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Methicillin-susceptible Staphylococcus aureus (MSSA) and methicillin-resistant Staphylococcus aureus (MRSA) are
colonizers of skin and mucosa. Studies about MSSA and MRSA in human patients showed a competition of these
two microorganisms for colonization space in the anterior nares. Moreover, in humans one clone can be found rather
than differing types of MSSA and MRSA. Concerning a potential control strategy, this could also be important for
pigs. Therefore, the aim of this study was to investigate the colonization dynamics of both MSSA and MRSA in pigs
over a longer time period and investigate their clonal diversity.
Materials and Methods
Eighteen pigs were sampled three times every ten weeks with a nasal swab. Additionally, environmental samples
such as swabs of walls, toys, brushes, watering places and troughs were taken. All samples were investigated for
MSSA and MRSA, respectively. Spa-typing was done with up to five MRSA and MSSA isolates, respectively, found
per sample and time point. Of almost 400 MSSA and MRSA isolated, 62 isolates were further investigated by microarray.
We found three pigs to be non-carriers and twelve were colonized with both MRSA and MSSA. In 14 out of 54 samples
taken from all animals over all-time points MSSA were found, only. In comparison, nine samples were exclusively
MRSA-positive. Spa-types of MSSA and MRSA were mostly different with CC398 associated spa-types within
MRSA isolates, whereas CC9 associated spa-types predominate as MSSA in both, pigs and their environment.
Moreover, strains of the same clonal lineage showed a high genetic identity despite their origin.
The results do not support the hypothesis of a competitive colonization of MSSA and MRSA in the anterior nares of
pigs. Rather we found a changing status. Hence, highly identic clones of MSSA and MRSA, respectively, are present
in the anterior nares of pigs and their environment.