Clinical Scorecard: Identification of ST3390: A New Apigmented MRSA Variant from the CC5 Lineage
At a Glance
Category
Detail
Condition
Methicillin-resistant Staphylococcus aureus (MRSA) infections, including bloodstream infections and sepsis
Key Mechanisms
Emergence of a novel CC5 MRSA sequence type ST3390 characterized by unique hybrid SCCmec elements, lack of staphyloxanthin pigment due to a conserved deletion in CrtN, and high cytotoxicity towards human neutrophils
Target Population
Patients infected with hospital-associated MRSA strains, particularly those in Tampa, Florida where ST3390 has been identified
Care Setting
Hospital and clinical microbiology laboratories; infectious disease and critical care settings managing MRSA infections
Key Highlights
ST3390 is a rare and novel CC5 MRSA lineage with only 65 recorded global infections, 36 from Tampa.
ST3390 strains lack the staphyloxanthin pigment due to a conserved 6 amino acid in-frame deletion in the CrtN biosynthesis protein.
TPA-ST3390 strains exhibit high cytotoxicity to human neutrophils and virulence in murine sepsis models, indicating hypervirulent properties.
Guideline-Based Recommendations
Diagnosis
Use whole genome sequencing and multi-locus sequence typing (MLST) to identify MRSA lineages including ST3390.
Employ spa-typing and SCCmec characterization to differentiate MRSA strains and detect unique hybrid SCCmec elements.
Management
Recognize the multidrug resistance profile of CC5 MRSA strains conferred by large SCCmec elements (I, II, III) when selecting antibiotic therapy.
Consider the potential hypervirulence of ST3390 strains in clinical management and infection control measures.
Monitoring & Follow-up
Surveillance of MRSA lineages in hospital settings to detect emerging variants like ST3390.
Monitor patient outcomes and infection severity associated with ST3390 to inform treatment protocols.
Risks
ST3390 strains possess hybrid SCCmec elements conferring resistance to multiple antibiotic classes.
Loss of staphyloxanthin pigment may alter bacterial survival but ST3390 remains highly virulent and cytotoxic.
Horizontal gene transfer between HA-MRSA and CA-MRSA lineages may increase virulence and resistance.
Patient & Prescribing Data
Hospitalized patients infected with CC5 MRSA strains, including the ST3390 variant
ST3390 strains carry large SCCmec elements conferring multidrug resistance; antibiotic selection should consider resistance profiles and potential hypervirulence.
Clinical Best Practices
Implement molecular typing (MLST, spa-typing, SCCmec analysis) for accurate MRSA strain identification.
Maintain rigorous infection control to limit spread of hypervirulent and multidrug-resistant MRSA variants like ST3390.
Use phenotypic assays such as neutrophil-killing and blood viability tests to assess virulence potential of clinical isolates.
Consider genomic surveillance to monitor clonal expansion and diversification of MRSA lineages in patient populations.
by Emily A Felton, Mary-Elizabeth Jobson, Nathanial J Torres, Rachel M Washburn, Ariana M Virgillio, Joshua Alvior, Eleonora Cella, Amorce Lima, Deanna Becker, Suzane Silbert, Taj Azarian, Kami Kim, Lindsey N Shaw
