Teicoplanin-Resistant Coagulase-Negative Staphylococci: Do the Current Susceptibility Testing Methods Reliably Detect...

Area of Science:

• Medical Microbiology
• Infectious Diseases
• Antimicrobial Resistance

Background:

• Coagulase-negative staphylococci (CoNS) are emerging pathogens, leading to increased antibiotic susceptibility testing (AST).
• Detection of teicoplanin resistance in CoNS is rising, but data are limited and inconclusive.
• Standardized methods for accurate teicoplanin resistance detection in CoNS are lacking.

Purpose of the Study:

• To compare the performance of various AST methods for detecting teicoplanin resistance in CoNS.
• To evaluate the robustness of different AST techniques and identify potential diagnostic algorithms.
• To highlight the challenges and inconsistencies in current teicoplanin resistance testing for CoNS.

Main Methods:

• 162 consecutive CoNS strains initially identified as teicoplanin-resistant by Vitek-2 were tested.
• Methods included standard and high inoculum broth microdilution (sBMD; hBMD), agar dilution (AD) at 24h and 48h, standard and macrogradient diffusion strips (sGDT, MET), screening agar, and disc diffusion.
• sBMD served as the reference method for comparison.

Main Results:

• Significant discrepancies were observed among AST methods, with sBMD identifying the fewest resistant strains.
• Vitek-2 testing reported the highest number of resistant strains, but only 2 were confirmed by other methods.
• sGDT and disc diffusion showed good agreement with sBMD, while AD-24h, hBMD, and AD-48h showed varying rates of false resistance.

Conclusions:

• Current AST methods for teicoplanin resistance in CoNS produce inconsistent and inconclusive results.
• Teicoplanin susceptibility testing is highly sensitive to technical factors, complicating diagnostic algorithm development.
• Further research is needed to clarify clinical teicoplanin efficacy in relation to susceptibility testing outcomes.