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Although the occurrence of methicillin-resistant Staphylococcus aureus (MRSA) is known
in different healthy livestock species, there are only little data on the emission amounts and dispersion distances of these resistant bacteria from farm buildings via the aerial route. Therefore, this study determined the presence and concentration of MRSA in the ambient air and on surrounding ground surfaces of different animal farms in order to give an estimate of the environmental load. Six pig farms were investigated
four times within one year and five turkey as well as two broiler farms were analyzed
four and three times, respectively within one fattening period. Different samples were
collected inside (samples of animals and their direct surrounding including air) and outside (air, ground surfaces). All samples were analyzed for the presence of MRSA. Selected isolates were spa typed and grouped as Livestock associated (LA)-MRSA according to their association to the clonal complex (CC)398.
MRSA was found regularly on ground surfaces downwind of the pig (73% of 67 samples) and
poultry barns (44.4% of 81 samples), up to the planned investigated distance of 500 m. MRSA
was detected in exhaust air samples from three pig farms and two turkey farms, however,
with very low concentrations between 7 and 93 cfu/m3. Inside the barn MRSA occurred
in samples of animals in high prevalences but also in barn air with higher concentrations than outside as well as regularly in dust and in some fecal samples. Isolates originating from inside and outside the farms were of the same spa types. The relevance of the emission of MRSA from livestock holdings to the environment has to be discussed critically. Neighbouring residents, livestock and wild animals might be exposed and even contaminated via the air and also via contaminated ground surfaces.
However, MRSA concentration in the exhaust air was relatively low. This makes a direct
airborne colonization of animals and people housed or living in close vicinity of livestock
farms rather unlikely. The role of deposited MRSA and thus a potential contamination of
crops used for food and feed are not yet well understood. This needs to be studied in more
detail, in particular in respect to the survival times of deposited MRSA. We conclude that
there seems to be no acute health risk for neighbouring farms or residents due to MRSA emissions from animal husbandries. However, further studies need to verify this presumption.