage is not a recognized mechanism for the transfer of resistance; hence, the primary and most efficient route for sharing antibiotic resistance is through the action of extrachromosomal plasmids.