Vetnuus | December 2025 9 Note: p-values < 0.05 were considered statistically significant. False discovery rate (FDR)-adjusted q-values were calculated using the Benjamini–Hochberg procedure and are presented for comparisons involving multiple antimicrobial resistance outcomes. The prevalence comparison was not included in the multiple testing correction as it represents a single test; therefore, only the raw p-value is reported for this parameter. Risk difference (RD) and relative risk (RR) are provided with 95% confidence intervals (CI). RD represents the absolute difference in resistance proportions between the two groups, whereas RR reflects the relative likelihood of resistance in isolates from dogs with otitis externa compared to those from clinically healthy dogs. 3. Discussion The prevalence of S. pseudintermedius in this study was 40%, which is consistent with findings reported by Hassan et al. [15] (41.6%) and Penna et al. [16] (38.4%), and somewhat higher than the 31.5% reported by De Martino et al. [17]. These similarities may reflect broadly comparable epidemiological conditions and sampling strategies across studies, such as targeting clinical isolates from companion animals with similar clinical presentations. However, slight differences in prevalence could stem from geographic variability, including differences in population density, pet ownership practices, and local veterinary diagnostic capacities. Moreover, differences in study design, such as sample size or inclusion criteria, could also influence prevalence rates and partially account for the variability observed across studies. AMR profile revealed a predominance of tetracycline resistance (37.5%) (Table 1), consistent with De Martino et al. [17] (35.5%) and Rosales et al. [18] (41.7%). The slightly lower or higher values observed in these studies likely reflect variations in local antimicrobial usage patterns. For example, tetracyclines remain widely used in veterinary medicine due to their broad-spectrum activity and affordability, which may contribute to a sustained selective pressure favouring resistant strains. The even higher resistance rate reported by Tesin et al. [19] (52%) may be influenced by regional overuse or misuse of tetracyclines, as well as the inclusion of isolates from animals with recurrent infections, where resistance is typically higher. Resistance to penicillin was observed in 23.1% of isolates. This rate is considerably lower than the values reported by Bourély et al. [20] (68.5%), Rosales et al. [18] (69%), and Scherer et al. [21] (77.3%), but higher than the 7% reported by Rubin et al. [22]. Several factors may account for these discrepancies. First, methodological differences, such as the antimicrobial susceptibility testing method employed (e.g., disk diffusion vs. MIC determination), the inclusion or exclusion of intermediate isolates, and the interpretive criteria applied (e.g., CLSI vs. CA-SFM), can significantly influence reported resistance rates [22]. Second, the studies differ in the bacterial populations analysed: while our study focused exclusively on S. pseudintermedius, others may have included mixed staphylococcal species or isolates preselected based on methicillin susceptibility, which could introduce selection bias. Third, regional variation in antimicrobial stewardship strategies, veterinary prescribing behaviours, and regulatory frameworks likely contributes to differences in resistance patterns. Given these substantial methodological and epidemiological differences, direct comparisons across studies should be interpreted with caution. Clindamycin resistance was observed in 21.9% of isolates, aligning with Rosales et al. [18] (29.4%) but higher than the 9% reported by Norström et al. [23]. These differences may reflect variation in the therapeutic use of lincosamides across regions. Moreover, Norström et al. [23] isolated S. pseudintermedius from both otic and skin infections, and it is possible that site-specific differences in bacterial populations or exposure to clindamycin contributed to the lower resistance observed. Gentamicin resistance was low (1.3%) in our study, which matches the 1% reported by Bugden [24] and is notably lower than values from De Martino et al. [17] (11.1%), Bourély et al. [20] (13.5%), and Rosales et al. [18] (17.6%). This finding may suggest that aminoglycosides are either used sparingly or mainly in severe infections where culture and sensitivity testing are performed, limiting their contribution to resistance selection. Similarly, erythromycin resistance was very limited (1.3%), in stark contrast to the much higher rates reported by Rosales et al. [18] (29.7%), Bourély et al. [20] (29.8%), and especially Penna et al. [16] (80%). These discrepancies likely reflect regional differences in antimicrobial policies and prescription behaviours, and possibly different exposure histories of the bacterial populations sampled. Trimethoprim-sulfamethoxazole resistance was found in only 3.8% of isolates, consistent with Rubin et al. [22] (5%), but considerably lower than rates reported by Rosales et al. [18] (18%) and De Martino et al. [17] (46.6%). The low resistance rate observed in our study may indicate either limited use of this antibiotic in clinical veterinary practice or its continued efficacy due to stewardship efforts. It is also possible that local veterinary guidelines prioritise other antimicrobials, thus reducing the selective pressure for resistance to this compound. In the present study, the susceptibility of S. pseudintermedius isolates was assessed with respect to several antimicrobials reserved solely for human use. This included linezolid, vancomycin, tigecycline, and teicoplanin—agents classified as important and reserved for the treatment of human infections. Additionally, moxifloxacin, a fluoroquinolone approved for human use, was tested [25]. All isolates were susceptible to antibiotics reserved for human use (linezolid, vancomycin, tigecycline, and teicoplanin), demonstrating 100% susceptibility (n = 160) (Tables 1 and 2). In contrast, a resistance rate of 1.3% (n = 2) was observed for moxifloxacin (Table 1). The monitoring of AMR should extend beyond agents exclusively used in veterinary medicine, given the zoonotic threat posed by MRSP and its capacity to spread AMR genes via horizontal gene transfer [26]. Regarding MDR strains, they were isolated at a rate of 8.7% in this study (Table 3). Our findings differ from those reported by Viegas et al. [11], who documented an MDR prevalence of 14.5% among S. pseudintermedius strains isolated from canine external otitis cases. The proliferation of MDR bacterial strains constitutes a critical threat to global health, as underscored by the World Health Organisation. The rising incidence of infections attributable to MDR organisms, alongside the dwindling efficacy of current therapeutic options, is projected to contribute to increased fatality levels among animal and human hosts affected by such diseases. MDR is generally defined by resistance to antimicrobial agents spanning a minimum of three distinct antimicrobial classes [27]. Regarding the MRSP strains, they were isolated at a rate of 1.2% in this study (Table 3). Leading Article
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