Objective
To evaluate BD GeneOhm™ MRSA on a diverse collection of predominantly community-onset MRSA strains.

Methods
353 MRSA strains representing 103 spa-types and the SCCmec-types I to V plus non-typeables were tested by BD GeneOhm™ MRSA in 2006. 49 MSSA isolates (22 spa-types) were included as negative controls. In 2008 a new investigational BD GeneOhm MRSA assay (BD GeneOhm MRSA 2, BD) was used to test 156 of the 353 MRSA isolates (79 spa-types) including all BD GeneOhm™ MRSA false negative isolates and 27 of the 49 MSSA isolates (21 spa-types).

Results
Initially BD GeneOhm™ MRSA failed to detect 57 MRSA strains (16 %, 21 spa-types) of which 84 % harboured SCCmec IVa. After a new DNA purification BD GeneOhm™ MRSA identified 13 of these strains reducing the number of BD GeneOhm™ MRSA negative strains to 44. Three MSSA strains were identified as MRSA. t024-ST8-IVa accounted for 33 % of isolates in Copenhagen in 2006 but only 13 % were identified by BD GeneOhm™ MRSA in the final rounds of thermocycling. BD GeneOhm MRSA 2 assay detected all but two of the BD GeneOhm™ MRSA false negative strains (t688-IVa and t690-V).

Conclusion
BD GeneOhm™ MRSA did not perform well on this collection. Combining BD GeneOhm™ MRSA with BD GeneOhm MRSA 2 greatly improved the test leaving only two isolates false negative. BD GeneOhm™ MRSA can only be used in Copenhagen if combined with BD GeneOhm MRSA 2. Furthermore, due to the constant evolution of SCCmec cassettes we recommend a continuous global surveillance to update the test when necessary.