Vetnews | Desember 2025 6 « BACK TO CONTENTS Antimicrobial Resistance Profile of Staphylococcus pseudintermedius Isolated from Dogs with Otitis Externa and Healthy Dogs: Veterinary and Zoonotic Implications Ionela Popa 1, Ionica Iancu 2*, Vlad Iorgoni 2, Janos Degi 2, Alexandru Gligor 2, Kalman Imre 3, Emil Tîrziu 4, Timea Bochis1, Călin Pop1, Ana-Maria Plotuna5, Paula Nistor 2, Marius Pentea 6, Viorel Herman 2 and Ileana Nichita 4 1 Department of Semiology, Faculty of Veterinary Medicine, University of Life Sciences “King Mihai I”, 300645 Timisoara, Romania; ionela.popa@usvt.ro (I.P.); timea. bochis@usvt.ro (T.B.); calinpop@usvt.ro (C.P.) 2 Department of Infectious Diseases and Preventive Medicine, Faculty of Veterinary Medicine, University of Life Sciences “King Mihai I”, 300645 Timisoara, Romania; vlad. iorgoni@usvt.ro (V.I.); janosdegi@usvt.ro (J.D.); alexandru.gligor@usvt.ro (A.G.); paula.nistor@usvt.ro (P.N.); viorel.herman@fmvt.ro (V.H.) 3 Department of Food Safety and Hygiene, Faculty of Veterinary Medicine, University of Life Sciences “King Mihai I”, 300645 Timisoara, Romania; almanimre@usvt.ro 4 Department of Microbiology, Faculty of Veterinary Medicine, University of Life Sciences “King Mihai I”, 300645 Timisoara, Romania; emiltirziu@usvt.ro (E.T.) 5 Department of Animal Nutrition, University of Life Sciences “King Mihai I”, 300645 Timisoara, Romania; anamaria.plotuna@usvt.ro 6 Department of Anatomy, University of Life Sciences “King Mihai I”, 300645 Timisoara, Romania; mariuspentea@usvt.ro * Correspondence: ionica.iancu@usvt.ro Abstract Background/Objectives: Staphylococcus pseudintermedius (S. pseudintermedius) is an opportunistic pathogen frequently isolated from dogs, involved in a wide range of infections, particularly otitis externa. Increasing antimicrobial resistance (AMR), including methicillin-resistant S. pseudintermedius (MRSP), poses significant challenges for veterinary and potentially human health. This study aimed to assess the prevalence and antimicrobial resistance profiles of S. pseudintermedius in dogs with otitis externa compared to clinically healthy dogs. Methods: Between 2022 and 2025, samples were collected from 400 dogs with otitis externa and 360 healthy dogs in veterinary clinics from Timis, oara. Ear swabs were processed by conventional microbiological techniques and confirmed using MALDI-TOF MS. Antimicrobial susceptibility was tested using the VITEK® 2 Compact system, following CLSI VET01, Fifth Edition (2018) standards. Fourteen antimicrobials from 11 classes were evaluated. Results: S. pseudintermedius was isolated in 40% of dogs with otitis externa and in 21.1% of healthy dogs. The highest resistance in both groups was observed to tetracycline (37.5% and 25%, respectively). No resistance was recorded to linezolid, vancomycin, teicoplanin, tigecycline, or fusidic acid. MRSP strains were identified in 1.2% of dogs with otitis, displaying multidrug resistance (MDR). MDR strains were also detected in 8.7% of diseased and 4% of healthy dogs, indicating the potential for subclinical reservoirs. Conclusions: The findings highlight the notable prevalence and AMR of S. pseudintermedius in both symptomatic and asymptomatic dogs. The detection of MRSP and MDR strains emphasises the need for prudent antibiotic use and continuous AMR surveillance in veterinary medicine to mitigate zoonotic risks and preserve antimicrobial efficacy. 1. Introduction S. pseudintermedius, an opportunistic pathogen, is commonly isolated from clinically healthy dogs and is notably involved in a wide spectrum of animal infections [1]. This bacterium can colonise between 46% and 92% of healthy dogs [2]. S. pseudintermedius is recognised as a key pathogen in dogs, has also occasionally been linked to cases of human infection [3,4], while it also plays a significant role in infections among cats [4]. The growing identification of S. pseudintermedius isolated from canine cases of otitis externa and soft tissue or skin infections represents a rising concern in the veterinary field, primarily due to its considerable resistance to antimicrobials and a broad range of virulence factors [5]. Antimicrobial resistance (AMR) has become a major global health issue, widely recognised as one of the most critical threats of this century, with implications for both human and animal health [6–9]. In recent years, there has been an observed increase in the frequency of methicillin-resistant S. pseudintermedius (MRSP) strains, both in sick dogs and in clinically healthy ones [10]. The spread of MRSP has come to represent a major issue in veterinary practice [11]. MRSP resistance is determined by the presence of the mecA gene, integrated into a mobile genetic element known as the staphylococcal chromosomal cassette mec (SCCmec). This gene confers resistance to most beta-lactam antibiotics, except for ceftaroline and ceftobiprole, which are part of the fifth generation of cephalosporins [11,12]. The mecA gene encodes a structurally altered penicillin-binding protein with low affinity for nearly all beta-lactam antibiotics [10,13]. Consequently, these antibiotics no longer represent a barrier to bacterial cell wall synthesis, unlike under normal circumstances when beta-lactams bind to the penicillin-binding protein and thereby inhibit the bacterium’s ability to construct its cell wall [13]. In addition, the SCCmec acquired by MRSP is a mobile genetic element [10–13] that may also carry other resistance genes, contributing, along with other mobile genetic elements, to multidrug resistance patterns (MDR) [12]. Resistance of MRSP strains has also often been observed within other classes of antimicrobials, namely: aminoglycosides, fluoroquinolones, macrolides [11,12], trimethoprim–sulfamethoxazole, lincosamides, tetracyclines, and chloramphenicol [12]. S. pseudintermedius can be transmitted to humans, particularly those in close contact with dogs, potentially causing zoonotic infections such as abscesses, infected bite wounds, pneumonia, bloodstream infections, and septic arthritis [10]. Consequently, MRSP has become an increasingly significant concern in veterinary as well as human medicine, due to the limited treatment options available [14].
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