Accessory Gene Regulator Polymorphism and Vancomycin Minimum Inhibitory Concentration in Methicillin-Resistant...

Area of Science:

• Medical Microbiology
• Infectious Diseases
• Antimicrobial Resistance

Background:

• Methicillin-resistant Staphylococcus aureus (MRSA) bacteremia with vancomycin MIC of 2 µg/mL is associated with high therapeutic failure rates.
• Accessory gene regulator (agr) polymorphism influences vancomycin treatment outcomes.
• Investigating the link between agr polymorphism and vancomycin MICs in MRSA is crucial.

Purpose of the Study:

• To determine the association between accessory gene regulator (agr) polymorphism and vancomycin minimum inhibitory concentrations (MICs) in MRSA isolates.
• To analyze the distribution of agr groups in MRSA isolates with varying vancomycin MICs.
• To identify potential correlations between specific agr groups and reduced vancomycin susceptibility.

Main Methods:

• Agr group-specific PCR was performed on 118 MRSA bloodstream isolates.
• Vancomycin susceptibility testing, including E-test GRD for hVISA detection, was conducted.
• Isolates were categorized by agr group (I, II, III, or unclassified) and vancomycin MIC (0.5, 1, or 2 µg/mL).

Main Results:

• Agr group II was more prevalent in MRSA isolates with a vancomycin MIC of 2 µg/mL (32.6%) compared to non-group II isolates (16%).
• Out of 26 isolates with vancomycin MIC of 2 µg/mL, 9 belonged to agr group I, 14 to agr group II, and 2 to agr group III.
• Three of the four hVISA isolates identified belonged to agr group II.

Conclusions:

• MRSA isolates exhibiting a vancomycin MIC of 2 µg/mL were more frequently observed in agr group II.
• This finding suggests a potential role for agr group II in reduced vancomycin susceptibility in MRSA.
• Further research is warranted to elucidate the mechanisms underlying this association.