Plasmids bacterial conjugation

DNA transfer of drug resistance Of particular clinical concern is resistance acquired due to DNA transfer from one organism to another. Resistance properties are usually encoded in extrachro-mosomal R factors (plasmids). These may enter cells by processes such as transduction (phage-mediated), transformation or, most importantly, bacterial conjugation. 

D. B. Clewell, Sex Pheromones and the Plasmid-Encoded Mating Response in Enterococcus Faecalis. In Bacterial Conjugation D. B. Clewell, Ed. Plenum Press New York, 1993 pp 349-367. 

Russi, S., Boer, R., and Coll, M., 2008. Molecular machinery for DNA translocation in bacterial conjugation, in Plasmids Current Research and Future Trends (ed. G. Lipps), Norwich, U.K. Caiser Academic Press. 

Genetic material can be transferred horizontally between bacterial cells either as free DNA by transformation or as plasmid DNA via conjugational... 

Resistance can emerge by mutation, though more commonly it is due to plasmid-encoded trimethoprim-resistant dihydrofolate reductases. These resistant enzymes may be located within transposons on conjugative plasmids that exhibit a broad host range, accounting for rapid and widespread dissemination of trimethoprim resistance among numerous bacterial species. 

Multicopy plasmids offer a limited, but still instructive comparison. Plasmids are replicating clusters of genes in bacteria. Under certain conditions they confer beneficial traits (such as resistance against antibiotics) on the bacterial host. They can also be passed on by conjugation between cells. A well elucidated mechanism of copy number control of abundant plasmids relies on a frans-acting inhibitor and czs-acting activator. For example, the ColE 1 plasmid in Escherichia coli blocks the action of the RNA primer (activator) by... 

---