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Updated: Mar 2, 2026
Multiplex PCR Assay for Typing of Staphylococcal Cassette Chromosome Mec Types I to V in Methicillin-resistant Staphylococcus aureus
Published on: September 5, 2013
Identification of a distinctive phenotype for endocarditis-associated clonal complex 22 MRSA isolates with reduced
Helene Marbach1, Eve Boakes1, Steven Lynham2
1Centre for Clinical Infection and Diagnostics Research (CIDR), Department of Infectious Diseases, King's College London & Guy's and St. Thomas' NHS Foundation Trust, London, UK.
Purpose:
We previously identified an association between CC22 meticillin-resistant Staphylococcus aureus (MRSA) bloodstream infection isolates with an elevated vancomycin MIC (V-MIC) in the susceptible range (1.5-2 mg l-1) and endocarditis. This study explores whether these isolates have a specific phenotype consistent with the clinical findings.
Methodology:
CC22 and CC30 MRSA isolates with high (1.5-2 mg l-1) and low (≤0.5 mg l-1) V-MICs were tested for fibrinogen and fibronectin binding, virulence in a Galleria mellonella caterpillar model, phenol soluble modulin production and accessory gene regulator (agr) expression.
Results:
CC22 high V-MIC, but not CC30 high V-MIC isolates, showed sustained fibrinogen binding through a stationary growth phase and increased PSM production, specifically PSMα1, compared with respective low V-MIC isolates. Expression was lower in both CC22 and CC30 high V-MIC isolates compared with respective low V-MIC isolates, although there was no associated reduction in virulence in the caterpillar model.
Conclusions:
The identification of a distinct phenotype for CC22 high V-MIC isolates supports the hypothesis that bacterial factors contribute to the mechanism underlying their association with endocarditis. Further study of these isolates could shed light on the molecular mechanism of endocarditis in humans.
