Integrons and the Origin of Antibiotic Resistance Gene Cassettes Super integrons with thousands of gene cassettes may have set the stage for pathogens to develop antibiotic resistance very rapidly

Integrons, which are natural genetic engineering platforms, can incorporate open reading frames and convert them to functional genes by ensuring correct expression. Although such integrons play a major role in multidrug resistance phenomena among gram-negative species, similar platforms occur in numerous bacterial species, where they can play other roles. Meanwhile, we have evidence suggesting that they are a major source of multidrug resistance integrons and their resistance gene cassettes observed in clinical isolates. Recruiting exogenous genes represents a rapid adaptation against antimicrobial compounds, and the integron functional platform seems perfectly suited for capturing those specific genes that enable bacterial pathogens to face challenges posed by multiple antibiotic treatment regimes. With the discovery of the superintegron and the thousands of cassettes entrapped in integrons of environmental species, we now have a better view of the immense resources embedded within this system. However, several questions of importance about this system are still without satisfactory answers, including insights about specific recombination processes, cassette genesis, and cassette exchange dynamics within complex bacterial populations.