Genomic characterization of a paediatric MRSA outbreak by next-generation sequencing

Abstract

Twelve strains of meticillin-resistant Staphylococcus aureus (MRSA) isolated during a suspected outbreak in a paediatric intensive care unit were analysed by whole-genome sequencing (WGS). To define the clonality of MRSA strains to a high discriminative power, and to evaluate the presence of genetic determinants responsible for antibiotic resistance and virulence. Ten out of 12 strains belonged to multi-locus sequence type ST2625, while the other two strains were ST8. Among the ST2625 strains, analysis based on 1126 genes showed that they were clonal, sharing more than 98.3% of allelic identities, and one strain was isolated from a healthcare worker. All ST2625 strains were characterized by the SCC-Mec cassette IVa, and resistoma analysis indicated correspondence between phenotypic and genotypic characteristics. The study of 63 genes associated with virulence was correlated with the pattern of clonality shown. This analysis confirmed the occurrence of an outbreak. As such, standard infection control measures were strictly enforced, and this led to prompt termination of the outbreak.