Methicillin-Resistant Blood Isolates Harboring a Novel Pseudo-staphylococcal Cassette Chromosome Element.

The aim of this work was to assess a novel pseudo-staphylococcal cassette chromosome (ΨSCC) element in methicillin-resistant (MRSA) blood isolates. Community-associated MRSA E16SA093 and healthcare-associated MRSA F17SA003 isolates were recovered from the blood specimens of patients with bacteremia in 2016 and in 2017, respectively. Antimicrobial susceptibility was determined the disk diffusion method, and SCC typing was conducted by multiplex polymerase chain reaction. Whole genome sequencing was carried out by single molecule real-time long-read sequencing. Both isolates belonged to sequence type 72 and -type I, and they were negative for Panton-Valentine leukocidin and toxic shock syndrome toxin. The -types of E16SA093 and F17SA003 were t324 and t2460, respectively. They had a SCC IV-like element devoid of the cassette chromosome recombinase () gene complex, designated as ΨSCC . The element was manufactured from SCC type IV and the deletion of the gene complex and a 7.0- and 31.9-kb portion of each chromosome. The deficiency of the gene complex in the SCC unit is likely resulting in mobility loss, which would be an adaptive evolutionary mechanism. The dissemination of this clone should be monitored closely.