AbstractsBiology & Animal Science

Staphylococcus aureus is a common colonizer of the skin and mucous of humans and other mammals while dogs are the major host for Staphylococcus pseudintermedius. The epidemiology and ecology of these bacterial species in animals has gained interest in the last years, not only for their importance in veterinary medicine, due to the increment of infectious processes caused by these pathogens (especially by methicillin resistant strains and other antibiotics of interest), but for its increasingly evidenced zoonotic potential. Since 2005, we are facing the spread of livetock-associated methicillin-resistant S. aureus (LA-MRSA) ST398, especially as colonizer of pigs, and the emergence of multidrug resistant methicillin resistant S. pseudintermedius strains (MRSP) in dogs. On the other hand, methicillin-susceptible strains (MSSA and MSSP) play an essential role in the evolution of different genetic lineages. In the first chapter of this thesis, the nasal presence and characterization of S. aureus and S. pseudintermedius strains of dogs, cats and their owners from 43 households were investigated. A total of 42% of owners and 12% of pets were S. aureus carriers. The corresponding rates for S. pseudintermedius were 22.7 and 4.5 for dogs and humans, respectively. Five cases of direct inter-species transmission (same strain on owner and pet) and 5 cases of possible indirect transmission (S. aureus in dogs or S. pseudintermedius in humans) were detected. The carriage dynamics of 7 of these residences along one year was investigated and revealed that dogs are normally transient S. aureus carriers and that dog owners may be persistently colonized by S. pseudintermedius. S. pseudintermedius isolates were more clonally diverse and dynamic in time than S. aureus. Dogs seem to play a relevant role in the staphylococcal species distribution and colonization of in-contact individuals. The detection of several MSSA ST398 from humans with not contact to livestock supports the hypothesis that LAMRSA ST398 may have emerged from humans. In a second chapter, kennel dogs were investigated for the presence and characterization of both bacterial species. High relative MRSP (8%), moderate MSSP (15.3%) and high MSSA (24.5%) nasal carriage rates were revealed. The predominance of multidrug resistant MRSP ST71 among the MRSP lineages detected reflects the success of this clone also in Spain. Distinct phenotypic and genotypic characteristics were revealed among MRSP and MSSP strains. The detection of traditionally human and livestock associated S. aureus suggests the ability of dogs to carry common S. aureus lineages of in-contact environments. MSSA ST398 was the predominant lineage detected, suspecting a more extended host spectrum of this sub-lineage than considered. The comparative analysis of the S. aureus and S. pseudintermedius isolates recovered from household individuals and pound dogs revealed higher levels of antimicrobial resistance and higher virulence gene contend in S. aureus isolates from household individuals. In the third chapter,…