Novel staphylococcal cassette chromosome mec (SCCmec) type XIV (5A) and a truncated SCCmec element in SCC composite islands carrying speG in ST5 MRSA in Japan.

BACKGROUND

Staphylococcal cassette chromosome mec (SCCmec) elements are highly diverse and have been classified into 13 types. The arginine catabolic mobile element (ACME) is an SCC-like element harbouring an arginine deiminase pathway gene cluster (ACME-arc). ACME type I (ACME I), additionally including a spermidine/spermine-N1-acetyltransferase gene (speG), is considered to have contributed to the rapid spread of the most successful MRSA clone, USA300.

OBJECTIVES

To characterize the SCC composite islands (SCC-CIs) in ST5 MRSA positive for both ACME-arc and speG.

METHODS

Three ST5 MRSA strains (SC640, SC792 and SC955) collected in Hokkaido, Japan were subjected to WGS and the SCC-CIs were determined.

RESULTS

The SCC-CIs consisted of four (SC640 and SC792) or three (SC955) SCC/SCC-like elements and commonly harboured both an ACME type II' and an SCC encoding speG. These SCC-CIs appear to mimic ACME I in USA300, in that they are equipped with ACME-arc and speG. The SCC-CIs of SC640 and SC792 contained novel SCCmec/SCCmec-like elements at the 3' end, whereas SC955 contained SCCmec type V. The SCCmec of SC792 carried mec complex A and ccrC1, which was determined to be novel and designated as SCCmec type XIV (5A). SC640 harboured an SCCmec-like element derived from SCCmec type XIV. It lacked most of the downstream region of the mec complex, including the left chromosomal attachment site (SCCmec XIV Δkdp/DR-L), and lost its capability for chromosomal excision, suggesting that the mecA gene is immobilized on the chromosome.

CONCLUSIONS

These findings provide evidence for increasing complexity of SCC-CIs.