Pilot study on nasal microbiota dynamics and MRSA carriage of a pig cohort housed on straw bedding.

Methicillin-resistant Staphylococcus aureus (MRSA) can be transmitted between pigs and humans on farms. Hence, the reduction of MRSA carriage in pigs could decrease the risk of zoonotic transmission. Recently, straw bedding has been found to significantly reduce MRSA carriage in pigs. The mechanisms behind this effect remain unclear but changes in the nasal microbiome may play a role. In this exploratory study, the nasal microbiota of pigs kept on straw was examined using V1/V2 16S rRNA gene sequencing. Nasal swabs were collected from 13 pigs at six different time points during the course of a full fattening cycle resulting in 74 porcine samples. In addition, straw samples were collected at each time point. Eleven out of 13 pigs were MRSA positive at housing-in. We found a strong temporal pattern in the microbial communities. Both microbial diversity and abundance of Staphylococcus species peaked in week 5 after introduction to the straw stable decreased in week 10, when all pigs turned MRSA-negative, and increased again toward the end of the fattening period. These findings show that the introduction of pigs into a new environment has a huge impact on their nasal microbiota, which might lead to unfavorable conditions for MRSA. Moreover, other Staphylococcus species may play a role in eliminating MRSA carriage. We designed a follow-up study including two different husbandry systems to further assess these effects.