Plasmids in epidermolytic strains of Staphylococcus aureus
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Abstract:
Thirty-four epidermolytic toxin-producing strains of Staphylococcus aureus obtained from a variety of sources were screened for the presence of plasmid DNA. All serotype ii toxin producers harboured a large 42 kilobase pairs (kb) plasmid. Elimination of these plasmids resulted in the simultaneous loss of a bacteriocin determinant (Bac+) and type ii toxin production (Toxii+). Some strains producing serotype i toxin (Toxi+) contained similar 42 kb plasmids. Elimination of these plasmids resulted in the loss of only bacteriocin production. Strains producing both toxin serotypes readily lost Toxii+ and Bac+, which were carried on the same plasmid, but Toxi+ could not be eliminated. Thus Toxi+ was probably chromosomally determined, while Toxii+ was a plasmid-encoded marker. In some strains cadmium resistance was also linked to the 42 kb plasmid. The 42 kb plasmids from seven strains with different phenotypes were analysed with restriction endonucleases EcoRI and HindIII. The plasmids shared 19 of 22 HindIII fragments indicating that they are closely related to each other.
Insights
Staphylococcus aureus plasmids carrying toxin genes were identified. Plasmid elimination revealed type ii toxin and bacteriocin production are plasmid-encoded, while type i toxin is likely chromosomal.
Area of Science:
- Microbiology
- Molecular Biology
- Genetics
Background:
- Staphylococcus aureus produces various toxins, including epidermolytic toxins (serotypes i and ii).
- The genetic basis for toxin production, particularly plasmid involvement, requires further elucidation.
- Bacteriocin production and antibiotic resistance can also be plasmid-mediated in bacteria.
Purpose of the Study:
- To investigate the role of plasmid DNA in the production of Staphylococcus aureus epidermolytic toxins (serotypes i and ii).
- To determine the genetic linkage between toxin production, bacteriocin production, and cadmium resistance.
- To analyze the relatedness of plasmids carrying these determinants.
Main Methods:
- Screening of Staphylococcus aureus strains for plasmid DNA using gel electrophoresis.
- Plasmid elimination through curing techniques.
- Phenotypic analysis of cured strains for toxin and bacteriocin production.
- Restriction endonuclease analysis (EcoRI and HindIII) of isolated plasmids.
Main Results:
- All serotype ii toxin-producing strains harbored a 42 kb plasmid, essential for both type ii toxin (Toxii+) and bacteriocin (Bac+) production.
- Serotype i toxin (Toxi+) production was not consistently eliminated with plasmid loss, suggesting chromosomal linkage.
- Cadmium resistance was linked to the 42 kb plasmid in some strains.
- Restriction analysis indicated close relatedness among the 42 kb plasmids from different strains.
Conclusions:
- Type ii toxin and bacteriocin production in Staphylococcus aureus are plasmid-encoded.
- Type i toxin production is likely chromosomally determined.
- The 42 kb plasmid plays a significant role in mediating multiple phenotypes, including toxin and bacteriocin production and potentially cadmium resistance.