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J. Bacteriol., 09 1997, 5947-5950, Vol 179, No. 18
EC Becker and RJ Meyer
R1162 is a representative member of the broad-host-range IncQ group of
multicopy plasmids. Lower-copy-number derivatives of R1162 were constructed
in vitro and shown to be unstable, indicating that partitioning of plasmid
copies at cell division is due to random distribution and not to an active
partitioning mechanism. However, the normal copy number of R1162 reduces
cell fitness during growth in broth and favors the emergence of unstable,
lower-copy-number variants. As a result, plasmid-borne antibiotic
resistance genes active at a low copy number eventually result in plasmid
loss during periods of no selection. We argue that the maintenance of R1162
in a population requires a gene that is selected only at high levels. This
reduces the potential for acquiring genes from other R factors and could
explain the limited variety of antibiotic resistance genes contained by
naturally occurring IncQ plasmids.
Copyright © 1997, American Society for Microbiology
Acquisition of resistance genes by the IncQ plasmid R1162 is limited by its high copy number and lack of a partitioning mechanism
Department of Microbiology, University of Texas, Austin 78712, USA.
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