Methicillin-sensitive and Methicillin-resistant Staphylococcus aureus in pigs: (co-) colonization dynamics and clonal diversity

Methicillin-susceptible Staphylococcus (S.) aureus (MSSA) and methicillin-resistant S. aureus (MRSA) are colonizers of skin and mucosa. In humans, MSSA and MRSA compete for colonization space in the anterior nares and one clone can be found rather than differing types of MSSA and MRSA. We investigated the colonization dynamics and clonality of both, MSSA and MRSA in pigs over a longer time period. Eighteen sows were nasally sampled three times every ten weeks. Additionally, environmental samples were taken. Samples were investigated for MSSA and MRSA, respectively. Spa-typing was done with up to five MRSA and MSSA isolates found per sample and time point; selected isolates were further investigated by microarray. 38.9 % of sows were infrequently MSSA/MRSA co-colonized and 16.7 % were permanent carriers of MSSA. The majority of sows showed a changing colonization status. CC398 and CC9 associated spa-types were exclusively found among MRSA and MSSA, respectively. In 44.4 % of sows at least two different types of MSSA were present at the same time and sample. Strains of the same clonal lineage showed a high genetic identity despite their origin. MSSA of different spa-types but 100 % identical microarray profiles were found in sows and their environment. Our results show that pigs may be colonized with MSSA and MRSA at the same time, i.e. that MSSA/MRSA do not exclude each other in the anterior nares of pigs. Highly identic clones are present in sows and their environment, but pigs can be colonized with different clones at the same time.