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Horizontal Gene Transfer

Horizontal gene transfer, or the process of swapping genetic material between neighboring “contemporary” bacteria, is another means by which resistance can be acquired.  Many of the antibiotic resistance genes are carried on plasmids, transposons or integrons that can act as vectors that transfer these genes to other members of the same bacterial species, as well as to bacteria in another genus or species.  Horizontal gene transfer may occur via three main mechanisms: transformation, transduction or conjugation.

Transformation involves uptake of short fragments of naked DNA by naturally transformable bacteria. Transduction involves transfer of DNA from one bacterium into another via bacteriophages.  Conjugation involves transfer of DNA via sexual pilus and requires cell –to-cell contact.  DNA fragments that contain resistance genes from resistant donors can then make previously susceptible bacteria express resistance as coded by these newly acquired resistance genes. 




 Trivia: Conjugation and Plasmids

Conjugation was first described in 1946 by Lederberg and Tatum, based on studies showing that the intestinal bacteria E.coli uses a process resembling sex to exchange circular, extrachromosomal elements, now known as plasmids.  (Torrence and Isaacson, 2003)


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