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Genetic study of plasmid-associated zonal resistance to lincomycin in Streptococcus pyogenes
Abstract:
The phenomenon of zonal resistance to lincomycin, which is characteristic of most clinical isolates with lincomycin resistance in Streptococcus pyogenes, has been studied. These strains grow within a defined concentration range of lincomycin (approximately 60 to 200 microgram/ml), or at lincomycin concentrations below the minimal inhibitory concentration for susceptible strains. It is shown that the zonal growth phenomenon is a stable phenotype and results from induction of resistance only within the zonal concentration range of lincomycin. These strains also possess inducible resistance to erythromycin which is nonzonal in character. One-step mutations to constitutive resistance have been isolated which are of two types: constitutive for lincomycin or for erythromycin, but not for both. Those strains with constitutive erythromycin resistance retain their zonal resistance for lincomycin. Mutants doubly constitutive for both lincomycin and erythromycin can be obtained by a second mutational step from either of the singly constitutive mutants. Satellite deoxyribonucleic acid has been shown to be present in the zonal resistant strains. A plasmid, pSM10419, of 14.9 megadaltons, has been isolated from one of the doubly constitutive mutants and used to jointly transform Streptococcus sanguis strain Challis to constitutive resistance to both lincomycin and erythromycin. From this, a multicopy plasmid of reduced size, pSM10 (5.4 megadaltons), which retains its resistance phenotype, has been isolated and mapped with restriction endonucleases HindIII (three sites), EcoRI (one site), KpnI (one site), and HpaI (one site). The staphylococcal plasmid pC221 (2.9 megadaltons; chloramphenicol resistant) has been fused to pSM10 at the EcoRI site resulting in a chimeric plasmid, pSM10221 (8.3 megadaltons), which retains resistance to chloramphenicol, erythromycin, and lincomycin. pSM10 is therefore suggestive as an effective cloning vehicle for the genus Streptococcus.
Insights
Zonal resistance in Streptococcus pyogenes is a stable, inducible trait. Researchers isolated plasmids, including pSM10, demonstrating potential as a Streptococcus cloning vehicle for antibiotic resistance studies.
Area of Science:
- Microbiology
- Molecular Biology
- Genetics
Background:
- Most clinical isolates of Streptococcus pyogenes exhibit zonal resistance to lincomycin.
- This resistance allows growth within a specific concentration range of lincomycin, below the minimal inhibitory concentration for susceptible strains.
Purpose of the Study:
- To investigate the stable phenotype of zonal resistance to lincomycin in Streptococcus pyogenes.
- To characterize the genetic basis of inducible and constitutive resistance to lincomycin and erythromycin.
- To explore the potential of isolated plasmids as cloning vectors in Streptococcus.
Main Methods:
- Phenotypic characterization of zonal and nonzonal resistance.
- Isolation and characterization of one-step and two-step mutants for constitutive resistance.
- Isolation and manipulation of plasmids (pSM10419, pSM10, pSM10221) using restriction endonuclease mapping.
- Transformation experiments using Streptococcus sanguis strain Challis.
Main Results:
- Zonal resistance to lincomycin is a stable, inducible phenotype.
- Inducible resistance to erythromycin is nonzonal.
- Mutants constitutive for lincomycin or erythromycin resistance were isolated; constitutive erythromycin resistance retained lincomycin zonal resistance.
- Satellite DNA was present in zonal resistant strains.
- Plasmid pSM10 (5.4 megadaltons) was isolated and mapped, showing potential as a Streptococcus cloning vehicle.
- Chimeric plasmid pSM10221 (8.3 megadaltons) conferred resistance to chloramphenicol, erythromycin, and lincomycin.
Conclusions:
- Zonal resistance in Streptococcus pyogenes is a stable, inducible trait.
- Plasmid pSM10 is a promising cloning vehicle for the genus Streptococcus.
- Understanding these resistance mechanisms and plasmids aids in developing strategies against antibiotic resistance.