Comparison of in vitro activity (MIC) of seven antibiotics for exclusive use in humans between Staphylococcus pseudintermedius and Staphylococcus aureus

This study aims to evaluate the activity (MIC) of seven cat. A antibiotics (AMEG classification, EMA 2019) -Ceftaroline, Daptomycin, Linezolid, Quinupristin-Dalfopristin, Teicoplanin, Telavancin, Vancomycin- against S. pseudintermedius; and to compare our results with MIC distributions reported for S. aureus by EUCAST (https://www.eucast.org/mic_distributions_and_ecoffs/). Forty strains were gathered from dogs’ and cats’ clinical samples conferred to the microbiology laboratory of the Turin University Veterinary Hospital during two years (Feb 2019 – Feb 2021). They were identified by MALDI-TOF and PCR (nuc gene). MICs were measured using E-Tests. The distribution of MIC was visually evaluated to identify different populations. Weighted mean of the MIC was compared with the one reported for S. aureus by t-tests, adjusting p-values for multiple tests (q-value). Visually, all strains were deemed as drawn from the same population. The lack of MIC distributions regarding S. pseudintermedius in the EUCAST database prevented us from inferring whether these samples belong or not to the wild-type population. The MICs values of Linezolid, Daptomycin, Telavancin and Vancomycin were higher for S. aureus than S. pseudintermedius (q < 0.01). The MIC of Ceftaroline was higher for S. pseudintermedius than S. aureus (q = 0.008). No difference was observed in the MICs of Quinupristin-Dalfopristin and Teicoplanin. We observed MIC equal or higher than those reported for S. aureus in 3/7 cat. A antibiotics. These findings are less concerning from a veterinarian point of view than from a One-Health perspective, especially in the light of the zoonotic potential of S. pseudintermedius.