Are all community methicillin-resistant Staphylococcus aureus related? A comparison of their mec regions

To compare the relationship of community-acquired, methicillin-resistant Staphylococcus aureus (CMRSA) from five Australian States and New Zealand.

Contour-clamped homogeneous electric field (CHEF) electrophoresis and analysis of the mec complex and ccr gene complex by PCR were used to compare 22 CMRSA isolates from Western Australia (WA), South Australia (SA), Victoria (VIC), New South Wales (NSW) and New Zealand (NZ) and three hospital-acquired epidemic MRSA (EMRSA).

Sixteen community isolates were found to carry Class B mec complex and Type 2 ccr gene complex. Two WA isolates carried the Class B1 mec complex and three VIC and one SA isolate carried a previously unreported mec complex, which has been labelled E. The ccr gene type of the Class B1 and Class E isolates could not be determined. These isolates may carry previously unreported ccr gene complexes. The relatedness of the CHEF patterns of the CMRSA was dependent on their geographical origin. A similar CHEF pattern was found in some WA MRSA, VIC and SA isolates. NSW and NZ CMRSA had the same CHEF patterns and were similar to three VIC isolates and EMRSA-16. Two SA CMRSA isolates had CHEF patterns similar to the English EMRSA-15 strain. A multiply resistant, nosocomial EMRSA from Australia had a class A mec complex, and a CHEF pattern, which was unrelated to any of the CMRSA.

Most of the CMRSA isolated from five Australian states and New Zealand had unrelated CHEF patterns. However, the majority of them carried the Type IV SCCmec cassette (Class B mec and Type 2 ccr gene complexes), which indicates that they may have acquired their mec complex from the same source or that they have evolved from the same progenitor. Some of the CMRSA had a previously undescribed SCCmec cassette.