Abstract
In the early 2000s, a particular MRSA clonal complex (CC398) was found mainly in pigs and pig farmers in Europe. Since then, CC398 has been detected among a wide variety of animal species worldwide. We investigated the population structure of CC398 through mutation discovery at 97 genetic housekeeping loci, which are distributed along the CC398 chromosome within 195 CC398 isolates, collected from various countries and host species, including humans. Most of the isolates in this collection were received from collaborating microbiologists, who had preserved them over years. We discovered 96 bi-allelic polymorphisms, and phylogenetic analyses revealed that an epidemic sub-clone within CC398 (dubbed ‘clade (C)’) has spread within and between equine hospitals, where it causes nosocomial infections in horses and colonises the personnel. While clade (C) was strongly associated with S. aureus from horses in veterinary-care settings (p = 2×10−7), it remained extremely rare among S. aureus isolates from human infections.
Highlights
Staphylococcus aureus is a frequent nasal coloniser of mammals and birds
CC398 has been the dominant livestock-associated methicillin-resistant S. aureus (MRSA) (LA-MRSA) among pigs in several countries [6,7,8,9,10,11], but CC398 has been found in various other livestock species [12,13,14,15,16,17,18,19,20]
Molecular typing In this study, a convenience sample collection of 195 S. aureus isolates, including MSSA (n = 37) and MRSA (n = 158), was investigated (Table 1)
Summary
Staphylococcus aureus is a frequent nasal coloniser of mammals and birds. In humans, it is a leading cause of a wide range of infections in hospitals and communities. In addition to being a major threat to human health, since the 2000s MRSA is widely disseminated as a coloniser and infectious agent in economically important livestock and companion animals including cows, sheep, goats, poultry, pigs, dogs and horses. The first sporadic reports of MRSA infections in livestock arose during the 1970s and in companion animals (dogs and cats) during the late 1980s and 1990s [2,3,4]. Several studies have reported human cases of methicillin-sensitive CC398 without current contact with livestock [21,26,27]
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