Community-acquired methicillin-resistant from ST1 lineage harboring a new SCC IV subtype (SCC IVm) containing the gene.

A pivotal event in the evolutionary path of methicillin-resistant (MRSA) is the acquisition of the staphylococcal cassette chromosome (SCC) element carrying the gene, the determinant of methicillin resistance. Community-acquired (CA) MRSA is commonly associated with skin/soft tissue infections, and doxycycline is one of the drug choices for this purpose. Doxycycline resistance is associated with the acquisition of the gene carried by the plasmid pT181, which may also be integrated into SCC III and V. The aim of this study was to describe a novel SCC IV subtype (IVm) carrying and reveal the genetic context of this element. The SCC sequence was obtained by whole-genome sequencing of the MRSA strain 2288 (ST1 CA-MRSA) and genomic analysis performed using different bioinformatics tools. A copy of pT181 was found to be integrated in the new SCC IVm of the strain 2288. The SCC IVm has high nucleotide identity (99%) with SCC IVa of the strain MW2, except for the J3 region, where the pT181 - carrying gene - is inserted. Inverted repeats (IRs) flanking pT181 were found in this region, suggesting the occurrence of recombination events. The strain 2288 ( type t125) shares most of the virulence attributes with MW2 ( type t128), which is recognized in the past as a cause of severe infections in children in USA. The pattern of branching in the phylogenetic tree depicts a recent common ancestor shared by the 2228 strain and other MRSA from USA, including ERS410852, TCH70, CIG1835, CO-41, MW2, and USA400-0051, but none of them carried pT181. This study also showed that the carried by SCC IVm is functional, determining resistance to doxycycline and tetracycline. The potential dissemination of the and genes in the same genetic event by the acquisition of this new SCC subtype is of concern for community infections.