Carriage frequency, diversity and methicillin resistance of Staphylococcus aureus in Danish small ruminants

The ecology of Staphylococcus aureus in animals has recently gained attention by the research community due to the emergence of livestock-associated methicillin-resistant strains (MRSA). We investigated carriage frequency and clonal diversity of S. aureus in 179 sheep and 17 goats in Denmark using spa typing and MLST. S. aureus was detected in 74 sheep (41%) and 11 goats (64%). The isolates belonged to 26 spa types (including six novel spa types) and 12 STs (including three novel STs). The most common lineage was ST133, which was found in 65% sheep and 55% goats. MRSA was found in three animals and two of them harboured mecC and corresponded to the same lineage (ST130, t843) previously reported in mecC-associated human MRSA infections in Denmark. The remaining MRSA isolate belonged to ST398 but its recovery in sheep could be a consequence of cross contamination due to contact with pigs. This study provides novel data about the occurrence of S. aureus in small ruminants, revealing high carriage frequency and diversity in these animals. The finding of mecC in ovine ST130 isolates suggests that sheep may be a reservoir of this new emerging MRSA clone of suspected animal origin. Inclusion of sheep in national MRSA surveillance programmes in animals is advisable in view of this finding.