title: Bacterial plasmids--an overview.
abstract: Resistance to antimicrobial substances and various factors contributing to pathogenicity are only some of the bacterial traits that can be determined by plasmid genes. Not all plasmids are involved with resistance, nor is all resistance to antimicrobials plasmid-mediated. Nevertheless, the impact of R-plasmids on the choice of antimicrobial therapy is substantial, especially in hospital and when dealing with certain community pathogens, such as Haemophilus influenzae. The discovery of transposition elements has helped us to understand the rapidity with which certain resistance determinants develop and become disseminated among diverse microbial species. Similarly, not all determinants of microbial pathogenicity are plasmid encoded and the genes for many toxins, cellular attachment pili, iron sequestration systems, etc. are found on the bacterial chromosomes. In Yersinia, pathogenicity is even more complex in that plasmid determinants play an essential role, but only in concert with chromosomal genes. The particularly significant features of such pathogenicity-determined plasmid-mediated genes is not that they are found on extrachromosomal elements, but that they may possess greater genetic mobility. Another consequence of the presence of virulence genes on bacterial plasmids is that it makes them easier to study by the newer techniques of microbial genetics and molecular biology.
mesh_terms: D000900:Anti-Bacterial Agents / Q000494:pharmacology; D001427:Bacterial Toxins / Q000235:genetics; D002965:Classification; D004352:Drug Resistance, Microbial; D004926:Escherichia coli / Q000235:genetics*; D006801:Humans; D010957:Plasmids
chemical_list: D000900:Anti-Bacterial Agents; D001427:Bacterial Toxins