Characterization of a novel, type II staphylococcal cassette chromosome mec element from an endemic oxacillin-resistant Staphylococcus lugdunensis clone in a hospital setting.

Background: Staphylococcus lugdunensis is a significant pathogen that causes community-acquired and nosocomial infections. The high prevalence of oxacillin-resistant S. lugdunensis (ORSL) is of major concern. Resistance to β-lactams is caused by acquisition of the staphylococcal cassette chromosome mec (SCCmec) element. The cassette is highly diverse, both structurally and genetically, among CoNS. Isolates carrying SCCmec II-ST6 are the major persistent clones in hospitals.

Objectives: To investigate the structure and evolutionary origin of a novel type II SCCmec element in an endemic ST6 S. lugdunensis clone.

Methods: The structure of the SCCmec II element carried by ST6 strain CGMH-SL118 was determined by WGS and compared with those reported previously.

Results: A novel 39 kb SCCmec element, SCCmecCGMH-SL118, with a unique mosaic structure comprising 41 ORFs integrated into the 3' end of the rlmH gene, was observed. Some regions of SCCmecCGMH-SL118 were homologous to SCCmec IIa of the prototype MRSA strain N315. The structure of SCCmecCGMH-SL118 was similar to that of SCCmec IIb of the MRSA strain, JCSC3063, mainly lacking the aminoglycoside resistance determinant pUB110 in the J3 region but containing the insertion sequence IS256 in the J2 region. Notably, SCCmecCGMH-SL118 deletions in the J1 region compared with SCCmec types IIa and IIb, and a high homology to SCCmec elements of Staphylococcus aureus JCSC4610 and Staphylococcus haemolyticus strain 621 were found.

Conclusions: The genetic diversity of the type II SCCmec element in ORSL suggests that CoNS is a potential reservoir for interspecies transfer of SCCmec to S. aureus in hospitals.