Genome of a Plasmid from a Multiresistant Corynebacterium

Plasmids are double-stranded circular DNA
molecules in bacteria but separate from the
bacterial chromosome. They are self-replicating
and occur in a symbiotic or parasitic relationship
with the host cell. The number of plasmids
per bacterial cell varies from a few to thousands.
Their sizes range from a few thousand
base pairs to more than 100 kb. Plasmids usually
confer a benefit to the host cell, often because
they contain genes encoding enzymes
that inactivate antibiotics. Drug-resistant
plasmids pose amajor threat to successful antibiotic
therapy. Since many plasmids also contain
transfer genes encoding proteins that form
amacromolecular tube, or pilus, through which
a copy of plasmid DNA can be transferred to
other bacteria, antibiotic resistance can spread
very rapidly. The following example provides
new insights into the origin and evolution of a
multiresistant plasmid composed of DNA segments
derived from bacteria of very different
origins (soil bacteria and plant, animal, and
human pathogens).