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Plasmid DNA content of multiresistant Staphylococcus aureus strains
Abstract:
Multiresistant S. aureus strains (also called methicillin-resistant in clinical laboratories) share many common properties. In addition to the commonly used epidemiological markers (pattern of resistance to antibiotics and metal ions, serotype and lysotype), we considered using the molecular and genetical properties of the plasmid DNA harboured by these strains. In this paper we report an epidemiological study of two groups of S. aureus strains sampled since 1975 and carrying new resistance characters which appeared with increasing frequency in France. The Tm-SgR strains (5 strains) carry, in addition to 13 resistance characters commonly observed, two new characters: the resistance to gramin components A and B (Sg). The two new characters were shown to be encoded by a single plasmid. Amongst the 5 strains studied, two harbour a similar plasmid DNA content while the three others were clearly distinct. Because of the variability of the plasmid DNA content observed in these strains, the similarity of this content observed between two of them suggest a close phylogenic relationship. These two strains are probably derivatives from a single clone. The spread of the two new characters amongst the distinct strains might be related to the spread of ancestrally related Tm-Sg plasmids. The Tob-GenR strains (16 strains) carry, in addition to 12 wide-spread resistance markers, the newly observed resistance to many aminoglycosides, mainly the resistance to tobramycin (Tob) and gentamicin (Gen). They all harbour a 22-kb plasmid DNA generating similar restriction cleavage patterns and conferring the resistance to penicillin G, arsenate, arsenite and cadmium. Some of them harbour one or two extra small plasmids (3.4 and 2.3 kb); the presence of these two plasmids was not associated with a modification of the resistance pattern of the strains. Most of the resistance characters--including the new ones--are probably encoded by chromosomal genes. In this epidemiological situation, the spread of the new aminoglycoside resistance characters carried by the 16 strains having the same phenotype and harbouring the same 22-kb plasmid is attributed to the spread of derivatives from a single clone.
Insights
This study investigated multiresistant Staphylococcus aureus strains in France. Researchers found that new antibiotic resistance traits in these strains are often linked to specific plasmid DNA, suggesting clonal spread and potential phylogenetic relationships.
Area of Science:
- Microbiology
- Epidemiology
- Molecular Genetics
Background:
- Multiresistant Staphylococcus aureus, including methicillin-resistant strains, exhibit diverse resistance patterns.
- Traditional epidemiological markers like antibiotic resistance and serotyping are often used.
- Molecular and genetic properties of plasmid DNA offer additional insights into strain relationships.
Purpose of the Study:
- To conduct an epidemiological study of two groups of S. aureus strains in France.
- To investigate the role of plasmid DNA in the spread of new resistance characters.
- To explore potential phylogenetic relationships among strains based on plasmid content.
Main Methods:
- Analysis of resistance patterns to antibiotics and metal ions.
- Characterization of plasmid DNA content and restriction cleavage patterns.
- Epidemiological sampling of S. aureus strains since 1975.
Main Results:
- Tm-SgR strains showed resistance to gramin components A and B (Sg), encoded by a single plasmid, with some strains suggesting clonal origin.
- Tob-GenR strains exhibited resistance to aminoglycosides like tobramycin (Tob) and gentamicin (Gen), linked to a 22-kb plasmid.
- Most resistance characters, including new ones, are likely encoded by chromosomal genes, but plasmid spread is implicated in specific resistance traits.
Conclusions:
- Plasmid DNA content can indicate close phylogenetic relationships and clonal spread among S. aureus strains.
- The spread of novel resistance characters, such as Sg and aminoglycoside resistance, may be associated with the dissemination of specific ancestral plasmids or clones.
- Understanding the genetic basis and epidemiological spread of resistance is crucial for controlling multiresistant bacteria.