[Mechanism of acquiring drug-resistance genes in pathogenic bacteria]

Pathogenic bacteria acquire resistance to chemotherapeutic agents by mutational events in the intrinsic genes or by incorporating foreign resistance genes. The resistance genes to various drugs were transferred among bacteria by transformation with free DNA, phage-mediated transduction, or cell to cell conjugation. Plasmids are capable of self-replication and self-transfer by conjugation. Drug-resistance genes are incorporated into plasmids by transposable elements, transposons. Several kinds of transposons carrying resistance genes to various drugs, or some transposons carrying multiresistance genes, are mobile among genetic elements and confer multiresistance on pathogenic bacteria. There is a specific element, integron, on transposons or plasmids. The integron has the gene and the site for incorporating resistance genes as cassettes and allows expression of the genes.