Plasmids and the Virulence of Enteric and Other Bacterial Pathogens

Excerpt

Bacterial plasmids are extrachromosomal, circular, double-stranded DNA, genetic accessory elements that have been found to encode many important properties in more than 50 different bacterial genera. For example, these genetic units can mediate conjugal DNA transfer, resistance to many antibiotics and divalent cations, degradation of organic compounds (such as napthalene or hexachlorophene), and some key diagnostic biochemical properties (such as urease or hydrogen sulfide production or lactose utilization). Plasmids generally range in size from about 5000 to 450 000 nucleotide base pairs—that is, each plasmid can potentially encode from 5 to more than 400 average-sized accessory proteins. Moreover, a single