One Health Insights into Enterococcus: Antimicrobial Resistance and Virulence in Companion Animals and Their Tutors

Enterococcus spp. are opportunistic pathogens and commensals in humans and animals and are widely used as indicators of bacterial exchange, providing insights into antimicrobial resistance (AMR) and virulence dissemination within the One Health continuum. Enterococcus from healthy companion animals and their tutors were characterized to compare AMR profiles and virulence traits between hosts and within households in Lisbon, Portugal. Fecal samples (n = 45) were collected from 17 animals and 11 tutors. Enterococci were recovered from selective media, subjected to random amplified polymorphic DNA PCR (RAPD-PCR) and species identification, tested for antimicrobial susceptibility, and screened for virulence traits. Among animal isolates, 61% were Enterococcus faecalis, 29% E. faecium, and 10% E. hirae, whereas human enterococci comprised 52% E. faecalis, 35% E. faecium, 8% E. hirae, and 4% other species. Erythromycin resistance was identical in both groups (29%; Chi-squared test, p = 0.99). Ampicillin resistance was detected in all animal samples but was absent in human samples, whereas tetracycline and rifampicin resistance showed moderate host-specific patterns. Hemolytic activity was detected in 16% of animal and 31% of human isolates, all cylA-positive. Significant associations were observed between host origin and resistance to ampicillin and rifampicin, and between species and resistance to erythromycin and tetracycline. These findings suggest that companion animals can harbor, and potentially disseminate, AMR and virulence traits, reinforcing the need for One Health surveillance.