Detection of vancomycin resistant Staphylococcus aureus: a comparative study of three different phenotypic screening...

Area of Science:

• Microbiology
• Clinical Diagnostics
• Antimicrobial Resistance

Background:

• Vancomycin is a critical antibiotic for treating Staphylococcus aureus infections.
• Emergence of vancomycin resistance in S. aureus (VRSA) and intermediate susceptibility (VISA) poses a significant public health threat.
• Accurate and rapid screening methods are essential for timely clinical management.

Purpose of the Study:

• To compare the efficacy of three screening methodologies for detecting vancomycin-reduced susceptibility in Staphylococcus aureus.
• To identify the most reliable method for routine diagnostic laboratories.

Main Methods:

• Screening of 160 Staphylococcus aureus clinical isolates and ATCC strains using Hiramatshu, MHA, and CDC methods.
• Determination of Minimum Inhibitory Concentration (MIC) for all isolates using NCCLS methodology.
• Comparative analysis of screening results against established MIC-based classifications.

Main Results:

• All 160 isolates were classified as vancomycin-susceptible by NCCLS criteria (MIC ≤ 4 μg/mL).
• The Hiramatshu method identified 23 positive strains, and MHA identified 2 strains with reduced susceptibility.
• The CDC method accurately identified no vancomycin-intermediate S. aureus (VISA) or vancomycin-resistant S. aureus (VRSA) strains relative to their MICs.

Conclusions:

• The CDC screening method is the most appropriate and reliable for detecting VISA and VRSA in diagnostic laboratories.
• Standard screening methods may yield false positives for vancomycin susceptibility.
• Continued surveillance and validation of screening tools are crucial for combating antimicrobial resistance.