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Identification of a Staphylococcus aureus transposon (Tn4291) that carries the methicillin resistance gene(s)
1Division of Biology, Kansas State University, Manhattan 66506.
Abstract:
We isolated a transposon (Tn4291) that carries the resistance gene(s) for methicillin in a secondary insertion site on the penicillinase plasmid pI524. Transposition of Tn4291 into pI524 occurred during the transduction of the tetracycline resistance plasmid pSN1 from a methicillin-resistant donor into a recipient that carried the mec allele in the primary site on the chromosome. Insertion of Tn4291 caused extensive rearrangement of pI524 and resulted in the formation of a 27.9-kilobase-pair plasmid (pIT103) which coded for resistance to methicillin and cadmium, but not penicillin. Although resistance to methicillin and cadmium were always linked, Tn4291 was stably maintained only in the presence of a chromosomal mec allele, while in its absence the plasmid was unstable and transposition to the primary site occurred. Subsequently, a 20.1-kilobase-pair plasmid, pIT203, was formed which retained cadmium resistance and regained the ability to express beta-lactamase activity.
Insights
A novel transposon, Tn4291, carrying methicillin resistance genes was identified. Its stable maintenance requires a chromosomal mec allele, influencing plasmid stability and rearrangement.
Area of Science:
- Microbiology
- Molecular Biology
- Genetics
Background:
- Methicillin resistance is a significant clinical concern.
- Understanding the genetic elements and mechanisms of resistance spread is crucial.
Purpose of the Study:
- To characterize a transposon (Tn4291) involved in methicillin resistance.
- To investigate the transposition dynamics and plasmid stability associated with Tn4291.
Main Methods:
- Isolation and characterization of transposon Tn4291.
- Plasmid analysis and manipulation through transduction.
- Assessment of antibiotic resistance profiles and plasmid stability.
Main Results:
- Tn4291 was identified on the penicillinase plasmid pI524, causing its rearrangement into pIT103.
- pIT103 conferred resistance to methicillin and cadmium, with stable maintenance dependent on a chromosomal mec allele.
- Plasmid instability and secondary transposition occurred in the absence of the chromosomal mec allele, leading to pIT203 formation.
Conclusions:
- Tn4291 plays a role in the dissemination of methicillin resistance.
- Chromosomal mec allele presence is essential for the stability of Tn4291-carrying plasmids.
- Transposition events can lead to significant plasmid alterations and acquisition of new resistance traits.