Comparative Genomic Analysis of Staphylococcal Cassette Chromosome mec Type V Staphylococcus aureus Strains and Estimation of the Emergence of SCC mec V Clinical Isolates in Korea.

Background: Staphylococcal cassette chromosome mec type V (SCC mec V) methicillin-resistant Staphylococcus aureus (MRSA) has been recovered from patients and livestock. Using comparative genomic analyses, we evaluated the phylogenetic emergence of SCC mec V after transmission from overseas donor strains to Korean recipient strains.
Methods: Sixty-three complete MRSA SCC mec V genomes (including six Korean clinical isolates) were used to construct a phylogenetic tree. Single-nucleotide polymorphisms were identified using Snippy, and a maximum-likelihood-based phylogenetic tree was constructed using RAxML. The possible emergence of the most common ancestor was estimated using BactDating. To estimate mecA horizontal gene transfer (HGT) events, Ranger-dtl was applied to 818 SCC mec V strains using publicly available whole-genome data.
Results: The phylogenetic tree showed five major clades. German strains formed a major clade; their possible origin was traced to the 1980s. The emergence of Korean SCC mec V clinical isolates was traced to 2000-2010. mecA HGT events in Staphylococcus spp. were identified in seven strains. P7 (Hong Kong outbreak strain) served as the donor strain for two Korean sequence type (ST) 59 strains, whereas the other five recipient strains emerged from different SCC mec V donors.
Conclusions: Most Korean SCC mec V strains may have emerged during 2000-2010. A unique MRSA SCC mec V strain, ST72 (a Korean common type of community-associated MRSA), was also identified. The genomic dynamics of this clone with a zoonotic background should be monitored to accurately understand MRSA evolution.