Staphylococcus saprophyticus (S. saprophyticus) is an opportunistic coagulase-negative staphylococcus (CoNS) known to cause urinary tract infections in humans and is increasingly recognized in veterinary medicine. The aim of this study was to provide an epidemiological characterization of S. saprophyticus strains and to identify potential virulence factors that may contribute to interspecies transmission. This research is particularly important, as companion animals represent an understudied reservoir of this microorganism, and their role in the spread of resistant pathogens remains insufficiently understood. A total of 61 S. saprophyticus strains isolated from humans, dogs, and cats were analyzed. Identification was performed using MALDI-TOF MS and confirmed by PCR targeting the hrcA gene. Antimicrobial susceptibility was assessed using the disk diffusion and broth microdilution methods, while resistance genes were detected by PCR. The blaZ and mecA genes were present in all strains; additionally, the majority harbored the resistance genes ermA, ermB, tetM, and tetK. Multidrug resistance (MDR) was identified in 21/61 strains (34.4%). Biofilm-forming capacity was temperature-dependent, with the strongest biofilm production observed at 37 °C (70.5%). At 38 °C and 39 °C, the proportion of strong biofilm producers decreased to 50.8% and 52.5%, respectively. All tested strains demonstrated pathogenic potential in the Galleria mellonella larvae infection model, with the highest mortality recorded for selected feline and canine strains. These findings indicate that S. saprophyticus strains from both humans and companion animals possess notable virulence and multidrug resistance. The detection of genotypically and phenotypically resistant strains in animals highlights their potential role as reservoir for zoonotic transmission.

Introduction: Staphylococci commonly colonise the skin and mucous membranes of humans and animals, the close contact between which may promote interspecies transmission of these microorganisms and determinants of drug resistance. Material and Methods: Material collected from animals (n = 274) and humans (n = 261) between 2019 and 2023 was studied. Samples were swabbed from six anatomical sites of each pet: the external ear canal, conjunctival sacs, nares, oral cavity, groin skin and anus. Swabs were taken from four places of each human: the vestibule of the nasal cavity, the throat near the tonsils, and the skin behind the auricle and in the elbow bend. The pets’ owners and the human participants completed a questionnaire about the study subject and the subject’s living environment to elucidate risk factors associated with staphylococci colonisation. Results: The prevalence of Staphylococcus aureus was 12.42% in cats and 8.85% in dogs, while S. pseudintermedius was isolated from 5.59% of cats and 58.41% of dogs. Of the people, 38.7% were carriers of S. aureus and 2.68% carriers of S. pseudintermedius . A total of 202 S. aureus strains and 165 S. pseudintermedius strains were analysed. Drug resistance was tested in disc diffusion and resistance genes were detected by PCR. The most frequent resistance of S.aureus was to ampicillin (62.4%), penicillin (61.4%) and erythromycin (29.2%), while S. pseudintermedius was mostly resistant to penicillin (71.5%), ampicillin (63.6%) and clindamycin and erythromycin (41.2% in both cases). Methicillin resistance was found in 4.5% of S. aureus and 12.1% of S. pseudintermedius isolates. The most common S. aureus resistance genes were blaZ (79.7%), tet [M] (53.1%) and ermA (29.7%) and the S. pseudintermedius pattern was of blaZ (84.2%), tet [M] (53.3%) and ermB (38.2%). Regarding risk factors, animals from non-commercial sources had 11-fold higher methicillin resistance than those from commercial breeders, dogs had 50-fold lower risk than humans, and recent antibiotic treatment also increased resistance. Conclusion: Monitoring the epidemiology of strains and knowing the prevalence of resistant isolates can shape preventive programmes in both veterinary and human medicine, inform appropriate therapeutic decisions and combat the phenomenon of drug resistance.

Staphylococcus saprophyticus (S. saprophyticus) is an opportunistic coagulase−negative staphylococcus (CoNS) known to cause urinary tract infections in humans and increasingly recognized in veterinary medicine. The aim of this study was to provide an epidemiological characterization of S. saprophyticus strains and to identify potential virulence factors that may contribute to interspecies transmission. This research is particularly important, as companion animals represent an understudied reservoir of this microorganism, and their role in the spread of resistant pathogens remains insufficiently understood. A total of 61 S. saprophyticus strains from humans, dogs and cats were analyzed. Identification was performed using MALDI –TOF MS and confirmed by PCR targetting the hrcA gene. Antimicrobial susceptibility was assessed using disk−diffusion and broth microdilution methods, while resistance genes were detected by PCR. The blaZ and mecA genes was present in all strains; additionally, the majority harbored resistance genes ermA, ermB, tetM, and tetK. Multidrug resistance (MDR) was identify in 21/61 strains (34.4%). Biofilm−forming capacity was temperature−dependent, with the strongest biofilm production observed at 37℃ (70.5%). At 38℃ and 39℃, the proportion of strong biofilm producers decreased to 50.8% and 52.5%, respectively. All testes strains demonstrated pathogenic potential in the Galleria mellonella larvae infection model, with the highest mortality recorded for selected feline and canine strains. These findings indicate that S. saprophyticus strains from both humans and companion animals possess notable virulence and multidrug resistance. The detection of genotypically and phenotypically resistant strains in animals highlights their potential role as reservoir for zoonotic transmission.

Staphylococcus lugdunensis is an opportunistic coagulase-negative Staphylococcus increasingly reported in both humans and companion animals. In this study, we performed a comprehensive characterization of S. lugdunensis isolates obtained from different hosts and clinical backgrounds. Species identification was conducted using MALDI-TOF MS and confirmed by PCR targeting the species-specific fbl gene, complemented by partial rpoB sequencing. The isolates were analysed using multilocus sequence typing (MLST), PCR-based detection of antimicrobial resistance genes, and phenotypic antimicrobial susceptibility testing. Biofilm formation was assessed using a crystal violet microtiter plate assay under different incubation temperatures, and the virulence of selected strains was evaluated using the Galleria mellonella larvae infection model. The isolates exhibited genetic diversity and variable antimicrobial resistance and biofilm phenotypes. Among the analysed isolates, biofilm production was significantly influenced by incubation temperature and host origin, and selected strains caused differential larval survival in the G. mellonella model. Collectively, these findings highlight the heterogeneity of the analysed S. lugdunensis collection comprising human- and animal-derived isolates and support the need for further studies within the One Health framework.

Staphylococcus haemolyticus is an opportunistic coagulase-negative staphylococcus increasingly recognized as an important reservoir of antimicrobial resistance within the One Health framework. However, comparative studies simultaneously evaluating isolates from humans and companion animals remain limited. This study characterized 113 S. haemolyticus isolates recovered from clinically healthy and affected humans and cats and from clinically healthy dogs using phenotypic, molecular, proteomic, and genomic approaches. Multidrug resistance was identified in 45.13% (51/113) of isolates. Whole-genome sequencing of 35 selected isolates revealed substantial genomic diversity, with no clear clustering according to host species or clinical status within the analysed subset. The VFDB-associated loci tufA, clpC, and clpP were detected in all sequenced isolates; however, their presence does not imply expression or a direct contribution to virulence-related phenotypes. Acquired antimicrobial resistance determinants showed variable distributions across the analysed genomes. Within the WGS subset, mecA showed a host-associated difference that remained significant after false discovery rate correction in a one-isolate-per-host sensitivity analysis, whereas the initially observed association for blaZ/PC1-family determinants was not retained after this sensitivity analysis. No acquired resistance determinant was significantly associated with clinical status. Among the full collection of 113 isolates, blaZ (53.98%) and tetL (33.63%) were the most frequently detected resistance genes by PCR. Genotype–phenotype concordance varied according to the antimicrobial agent and phenotypic testing method, indicating that resistance-gene detection alone was not uniformly predictive of phenotypic susceptibility. Biofilm formation, assessed in all 113 isolates, increased markedly at 39 °C despite heterogeneous, strain-dependent changes in planktonic growth. Eight representative isolates evaluated in the Galleria mellonella model showed clear inoculum-dependent and strain-variable larval mortality; however, the assay was not designed to formally assess host-species- or clinical status-associated differences. Overall, the findings demonstrate substantial genomic and phenotypic overlap among human and companion-animal S. haemolyticus isolates, together with selected host-associated differences and marked strain-level variability, supporting the value of integrated One Health surveillance.

Staphylococcus epidermidis is an important opportunistic pathogen and a potential reservoir of antimicrobial resistance determinants, yet comparatively little is known about isolates originating from both humans and companion animals. This study characterized 320 S. epidermidis isolates obtained from humans, cats, and dogs within a One Health framework using phenotypic, molecular, proteomic, and genomic approaches. Antimicrobial susceptibility testing revealed high frequencies of resistance to oxacillin (67.19%), erythromycin (66.56%), tetracycline (55.63%), and clindamycin (53.75%) by disk diffusion. PCR-based analysis identified blaZ as the most prevalent resistance determinant (50.63%), whereas whole-genome sequencing of a selected subset revealed a broader and heterogeneous repertoire of resistance-associated genes. Among 67 sequenced isolates, 26 known sequence types were identified, including several STs occurring in isolates from more than one host species. Core-genome phylogenetic analysis demonstrated substantial genomic diversity without complete segregation according to host species or clinical status. Genotype–phenotype concordance was generally limited and gene dependent, and discrepancies were also observed between PCR- and WGS-based detection for selected resistance determinants. Biofilm formation was significantly influenced by incubation temperature, host species, and clinical status, while growth kinetics showed pronounced strain-specific variability and no consistent relationship with biofilm-forming capacity. MALDI-TOF MS profiling and partial rpoB phylogeny likewise showed considerable overlap among isolates from different host groups. In the Galleria mellonella infection model, mortality was inoculum dependent and varied substantially among strains. Overall, the findings demonstrate marked phenotypic and genomic heterogeneity among S. epidermidis isolated from humans and companion animals and indicate that some clonal backgrounds and resistance determinants occur across host species, highlighting the relevance of this species within a One Health context.