Novel Rearrangements in the Staphylococcal Cassette Chromosome Mec Type V Elements of Indian ST772 and ST672 Methicillin Resistant Staphylococcus aureus Strains

Abstract

Staphylococcus aureus is a commensal gram positive bacteria which causes severe and non severe infections in humans and livestock. In India, ST772 is a dominant and ST672 is an emerging clone of Staphylococcus aureus. Both cause serious human diseases, and carry type V SCC mec elements. The objective of this study was to characterize SCC mec type V elements of ST772 and ST672 because the usual PCR methods did not amplify all primers specific to the type. Whole genome sequencing analysis of seven ST772 and one ST672 S. aureus isolates revealed that the SCC mec elements of six of the ST772 isolates were the smallest of the extant type V elements and in addition have several other novel features. Only one ST772 isolate and the ST672 isolate carried bigger SCC mec cassettes which were composites carrying multiple ccrC genes. These cassettes had some similarities to type V SCC mec element from M013 isolate (ST59) from Taiwan in certain aspects. SCC mec elements of all Indian isolates had an inversion of the mec complex, similar to the bovine SCC mec type X. This study reveals that six out of seven ST772 S. aureus isolates have a novel type V (5C2) SCC mec element while one each of ST772 and ST672 isolates have a composite SCC mec type V element (5C2&5) formed by the integration of type V SCC mec into a MSSA carrying a SCC element, in addition to the mec gene complex inversions and extensive recombinations.