IS257 and heterogeneous location of ileS2 gene in high-level mupirocin resistance staphylococcal plasmids

Abstract number: P2042

Pérez Roth E., Alcoba Florez J., Laich F., Méndez Álvarez S.

Objectives: High-level mupirocin resistance (Hi-Mupr) in S. aureus is associated with an additional isoleucyl-tRNA synthetase that is encoded by the ileS2 gene. We have previously reported that the ileS2 was carried on 9 conjugative plasmids belonging to 4 structural groups (i.e. S1 to S4) and that the location of ileS2 varied between groups. Different sizes of ileS2-hybridising HindIII plasmid fragments permitted 5 polymorphs of the ileS2 locus to be distinguished. In pUSA03 and pGO400 Hi-Mupr plasmids the ileS2 gene has been found to be flanked by 2 directly repeated copies of IS257. In this work we analysed the basis of the heterogeneous location of the ileS2 gene.

Methods: The study attempted to detect the existence of IS257 flanking the ileS2 gene, and to amplify the spacer regions between the upstream (IS-L) and downstream (IS-R) copies of IS257 and ileS2 from each of the 9 Hi-Mupr plasmids. Spacer regions confirmation was done by hybridisation with 2 probes for the ileS2 and an IS257 internal probe.

Results: IS-L and IS-R copies of IS257 were present in all 9 Hi-Mupr plasmids. The copy of the IS-L was detected in either orientation and the sizes of the spacer regions (with IS257 in either orientation) vary. Heterogeneity was also observed downstream to ileS2. Plasmids of the same group showed an identical organisation of IS257-ileS2 spacer regions. The IS-L copies in plasmids belonging to S1 and S2 groups (i.e. ISpS1-L, ISpS2-L) are in the same orientation as ileS2. On the other hand, in S3 and S4 plasmids the IS-L copies (i.e. ISpS3-L, ISpS4-L) are in the reverse orientation. ISpS1-R, ISpS2-R and ISpS3-R are in the same orientation as ileS2, contrary to the case of ISpS4-R. Considering both sides, different groups have distinct IS257-ileS2 organisations. As in pUSA03 and pGO400, plasmids belonging to S1 and S2 groups showed directly repeated copies of IS257 but upstream IS257-ileS2 amplifications differed in size. S3 group plasmids have inverted copies of IS257, while in plasmids belonging to S4 group, both copies were in opposite orientation to ileS2.

Conclusion: The results support the hypothesis that IS257-mediated events are responsible for the variable location of the ileS2 gene in Hi-Mupr plasmids. The IS257-ileS2 spacer regions heterogeneity could potentially be used as an epidemiological tool for monitoring Hi-Mupr plasmid dissemination. The molecular basis for the heterogeneity observed requires additional detailed characterisation.

Session Details

Date: 19/04/2008
Time: 00:00-00:00
Session name: 18th European Congress of Clinical Microbiology and Infectious Diseases
Location: Barcelona, Spain
Presentation type:
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