Resistance bacterial conjugation

Many applications of the aminoglycosides have been of historical significance in genetics and microbiology. For example, mutations to streptomycin resistance were employed as counterselective genetic markers in the historic experiments of William Hayes that demonstrated the existence of bacterial conjugation and the requirement of donor (Hfr or F-b) and receptor (F—) species. ... 

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. 

The stability of the /3-barrel itself was demonstrated in engineering experiments with OmpA. The four external loops of OmpA were replaced by shortcuts in all possible combinations (Koebnik, 1999). The resulting deletion mutants lost their biological functions in bacterial / -conjugation and as bacteriophage receptors, but kept the transmembrane /1-barrel as demonstrated by their resistance to proteolysis and thermal denaturation. The results confirm the expectation that the large external loops do not contribute to /1-barrel folding and stability. 

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... 

A second way in which bacterial cells can acquire drug resistance is by gaining that resistance from another bacterial cell. This occurs because it is possible for genetic information to be passed on directly from one bacterial cell to another. There are two main methods by which this can take place—transduction and conjugation. 

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