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Relatively short, semi-autonomous DNA segments that carry genes which protect bacteria from various environmental factors, such as heavy metals and antibiotics.
Resistance plasmids are an example of extrachromosomal encoding of resistance and they contrast, therefore, with chromosomal resistance. Because plasmids are an important means of horizontal gene transfer between bacteria, that is, as via conjugation, resistance plasmids represent a medically important means of acquisition of antibiotic resistance by bacterial pathogens.
The consequence of plasmids carrying resistance genes is that these genes are readily transferred between bacteria. The result is that bacterial resistance mechanisms can evolve in one strain or even species of bacterium and then be transferred into another another strain or species. Such transfer can result in the immediate acquisition of antibiotic resistance by the recipient strain.
Resistance plasmids often carry multiple resistance-encoding genes. As a consequence, bacteria can simultaneously acquire resistance to multiple antibiotics due to acquisition of only a single resistance plasmid.
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