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Analysis of two Staphylococcus epidermidis plasmids coding for resistance to streptogramin A
1Unité des Staphylocoques, Centre National de Référence des Staphylocoques, Paris Cedex 15, 75724, France.
Abstract:
The two Staphylococcus epidermidis plasmids pIP1629 (7.5 kb) and pIP1630 (14.4 kb) contain the vga gene conferring resistance to streptogramin A. All the sequences of pIP1629, except two of the four 22-nt iterons preceding the replication gene, were found in pIP1630. The additional 6.9-kb fragment of pIP1630 is similar to the mobilizable S. epidermidis plasmid pSK639, carrying the dfrA-thyE-orf140 operon and thought to replicate by an iteron controlled theta-type replication mechanism. The replication-mobilization elements of pIP1629 and pSK639 are very similar despite having been isolated in France and in Australia, respectively, showing that they are geographically widely dispersed in S. epidermidis. The gene thyE encoding thymidylate synthetase carried by pSK639 is not present in pIP1630. pIP1630 probably arose by the recombination of two homologous plasmids carrying distinct resistance determinants.
Insights
Two Staphylococcus epidermidis plasmids, pIP1629 and pIP1630, carry the streptogramin A resistance gene (vga). Plasmid pIP1630 likely formed from recombination of two distinct resistance-carrying plasmids.
Area of Science:
- Microbiology
- Molecular Biology
- Genetics
Background:
- Staphylococcus epidermidis is a common cause of nosocomial infections.
- Plasmids are extrachromosomal DNA elements that can carry antibiotic resistance genes.
- The vga gene confers resistance to streptogramin A antibiotics.
Purpose of the Study:
- To characterize the genetic makeup of two S. epidermidis plasmids, pIP1629 and pIP1630.
- To investigate the origins and dissemination of these plasmids within S. epidermidis populations.
Main Methods:
- DNA sequencing and comparative analysis of plasmids pIP1629, pIP1630, and pSK639.
- Identification of shared and unique genetic elements, including resistance genes and replication mechanisms.
Main Results:
- Both pIP1629 and pIP1630 contain the vga gene for streptogramin A resistance.
- pIP1630 shares significant sequence homology with pIP1629 and the mobilizable plasmid pSK639.
- Replication-mobilization elements of pIP1629 and pSK639 are highly similar, indicating wide geographic dispersal.
Conclusions:
- Plasmid pIP1630 likely resulted from the recombination of two ancestral plasmids, each carrying different resistance determinants.
- The widespread distribution of similar replication-mobilization elements suggests efficient plasmid transfer and maintenance in S. epidermidis.