Typing results of Methicillin-resistant Staphylococcus aureus (MRSA) resulting from the SafeGuard workpackage 2.3 "MRSA vet-net"

Among animals high MRSA colonization rates have been documented especially in livestock (swine, poultry, cattle), which can be the source of zoonotic transmissions. Within work package 2.3 (WP 2.3) of SafeGuard, the partners perform multiple investigations into the occurrence of MRSA among (livestock) animals. The molecular typing of MRSA isolates found in these studies is a central aim of this work package. Since 2009, all MRSA isolated in longitudinal studies and prevalence investigations within the framework of WP 2.3 have been characterized using sequence-based typing of the S. aureus protein A (spa) gene. Spa types were clustered into spa clonal complexes (spa-CC) by the Based Upon Repeat Pattern (BURP) algorithm of the Ridom StaphType software. Results of spa typing were compared to multilocus-sequence typing (MLST) results available on the central spa-server and in recent publications. In total, 2147 MRSA isolates were spa-typed. Among these strains, 83 samples were from humans, 1800 from pigs or pig holdings, 257 from chickens or chicken abattoirs and 7 from other animals (cats, dogs, guinea pigs, cattle and sheep). Overall, 95% of all MRSA isolates were characterized by spa-CC011 (t011, t034, t108, t1184, t1197, t1250, t1255, t1451, t1606, t2330, t2346, t2576, t3423, t4652, t571, t588, t6247, t6320, t7621), indicative for the clonal lineage CC398 as determined by MLST. Ten isolates were associated with spa- CC002/2164 indicative for MLST CC5. Four isolates were found to belong to spa- CC1236/3992 described to represent MLST CC97. Ten spa types (n=61 isolates) indicative for multiple MLST CCs were not clustered with other types (t003, t015, t020, t127, t1430, t151, t1535, t5838, t7496, t899). Six spa types were excluded from BURP analysis due to the spa repeat length (t1344, t1456, t2383, t2510, t3041, t991). MRSA of the CC398 lineage were predominant among the isolates characterized in WP2.3. However, rare MRSA spa types were determined.