Molecular epidemiology of PFGE non-typeable meticillin-resistant Staphylococcus aureus in the Netherlands

Abstract number: P1407

Huijsdens X.W., Bosch T., Haenen A., van Santen-Verheuvel M.G., Spalburg E., Heck M.E.O.C., Pluister G.N., van Luit M., Tiemersma E.W., de Neeling A.J.

Objectives: Recently, pigs were identified as a possible new reservoir for community-acquired meticillin-resistant Staphylococcus aureus (CA-MRSA). These pig-related MRSA strains can easily be identified by pulsed-field gel electrophoresis (PFGE). In PFGE, no banding pattern is obtained, due to methylation of the SmaI site, and was from then on referred to as non-typeable (NT)-MRSA. From 2003 to 2007 the number of NT-MRSA was increasing rapidly and pig-to-human transmission had occurred.

The present study gives an overview of the NT-MRSA in the Netherlands in 2007, the characteristics of the NT-MRSA and the clonal structure of these strains. The data will show the importance of this relatively new CA-MRSA strain.

Methods: In the Netherlands, the National Institute of Public Health and the Environment (RIVM) serves as the national reference centre for surveillance of MRSA. All first MRSA isolates, one per patient, are sent to the RIVM for PFGE typing. From this MRSA database all NT-MRSA isolates of 2007 were used for further characterisation.

Molecular typing included staphylococcal protein A (spa) typing, staphylococcal cassette chromosome mec (SCCmec) typing, and multilocus sequence typing (MLST).

Results: Up till November 2007, a total of 535 MRSA isolates were non-typeable by PFGE. Spa typing revealed 24 different spa types. Most of the spa types were closely related, indicating a clonal complex. The two most prevalent spa types were t011 and t108. All NT-MRSA belonged to SCCmec type IV or V and were ST398.

Conclusion: In 2007 approximately 30% of all MRSA isolates were non-typeable. This new CA-MRSA of zoonotic origin appears to spread rapidly, not only in the Netherlands but also in Europe. In the Netherlands MRSA guidelines are changed due to this new strain.