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Over the last years, more and more infections with methicillin-resistant Staphylococcus aureus (MRSA) have been detected in human and veterinary medicine.
Since 2005, the clonal complex 398 (CC398) is described in livestock and also in humans with exposure to colonized animals.The emergence of this pathogen leads to the question of host adaptation and pathopotency. The evolutionary origin of CC398 in particular is of greater interest. This study deals with the population structure of CC398 by using SNP-analysis.We investigated the population structure of CC398 detecting mutations among 100 housekeeping genes of 112 isolates. This convenience collection included strains from Germany, Belgium, Austria, the United Kingdom, the USA, the Netherlands and Italy. Isolates of humans, pigs, horses, cattle, poultry, dogs, environment, a goat and a cat were chosen.
The dHPLC method was employed and resulting polymorphic PCR products were sequenced subsequently. Data analysis and the construction of a minimum spanning tree were performed by use of Bionumerics 6.0. On the basis of occurring polymorphisms, details about the emergence and geographic spread of MRSA in pigs and other animals and their relationship to MRSA causing infections in humans were displayed. In total, 60 SNPs, representing approximately 1, 5% (41.199bp) of the whole S. aureus-genome, were analysed and 36 haplotypes were differentiated among the 102 strains. The data showed that different haplotypes appeared at different times in various countries. In addition, some isolates clustered according to their geographic origin. Isolates from middle Europe seem to be more diverse. Here, an exclusive host specifity for certain haplotypes was not detected.
A transmission study on two farms was performed in order to get insights into the dynamics of CC398-transmission from human to pigs and vice versa. Transmission of certain haplotypes between pigs and humans seems to be evident according to the resulting data. However, farmers were found to be colonized with different haplotypes during the study period. This study supports that SNP-analysis is a more exact tool for transmission studies than spa-analysis alone. In the future, research on evolutionary processes using sequencing methods of selected genloci or whole genomes will play an important role.