# Genomic evolution of ST228 SCCmec-I MRSA 10 years after a major nosocomial outbreak

## TL;DR

This study explores how a hospital-associated MRSA clone evolved genetically over 10 years after a major outbreak, linking its decline to infection control measures and genetic changes.

## Contribution

The study identifies specific genes associated with MRSA epidemicity and highlights the role of genomic evolution in the decline of a major MRSA clone.

## Key findings

- A genome-wide association study identified genes linked to high or low epidemic success in MRSA strains.
- A gene related to fibrinogen binding was found to be the most influential predictor of MRSA epidemicity.
- The decline of the MRSA clone coincided with infection control measures and genetic drift.

## Abstract

In this study, we investigated the genomic changes in a major methicillin-resistant Staphylococcus aureus (MRSA) clone following a significant outbreak at a hospital. Whole-genome sequencing of MRSA isolates was utilized to explore the genomic evolution of post-outbreak MRSA strains. The epidemicity of the clone declined over time, coinciding with the introduction of multimodal infection control measures. A genome-wide association study (GWAS) identified multiple genes significantly associated with either high or low epidemic success, indicating alterations in mobilome, virulence, and defense mechanisms. Random Forest models pinpointed a gene related to fibrinogen binding as the most influential predictor of epidemicity. The decline of the MRSA clone may be attributed to various factors, including the implementation of new infection control measures, single nucleotide polymorphisms accumulation, and the genetic drift of a given clone. This research underscores the complex dynamics of MRSA clones, emphasizing the multifactorial nature of their evolution. The decline in epidemicity seems linked to alterations in the clone’s genetic profile, with a probable shift towards decreased virulence and adaptation to long-term carriage. Understanding the genomic basis for the decline of epidemic clones is crucial to develop effective strategies for their surveillance and management, as well as to gain insights into the evolutionary dynamics of pathogen genomes.