Multiple Staphylococcal Cassette Chromosomes and Allelic Variants of Cassette Chromosome Recombinases in Staphylococcus aureus and Coagulase-Negative Staphylococci from Norway

Abstract

We investigated the nature of the staphylococcal cassette chromosome mec (SCC mec ) elements and cognate insertion sites in a collection of 42 clinical staphylococcal isolates of various species from Norway. The ccr and mec genes and the attachment sites ( attL / attR ) were identified by PCR, Southern blot hybridization, and DNA sequencing. We found 10 possibly new SCC mec types and one previously unreported variant of SCC mec type III ( mec complex A, ccrAB3 , and ccrC7 ) in Staphylococcus epidermidis, Staphylococcus haemolyticus , and Staphylococcus hominis . Eleven of 42 strains contained multiple copies of ccr , suggesting the presence of mosaic structures composed of multiple SCC elements. S. haemolyticus contained ccrAB2 genes identical to those in S. aureus SCC mec type IV but lacked IS 1272 and mec regulators. Two new allelic ccr variants, ccrC6 and ccrC7 , were identified. Also, the presumed functional version of ccrB1 was found in a mecA -positive S. hominis strain and in mecA -negative S. epidermidis and S. hominis strains. Only minor differences in direct repeats in the left and right boundaries ( attR / attL ) were observed, while there was more variation in the inverted repeats. Coagulase-negative staphylococci (CoNS) contained several representatives of different ccr complexes and thus seemed to harbor multiple or composite new types of SCC mec . The enormous diversity observed in the SCC mec elements implies a large SCC mec reservoir in CoNS.