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Staphylococcus (S.) aureus colonizes the skin and mucosa of various mammalian hosts, and up to 30% of the human population is permanently colonized. As a zoonotic pathogen, S. aureus plays an important role in both human and veterinary medicine, affecting a broad range of animals. When the general condition of the (animal or human) patient allows the bacteria to cause an infection, the diseases range from superficial to life-threatening. Especially infections with methicillin-resistant S. aureus (MRSA) are a major burden in medicine due to limited treatment options. The increasing detection of MRSA as causative agent of purulent infections in companion animal patients like dogs, cats and horses in the recent past resulted in a discussion about the general relevance and impact of this observation for these animals as well as for Public Health. In consequence, several localized studies investigated and reported MRSA infection frequencies. Further, genotypic characterization of MRSA from companion animal origin indicated the occurrence of genotypes that are also commonly reported in human medicine. The aim of this study was to obtain data on the frequency, geographic origin as well as information on numerous molecular characteristics of S. aureus isolated from infected dogs, cats and horses. Thus, this work provides for the first time both reliable and representative data, obtained by investigation of a large sample size within Germany.
Results achieved by the analysis of 5,229 wound swabs from dogs, cats and horses demonstrated the importance and impact of S. aureus in general, and MRSA in particular, as a cause of wound infections in companion animals in Germany. The detected high MRSArates (62.7% for dogs, 46.4% for cats and 41.3% for horses) within this study are especially worrisome since multi-drug resistance in many of these strains leads to decreased therapeutic options. Genotypic characterization of MRSA, that was performed by use of various typing methods, identified in samples from dogs and cats mainly genetic lineages that are also relevant for infections in humans within Germany (for example clonal complexes CC5 and CC22). These results proof once more the existence of S. aureus belonging to extended host spectrum genotypes (EHSG) with the ability to infect several hosts. For MRSA of equine origin, most of the isolates (87.7%) belonged to CC398, a genetic lineage that can be isolated from livestock, dogs, cats and humans. The emergence of CC398-MRSA as predominant genotype in equine wound infections demonstrates the adaptive capacity of this lineage to other hosts respective niches than livestock and humans, showing an epidemiological change over time of dominating MRSA genotypes in horses.
Further comparative analysis of EHSG-S. aureus originating from companion animals and humans based on various genetic characteristics by use of spa typing, multilocus sequence typing (MLST), pulsed field gel electrophoresis (PFGE) and DNA microarray analysis revealed a lack of host adaptation for both, methicillin-resistant as well as methicillinsusceptible (MSSA) isolates. Thus, MSSA from companion animals have to be considered as EHSG as well. The minor variations of all investigated S. aureus was independent of each respective host origin but rather displayed the natural variation within each investigated lineage.
In conclusion, wound infections caused by S. aureus are a burden in companion animal medicine and the identified high infection rates with MRSA are of special concern due to limited treatment options. Genotypic investigation of isolates from companion animal origin revealed common human lineages that were further undistinguishable from representative isolates of human origin. Therefore, these animals should be considered as an infection source for humans and vice versa. To reduce the total burden of MRSA in both, human and veterinary medicine, it is necessary to take various epidemiological pathways into account and thus, to strengthen the collaboration between human and veterinary medicine according to the concept of “One Health”.