A mecC allotype, mecC3, in the CoNS Staphylococcus caeli, encoded within a variant SCCmecC

Background: Methicillin resistance in staphylococci is conferred by an alternative PBP (PBP2a/2') with low affinity for most β-lactam antibiotics. PBP2a is encoded by mecA, which is carried on a mobile genetic element known as SCCmec. A variant of mecA, mecC, was described in 2011 and has been found in Staphylococcus aureus from humans and a wide range of animal species as well as a small number of other staphylococcal species from animals.

Objectives: We characterized a novel mecC allotype, mecC3, encoded by an environmental isolate of Staphylococcus caeli cultured from air sampling of a commercial rabbit holding.

Methods: The S. caeli isolate 82BT was collected in Italy in 2013 and genome sequenced using MiSeq technology. This allowed the assembly and comparative genomic study of the novel SCCmec region encoding mecC3.

Results: The study isolate encodes a novel mecA allotype, mecC3, with 92% nucleotide identity to mecC. mecC3 is encoded within a novel SCCmec element distinct from those previously associated with mecC, including a ccrAB pairing (ccrA5B3) not previously linked to mecC.

Conclusions: This is the first description of the novel mecC allotype mecC3, the first isolation of a mecC-positive Staphylococcus in Italy and the first report of mecC in S. caeli. Furthermore, the SCCmec element described here is highly dissimilar to the archetypal SCCmec XI encoding mecC in S. aureus and to elements encoding mecC in other staphylococci. Our report highlights the diversity of mecC allotypes and the diverse staphylococcal species, ecological settings and genomic context in which mecC may be found.