infectious diseases
Overview of Antibacterial Drugs
Antibiotic Resistance
Resistance to an antibiotic may be inherent in a particular bacterial species or may be acquired through mutations or acquisition of genes for antibiotic resistance that are obtained from another organism. Different mechanisms for resistance are encoded by these genes (see table Common Mechanisms of Antibiotic Resistance ). Resistance genes can be transmitted between 2 bacterial cells by the following mechanisms: Transformation (uptake of naked DNA from another organism) Transduction (infection by a bacteriophage) Conjugation (exchange of genetic material in the form of either plasmids, which are pieces of independently replicating extrachromosomal DNA, or transposons, which are movable pieces of chromosomal DNA) Plasmids and transposons can rapidly disseminate resistance genes. Antibiotic use preferentially eliminates nonresistant bacteria, increasing the proportion of resistant bacteria that remain. Antibiotic use has this effect not only on pathogenic bacteria but also on normal microbiota; resistant normal microbiota can become a reservoir for resistance genes that can spread to pathogens. 