Epidemiology of multi-drug resistant staphylococci in cats, dogs and people in Switzerland

Background: The human relationship with cats and dogs has been suggested to be of potential concern to public health because of the possible role of pets as reservoir of antibiotic resistant microorganisms. Here I suggest the “One Health” interdisciplinary approach to be helpful towards the understanding of the role of pets in antibiotic resistance spreading, considering also the socio-emotional context of the human-pet relationship.
Methods: I investigated the presence of multi-drug resistant (MDR) staphylococci in cats, dogs and people in the nursing homes and in the community of four Swiss Cantons (Berne, Ticino, Vaud and Zurich). The study received ethical clearance from the responsible Cantonal Ethical Committees and authorization for animal experimentation from the Cantonal and Federal Veterinary Offices. Between March 2008 and December 2009 I collected nasal swabs from 978 people and nasal and ear swabs from 256 dogs and 277 cats and checked them for the presence of staphylococci. Isolated bacteria were identified and their phenotypic antibiotic resistance profile evaluated. Questionnaires on demographic information, health status and human–pet contact were completed by each participant and for each animal investigated.
Results: Rapid and reliable identification of staphylococci by matrix assisted laser desorption ionisation – time of flight mass spectrometry (MALDI-TOF MS) was a pre-requisite to understand the distribution of Staphylococcus spp. in people and pets, also to differentiate among phylogenetically close related species such as S. delphini, S. intermedius, and S. pseudintermedius. The analysis of the staphylococcal population composition of healthy cats and dogs revealed that S. pseudintermedius was present in 27 % (70/256) of healthy dogs and 3 % (8/277) of healthy cats, whereas S. felis was isolated only from cats and represented 31 % of their coagulase-negative staphylococcal isolates. About 17 % (92/533) of pets carried MDR Staphylococcus spp. strains. Previous hospitalisation (stay in a veterinary clinic during at least one night) was identified as a risk factor for the carriage of these strains in nostril and ear of cats and dogs. However, although a relevant proportion of pets and nursing home residents was found to be carrier of MDR staphylococci, the residents had no increased risk of being carriers of these strains when living in homes with pets or having contact with these animals at least once a week. Findings suggested limited strain transmission between pets and humans. I could show strong physical closeness of pets with their owners in households and the high emotional importance of this relationship, but I did not observe any evident impact of pets on carriage of MDR staphylococci in their owners.
At the end of my study I also analysed the clinical implications of methicillin-resistant S. pseudintermedius (MRSP) infections using as an example the isolation of this microorganism from a pyoderma lesion in a dog that underwent various antibiotic treatments before the correct diagnosis was made and an appropriate antibiotic treatment was administered.
Discussion and conclusions: MDR staphylococci were recovered in relevant proportions from healthy pets and people. I could document the potential for exchange of strains due to close physical contact between their hosts. My results, however, indicated negligible rates of MDR staphylococcal transmission between human and pets.
In evaluating the role of pets as reservoir of antibiotic resistant staphylococci, the network of contacts and their physical intensity, together with information on multi-drug resistance carriage in humans and pets should be considered for a correct estimation of the transmission and distribution of antibiotic resistant strains among different hosts.