Antibiotic Resistance Plasmids in Bacteria

Abstract Antibiotic resistance plasmids are bacterial extrachromosomal elements that carry genes conferring resistance to one or more antibiotics. They are notorious for their ability to transfer by conjugation between bacterial species and are significantly involved in the emergence and dissemination of multiple drug resistance associated with bacterial infections in humans. The information provided here includes some of the history and nature of antibiotic resistance as well as how plasmids have become significantly involved as intercellular carriers via the phenomenon of bacterial conjugation. The manner by which resistance determinants are able to move onto plasmids via their initial association with transposons and integrons is discussed. The existence of elements with both transpositional and conjugative properties, such as the conjugative transposons and integrative conjugative elements, is also noted. Key Concepts: Multiple antibiotic resistance represents a serious and growing clinical problem with regard to bacterial infections in humans. Resistance genes are commonly found on plasmids, which are small extrachromosomal elements commonly found in bacteria. Plasmids can vary widely with regard to their size and copy number in the cell. Plasmids are commonly able to move from one bacterial cell to another by a mechanism known as conjugation, which involves cell‐to‐cell contact followed by transfer of a copy of plasmid DNA from a donor to a recipient. Genes conferring antibiotic resistance are commonly found on elements known as integrons and transposons, which facilitate movement between different replicons such as between the bacterial chromosome and a plasmid. Some transposable elements, known as conjugative transposons, also carry resistance traits; and, although unable to replicate autonomously, they can move from one bacterial cell to another by a plasmid‐like mechanism. Excessive use of antibiotics in the treatment of human infections has, over time, contributed to the emergence and selection of resistant bacteria in the gut, a phenomenon that includes passage of resistance traits between nonpathogens and pathogens.