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Multiple copies of IS256 in staphylococci
K G Dyke1, S Aubert, N el Solh
1National Reference Center for Staphylococci, Institut Pasteur, Paris, France.
Abstract:
EcoRI-digested cellular DNAs of 150 staphylococcal clinical isolates were probed with a plasmid containing a DNA piece from within the open reading frame of IS256. Most of the Gmr staphylococcal isolates tested contained more copies of IS256 than those associated with Tn4001 carried by these isolates. Three distinct copies of IS256 together with their flanking DNA were isolated by cloning from an EcoRI digest of the cellular DNA of the Gmr isolate, BM3121. These three copies of IS256 were shown to be intact. The results from DNA sequencing revealed that one of the three copies is flanked by 8-bp direct repeats, and it is suggested that this may be the result of insertion of the IS256 at this site by autonomous movement of the IS element. The insert DNA of all three clones hybridized to the cellular DNA prepared from a Staphylococcus aureus strain that carries neither IS256 nor the aacA-aphD gene. Two of the clones hybridized to several EcoRI fragments of the cellular DNA of this strain, indicating that in these cases IS256 is flanked by DNA present as several copies on the chromosome.
Insights
Most staphylococcal clinical isolates contain multiple copies of the insertion sequence IS256. Researchers identified intact IS256 copies, with one potentially inserted via autonomous movement, suggesting widespread genomic presence.
Area of Science:
- Microbiology
- Genetics
- Molecular Biology
Background:
- The insertion sequence IS256 is found in staphylococci, often associated with antibiotic resistance genes like aacA-aphD.
- Understanding the distribution and mobility of IS256 is crucial for tracking its role in bacterial evolution and antibiotic resistance.
Purpose of the Study:
- To investigate the copy number and genomic context of IS256 in staphylococcal clinical isolates.
- To characterize the flanking DNA of IS256 elements to understand their insertion mechanisms.
Main Methods:
- Probing EcoRI-digested staphylococcal DNA with an IS256-containing plasmid.
- Cloning and DNA sequencing of IS256 copies and their flanking regions.
- Hybridization experiments to analyze IS256 distribution in different strains.
Main Results:
- Most tested staphylococcal isolates harbored more IS256 copies than those linked to Tn4001.
- Three intact IS256 copies with flanking DNA were isolated from a Gmr isolate.
- One IS256 copy was flanked by 8-bp direct repeats, suggesting autonomous insertion.
- IS256 elements were found integrated into chromosomal DNA, sometimes adjacent to multi-copy regions.
Conclusions:
- IS256 is present in multiple copies in many staphylococcal clinical isolates.
- Evidence suggests IS256 can move autonomously, inserting into the genome.
- The flanking DNA of IS256 provides insights into its integration and potential role in genomic rearrangements.