SaLTy: a novel Staphylococcus aureus Lineage Typer

Area of Science:

• Microbiology
• Genomics
• Epidemiology

Background:

• Staphylococcus aureus is a common human colonizer with significant pathogenic potential, causing fatal infections.
• Existing molecular typing methods do not fully leverage S. aureus whole genome sequences for population structure analysis.
• Accurate sub-grouping of S. aureus is crucial for understanding infection potential and epidemiological trends.

Purpose of the Study:

• To develop a novel, genome-based typing method for Staphylococcus aureus that defines phylogenetic lineages.
• To create a rapid and accurate tool for classifying S. aureus isolates based on population structure.
• To utilize this new typing system for epidemiological surveillance, including tracking methicillin-resistant S. aureus (MRSA).

Main Methods:

• Development of Staphylococcus aureus Lineage Typing (SaLTy) based on alleles of three core genes.
• Validation of SaLTy on 5000 S. aureus genomes, achieving 99.12% accuracy.
• Comparison of SaLTy lineages with existing Clonal Complexes (CCs) from BIGSdb.
• Application of SaLTy for characterizing the carriage and evolution of Staphylococcal chromosomal cassette mec (SCCmec) in MRSA.

Main Results:

• SaLTy successfully divides S. aureus into 61 distinct, phylogenetically congruent lineages.
• The method demonstrates high accuracy (99.12%) in assigning isolates to their correct lineage.
• SaLTy lineages provide a more congruent representation of phylogenetic structure than traditional CCs.
• Analysis of SCCmec carriage across SaLTy lineages revealed variations and temporal dynamics, improving MRSA epidemiology insights.

Conclusions:

• SaLTy is a simple, highly accurate, and rapid method for typing S. aureus based on its fundamental phylogenetic structure.
• The tool effectively analyzes large-scale genome data, aiding in the characterization of S. aureus populations.
• SaLTy enhances the surveillance of S. aureus sub-groups, particularly MRSA, contributing to public health efforts.