Evolution of bacterial resistance to antibiotics

Bacterial resistance to antibiotics is often plasmid-mediated and the associated genes encoded by transposable elements. These elements play a central role in evolution by providing mechanisms for the generation of diversity and, in conjuntion with DNA transfer systems, for the dissemination of resistance to other bacteria. Resistance to antibiotics in gram-negative bacilli is most commonly mediated by R plasmids and by genes carried by transposons and integrons. In gram-positive cocci the conjugative transposons are fundamental for antibiotic resistance. Acquired multiple R in S. pneumoniae can result from the presence of transposon Tn1545, which carries determinants erm (B), tet (M), aph(3')-III, and catpC194.