Screening method for detecting staphylococci with reduced susceptibility to teicoplanin

Area of Science:

• Clinical Microbiology
• Infectious Diseases
• Antimicrobial Resistance

Background:

• Increasing incidence of staphylococcal infections with decreased susceptibility to teicoplanin (Minimum Inhibitory Concentration [MIC] >= 8 microg/ml).
• Limitations of standard disk diffusion tests in detecting low-level teicoplanin resistance.
• Challenges in identifying heterogeneous teicoplanin resistance phenotypes.

Purpose of the Study:

• To evaluate a novel agar screening method for detecting staphylococci with decreased susceptibility or heterogeneous resistance to teicoplanin.
• To optimize inoculum density and teicoplanin concentration for an effective agar screening assay.

Main Methods:

• Tested 39 genetically distinct staphylococcal strains (15 resistant, 24 susceptible) on Mueller-Hinton agar.
• Evaluated different inoculum densities (10^5 and 10^6 CFU/ml) and teicoplanin concentrations (6 and 8 microg/ml).
• Selected optimal conditions: 10^6 CFU/spot inoculum and 8 microg/ml teicoplanin concentration.

Main Results:

• The optimized agar screening method successfully detected all strains with teicoplanin MICs >= 8 microg/ml.
• Heteroresistant strains were also accurately identified by the screening method.
• The method demonstrated high efficacy in identifying staphylococci with reduced teicoplanin susceptibility.

Conclusions:

• The developed agar screening method is a reliable tool for detecting staphylococci with decreased susceptibility to teicoplanin.
• This method aids in the early identification of challenging teicoplanin resistance phenotypes.
• Implementation of this screening method can improve patient management for staphylococcal infections.