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Naturally occurring Staphylococcus epidermidis plasmid expressing constitutive macrolide-lincosamide-streptogramin B
Abstract:
A naturally occurring constitutive macrolide-lincosamide-streptogramin B (MLS) resistance plasmid, pNE131, from Staphylococcus epidermidis was chosen to study the molecular basis of constitutive expression. Restriction and functional maps of pNE131 are presented along with the nucleotide sequence of ermM, the gene which mediates constitutive MLS resistance. Sharing 98% sequence homology within the 870-base-pair Sau3A-TaqI fragment, ermM appears to be almost identical to ermC, the inducible MLS resistance determinant from S. aureus (pE194). The two genes share nearly identical sequences, except in the 5' promoter region of ermM. Constitutive expression of ermM is due to the deletion of 107 base pairs relative to ermC; the deletion removes critical sequences for attenuation, resulting in constitutive methylase expression.
Insights
This study reveals the molecular basis for constitutive macrolide-lincosamide-streptogramin B (MLS) resistance in Staphylococcus epidermidis. A specific deletion in the ermM gene explains its continuous expression, unlike inducible resistance.
Area of Science:
- Microbiology
- Molecular Biology
- Genetics
Background:
- Macrolide-lincosamide-streptogramin B (MLS) resistance is a significant challenge in bacterial infections.
- Constitutive expression of resistance genes, unlike inducible expression, leads to continuous antibiotic resistance.
- The plasmid pNE131 from Staphylococcus epidermidis carries a gene mediating constitutive MLS resistance.
Purpose of the Study:
- To investigate the molecular mechanisms underlying the constitutive expression of MLS resistance.
- To characterize the ermM gene responsible for constitutive MLS resistance in pNE131.
- To compare the ermM gene with the inducible ermC gene.
Main Methods:
- Restriction and functional mapping of the pNE131 plasmid.
- Nucleotide sequencing of the ermM gene.
- Sequence comparison between ermM and ermC genes.
Main Results:
- The ermM gene, responsible for constitutive MLS resistance, was sequenced.
- ermM shares 98% sequence homology with ermC, the inducible MLS resistance determinant.
- A 107-base-pair deletion in the 5' promoter region of ermM, compared to ermC, was identified as the cause of constitutive expression.
Conclusions:
- Constitutive MLS resistance mediated by ermM is due to a specific deletion in its promoter region.
- This deletion in ermM removes sequences critical for attenuation, leading to continuous methylase expression and resistance.
- Understanding these mechanisms is crucial for combating antibiotic resistance.