Objectives: An increase in nosocomial infections caused by ampicillin-resistant Enterococcus faecium (AREfm) has been recently observed in some European countries. Based on multilocus sequence typing (MLST), most hospital AREfm isolates belong to one distinct genogroup, clonal complex 17 (CC17). In this study, we investigated the occurrence of AREfm CC17 in faecal samples collected from healthy dogs in Denmark and in England.

Methods: 210 healthy dogs were screened for the occurrence of AREfm using a selective isolation procedure, i.e. plating on Slanetz Bartley agar containing 32 µg/ml ampicillin. Presumptive AREfm were confirmed by a species-specific PCR and their resistance patterns were determined according to CLSI guidelines. The purK gene was sequenced in all isolates and a subset of 15 isolates was further analysed by MLST analysis.

Results: AREfm was detected in 59 (28%) dogs. Based on MLST or identification of the CC17-specific purK 1 allele, at least 44 (75%) of the isolates belonged to CC17. Four sequence types were observed: ST78 (n=8), ST19 (n=3), ST192 (n=3) and ST266 (n=1). All these genotypes have been previously isolated from hospitalized patients. In particular, ST78 and its single-locus variant ST192 are among the most common STs in European hospitals. ST78 was isolated from a dog and 10-year old boy living in the same household, suggesting possible transmission between dogs and humans living in close contact. Resistance to erythromycin (97%), ciprofloxacin (95%), tetracycline (83%) or rifampicin (56%) was frequent. Only few isolates were resistant to gentamicin (5%), linezolid (14%) and quinopristin/dalfopristin (15%) and all were susceptible to vancomycin.

Conclusion: This is the first report describing the occurrence of AREfm CC17 in dogs. The results suggest that dogs may contribute to the spread of this AREfm genetic lineage in the human population. The unexpected and widespread occurrence of hospital-adapted clones in dogs raises an important question concerning the evolution of this clonal complex: does CC17 originate from humans (anthropozoonosis) or from dogs (zooanthroponosis)? Canine AREfm are currently screened for putative virulence genes (esp, acm, hyl, orf903, orf905, orf907, orf2351 and orf2430) and the results of this screening will be used for discussing the evolutionary relationship between human and canine strains in the conference presentation.