Clinical Report: Identification and Characterization of ST3390, a Novel Apigmented MRSA Variant

Overview

ST3390 is a newly identified, rare MRSA variant within the CC5 lineage, notable for its lack of staphyloxanthin pigment and high virulence. Predominantly found in Tampa, these strains exhibit unique genomic features including hybrid SCCmec elements and increased cytotoxicity towards human neutrophils.

Background

Methicillin-resistant Staphylococcus aureus (MRSA) remains a significant cause of antibiotic-resistant infections worldwide. The CC5 lineage is a major hospital-associated MRSA group known for multidrug resistance but generally less virulent than community-associated MRSA strains. Recent emergence of hypervirulent CC5 variants has blurred distinctions between hospital- and community-associated infections. Understanding novel variants like ST3390 is critical for tracking MRSA evolution and managing infections.

Data Highlights

Key Findings

• ST3390 is a novel MRSA sequence type within the CC5 lineage, identified primarily in Tampa, Florida.
• All ST3390 strains lack the characteristic staphyloxanthin pigment due to a conserved 6 amino acid deletion in the CrtN biosynthesis protein.
• Genomic analysis reveals unique hybrid SCCmec elements combining features of SCCmecIa, IIa, and VIII, contributing to multidrug resistance.
• TPA-ST3390 strains demonstrate significantly higher cytotoxicity against human neutrophils compared to other CC5 lineages.
• ST3390 strains are virulent in animal models of sepsis, indicating potential for serious invasive infections.
• Phylogenetic and spa-type analyses show diverse spa-types with a unique t010 cluster exclusive to Tampa strains.

Clinical Implications

The emergence of ST3390 highlights the ongoing evolution and diversification of MRSA within hospital and community settings. Its apigmented phenotype may affect detection and immune evasion, while its high virulence and multidrug resistance necessitate vigilant surveillance and tailored antimicrobial strategies. Clinicians should be aware of this variant's potential for severe infections and consider genomic typing in epidemiological investigations.

Conclusion

ST3390 represents a rare but clinically significant MRSA variant within the CC5 lineage, combining unique genomic features with enhanced virulence. This study advances understanding of MRSA clonal expansion and underscores the need for continued monitoring of emerging pathogenic strains.

References

1. Identification of ST3390: A New Apigmented MRSA Variant from the CC5 Lineage