Learn your mec-A-B-C's!

Remember the divergent mecA homologue that we blogged about last year, the one not detected by conventional PCR tests? This livestock-associated strain was described in Lancet and AAC as causing human disease in the UK and Denmark (and now France, and probably elsewhere).

Assuming that bacteria will continue to evolve, and that we will continue to track their spread, new mecA homologues will undoubtedly be discovered. Recognizing this, the IWG-SCC (International Working Group on the Classification of Staphylococcal Cassette Chromosome Elements—a shadowy international cabal obsessed with classifying staphylococcal chromosomal elements) has a short but lucid commentary on how these novel mecA homologues should be reported. As outlined in the table below (from the paper), the guideline suggests using letters and numbers to distinguish new homologues based upon the % nucleotide sequence identity compared with the prototype mecA strain (N315). Using this nomenclature, the strain we previously discussed (LGA251) is now mecC.