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Novel mechanism for plasmid-mediated erythromycin resistance by pNE24 from Staphylococcus epidermidis
Abstract:
We describe an unusual type of erythromycin resistance (Emr) mediated by a plasmid designated pNE24 from Staphylococcus epidermidis. This 26.5-kilobase plasmid encodes resistance strictly to 14-membered macrolide antibiotics, erythromycin, and oleandomycin. Resistance to other macrolide-lincosamide-streptogramin B (MLS) antibiotics was not observed even after a prior induction stimulus with various MLS antibiotics. Plasmid pNE24 was found to express resistance constitutively and manifested a low to intermediate MIC (62.5 micrograms/ml) for erythromycin. The resistance gene, designated erpA, appears to mediate resistance by altering the permeability of the host cell for erythromycin, because the measured uptake of 14C-labeled erythromycin by strain 958-2 (containing pNE24) was lower than for the erythromycin-susceptible, isogenic strain 958-1. No inactivation of erythromycin in overnight broth culture supernatants could be detected. In addition, no significant loss in binding affinity between [14C]erythromycin and ribosome could be detected for ribosomes isolated from strain 958-2 relative to 958-1, indicating that pNE24 probably does not produce a modification of the bacterial ribosome. No other selectable marker was found associated with pNE24; however, a 60,000-dalton protein was present only in the membrane fractions of cells (958-2) containing pNE24 and may play a role in mediating resistance to erythromycin.
Insights
A novel plasmid, pNE24, from Staphylococcus epidermidis confers erythromycin resistance (Emr) by reducing drug uptake. This plasmid-mediated resistance mechanism does not involve drug inactivation or ribosomal modification.
Area of Science:
- Microbiology
- Molecular Biology
- Genetics
Background:
- Erythromycin resistance (Emr) is a growing concern in Staphylococcus epidermidis infections.
- Mechanisms of Emr often involve drug inactivation, target modification, or active efflux.
- Understanding novel resistance mechanisms is crucial for developing effective treatments.
Purpose of the Study:
- To characterize a newly identified plasmid, pNE24, mediating erythromycin resistance in Staphylococcus epidermidis.
- To elucidate the mechanism by which pNE24 confers resistance to erythromycin.
Main Methods:
- Plasmid isolation and characterization (pNE24, 26.5 kb).
- Determination of minimum inhibitory concentrations (MICs) for various macrolide-lincosamide-streptogramin B (MLS) antibiotics.
- Measurement of 14C-labeled erythromycin uptake in resistant and susceptible strains.
- Analysis of erythromycin inactivation and ribosome binding affinity.
Main Results:
- Plasmid pNE24 confers constitutive, low-to-intermediate level resistance specifically to erythromycin and oleandomycin.
- Reduced uptake of erythromycin in pNE24-containing cells suggests a permeability alteration.
- No evidence of erythromycin inactivation or significant alteration in ribosome binding was observed.
- A 60,000-dalton membrane protein, potentially involved in resistance, was identified.
Conclusions:
- Plasmid pNE24 mediates erythromycin resistance through a mechanism involving decreased drug permeability.
- This resistance is not due to drug inactivation or ribosomal modification.
- The identified membrane protein may play a role in this novel resistance pathway.