Investigating a rare methicillin-resistant strain: first description of genome sequencing and molecular characterization of CC15-MRSA.

PURPOSE

Methicillin resistant CC15 strains (CC15-MRSA) have only been sporadically described in literature. This study was carried out to describe the genetic make-up for this rare MRSA strain.

METHODS

Four CC15-MRSA isolates collected in Riyadh, Saudi Arabia, between 2013 and 2014 were studied. Two isolates were from clinical infection and 2 from retail meat products. Whole genome sequencing was carried out using Illumina HiSeq2500 genome analyzer.

RESULTS

All the CC15-MRSA isolates had the multilocus sequence typing profile ST1535, 13-13-1-1-81-11-13, which is a single locus variant of ST15. Of the 6 contigs related to the SCC element, one comprised a recombinase gene , , and a helicase, another one included , , and 1 had and . The SCC element had 5 transposase genes, namely 3 identical paralogs of tnpIS431 and 2 identical paralogs of tnpIS256. Two identical copies of a tnpIS256-based insertion element flank the gene. Two copies of this insertion element were present with 1 located in the SCC element and another inserted into the gene. A short 3 kb region, which lacks any bacteriophage structural genes and site-specific DNA integrase, was inserted into the gene. The and the 5'-part of the gene are replaced by a copy of the paralogs from giving rise to a new chimeric paralog in .

CONCLUSION

CC15-MRSA shows a novel SCCV/SCC composite element. Its variant of probably facilitated uptake of foreign mobile genetic elements that promoted emergence of CC15-MRSA. Close surveillance is needed to monitor spread and emergence of further CC15 MRSA strains.