In-vitro characteristics of glycopeptide resistant strains of Staphylococcus epidermidis isolated from patients on CAPD

Area of Science:

• Microbiology
• Antibiotic Resistance
• Molecular Biology

Background:

• Glycopeptide antibiotics like vancomycin and teicoplanin are crucial for treating Gram-positive bacterial infections.
• Emergence of antibiotic resistance in bacteria, particularly Staphylococcus epidermidis, poses a significant threat to public health.
• Understanding the mechanisms of glycopeptide resistance in S. epidermidis is essential for developing effective treatment strategies.

Purpose of the Study:

• To investigate the nature and mechanism of low-level glycopeptide resistance in clinical isolates of Staphylococcus epidermidis.
• To determine if resistance is constitutive or inducible and assess its stability.
• To explore the role of antibiotic binding and sequestration in glycopeptide resistance.

Main Methods:

• Phenotypic characterization of resistance through serial passage in the presence and absence of antibiotics.
• Assessment of antibiotic activity abolition upon exposure to sub-inhibitory concentrations.
• Evaluation of antibiotic-binding activity in resistant and susceptible strains.

Main Results:

• Constitutive, stable low-level glycopeptide resistance was observed in three clinical S. epidermidis isolates.
• Passage in antibiotics did not increase resistance; resistance was not lost in antibiotic-free media.
• Resistant strains showed significantly increased antibiotic sequestration, particularly in stationary phase, with teicoplanin bound more avidly than vancomycin.

Conclusions:

• Glycopeptide resistance in S. epidermidis appears to involve enhanced antibiotic binding/sequestration, potentially at non-target sites.
• The observed resistance is stable and not inducible, suggesting a pre-existing mechanism.
• Teicoplanin is sequestered more effectively than vancomycin by resistant S. epidermidis strains.