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Molecular analysis of a mobilizable theta-mode trimethoprim resistance plasmid from coagulase-negative staphylococci
S Apisiridej1, A Leelaporn, C D Scaramuzzi
1School of Biological Sciences, University of Sydney, Sydney, New South Wales, 2006, Australia.
Abstract:
The Staphylococcus epidermidis plasmid pSK639 is the prototype of a newly described family of small plasmids identified in clinical staphylococcal isolates. pSK639 is 8 kb in length and possesses a composite structure consisting of an IS257-flanked segment mediating trimethoprim resistance (Tpr), and regions responsible for replication and mobilization of the plasmid. Comparative sequence analysis suggests that a pSK639-like plasmid may represent a progenitor of previously identified staphylococcal Tpr determinants related to the transposon-like structure, Tn4003. In contrast to the small staphylococcal plasmids characterized to date that all utilize a rolling circle mode of replication, the replication region of pSK639 was found to contain features typical of an iteron-controlled theta-mode replicon. pSK639 is the first small plasmid of this type to be identified in the staphylococci.
Insights
The novel Staphylococcus epidermidis plasmid pSK639, a new family prototype, exhibits unique theta-mode replication, unlike other small staphylococcal plasmids. This finding offers insights into trimethoprim resistance gene evolution in staphylococci.
Area of Science:
- Microbiology
- Molecular Biology
- Genetics
Background:
- Staphylococcus epidermidis is a common cause of nosocomial infections.
- Small plasmids are frequently found in staphylococcal clinical isolates.
- Trimethoprim resistance is a significant concern in treating staphylococcal infections.
Purpose of the Study:
- To characterize the novel Staphylococcus epidermidis plasmid pSK639.
- To investigate the replication mechanism of pSK639.
- To explore the evolutionary relationship of pSK639 with other staphylococcal resistance determinants.
Main Methods:
- Plasmid DNA isolation and sequencing.
- Comparative sequence analysis.
- Bioinformatic analysis of replication and mobilization regions.
Main Results:
- pSK639 is an 8 kb composite plasmid carrying a trimethoprim resistance (Tpr) determinant.
- It possesses a unique iteron-controlled theta-mode replication region, distinct from rolling circle replication seen in other small staphylococcal plasmids.
- Sequence analysis suggests pSK639-like plasmids may be progenitors of Tn4003-related Tpr determinants.
Conclusions:
- pSK639 represents a novel type of small plasmid in staphylococci, utilizing theta-mode replication.
- This discovery provides a new model for understanding plasmid replication and the evolution of trimethoprim resistance in staphylococci.
- pSK639 offers insights into the genetic mechanisms underlying antibiotic resistance in clinical staphylococcal isolates.