Integron: A mobile DNA element that can capture and carry genes, particularly those responsible for antibiotic resistance. Integrons do this by site-specific recombination.
There are at least three classes of integrons based upon which integrase gene they contain. The antibiotic resistance genes that integrons capture are located on gene cassettes. These cassettes can exist as free circular DNA. A recombination event occurs, integrating the cassette into the integron. Additional gene cassettes can integrate, resulting in the integration of several genes.
Although gene cassettes are a mechanism for the development of multiple antibiotic resistance, bacteria predating the use of antibiotics have also been found to contain cassettes.