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Transposition of gentamicin resistance to staphylococcal plasmids encoding resistance to cationic agents
Abstract:
Plasmid pWG115 isolated from a methicillin-resistant Staphylococcus aureus encodes resistance to cationic surface-active agents and trimethoprim. It has a molecular weight of ca 14.6 megadaltons and can be transferred to other strains of staphylococci in mixed-culture transfer with propamidine isethionate as a selective agent. Gentamicin resistance in Australian methicillin-resistant Staph. aureus isolates can be either chromosomal or plasmid-borne. The most common gentamicin resistance plasmid is 18.0 megadaltons and also encodes resistance to trimethoprim and cationic surface-active agents. This suggested that pWG115 was related to gentamicin resistance plasmids and that it may provide a target for the postulated gentamicin resistance transposon. This paper demonstrates that the chromosomal gentamicin resistance determinant from WG523 can transpose into pWG115 to generate an 18.0 megadalton plasmid, phenotypically indistinguishable from the naturally occurring gentamicin resistance plasmids such as pWG53. EcoR1 restriction enzyme analysis demonstrated that gentamicin resistance can transpose into at least two sites on pWG115. One of these sites generates EcoR1 restriction fragments identical to pWG53. The 5.2 kilobase pair (3.4 megadalton) element involved confers low-level resistance to gentamicin, cross resistance to tobramycin and kanamycin, and has been designated Tn3851.
Insights
Researchers demonstrated that a chromosomal gentamicin resistance gene can integrate into the pWG115 plasmid in methicillin-resistant Staphylococcus aureus. This integration creates a new plasmid, Tn3851, which confers resistance to multiple antibiotics.
Area of Science:
- Microbiology
- Molecular Biology
- Genetics
Background:
- Methicillin-resistant Staphylococcus aureus (MRSA) poses a significant public health threat.
- Antibiotic resistance in MRSA is often mediated by plasmids and transposons.
- Plasmid pWG115 confers resistance to trimethoprim and cationic surface-active agents.
Purpose of the Study:
- To investigate the relationship between pWG115 and gentamicin resistance plasmids.
- To determine if chromosomal gentamicin resistance determinants can transpose into pWG115.
- To characterize the resulting plasmid and its antibiotic resistance profile.
Main Methods:
- Mixed-culture transfer experiments using selective agents.
- EcoR1 restriction enzyme analysis of plasmids.
- Phenotypic characterization of antibiotic resistance.
Main Results:
- Chromosomal gentamicin resistance determinant successfully transposed into pWG115.
- An 18.0 megadalton plasmid, phenotypically identical to naturally occurring gentamicin resistance plasmids, was generated.
- EcoR1 analysis revealed transposition into at least two sites on pWG115, with one site matching pWG53.
- The transposed element, designated Tn3851, confers resistance to gentamicin, tobramycin, and kanamycin.
Conclusions:
- The chromosomal gentamicin resistance determinant can transpose into pWG115, forming a novel plasmid.
- This transposition mechanism contributes to the dissemination of antibiotic resistance in MRSA.
- The identified transposon, Tn3851, is a significant factor in multi-drug resistance in Staphylococcus aureus.