ABSTRACT
Background
Otitis externa (OE) represents a common clinical problem in dogs. Allergic dogs exhibit reduced diversity of the otic microbiota, and inflammation‐induced changes in the ear canal microenvironment result in a further decline in microbial biodiversity. Probiotics have demonstrated efficacy in certain dermatological conditions, including atopic dermatitis, which is, in turn, the leading primary cause of OE in dogs.
Objectives
To evaluate the efficacy of probiotic‐based ear drops in controlling clinical signs related to erythroceruminous non‐infected OE in dogs.
Animals
Thirty‐seven privately owned dogs with non‐infected OE.
Materials and Methods
Dogs received probiotic‐based ear drops topically every 48 h for 28 days, in accordance with the manufacturer's instructions. Assessments were performed at enrolment (Day [D]0), D14 and D28, including cytological evaluation of ear discharge, pruritus intensity (PVAS, pruritis Visual Analogue Scale), severity of otic lesions (OTIS3, 0–3 Otitis Index Score) and a quality‐of‐life survey (QoL).
Results
At enrolment (D0), mean OTIS3 and PVAS scores for all included animals were 5.11 ± 1.20 and 4.93 ± 1.51, respectively. Both scores decreased significantly by D28, to 1.66 ± 1.75 and 2.09 ± 2.03, respectively. Clinical improvement was evident regardless of concomitant medication use or the type of micro‐organism's overgrowth observed during the initial cytological assessment. Owner‐reported QoL improved in 80% of the dogs.
Conclusion and Clinical Relevance
These probiotic‐based ear drops may be a useful adjunctive therapy in cases of canine non‐infectious erythroceruminous OE.
Keywords: dogs, lactobacilli, otitis externa, probiotherapy, probiotics
Background: Otitis externa (OE) represents a common clinical problem in dogs. Allergic dogs exhibit reduced diversity of the otic microbiota, and inflammation‐induced changes in the ear canal microenvironment result in a further decline in microbial biodiversity. Probiotics have demonstrated efficacy in certain dermatological conditions, including atopic dermatitis, which is, in turn, the leading primary cause of OE in dogs. Objectives: To evaluate the efficacy of probiotic‐based ear drops in controlling clinical signs related to erythroceruminous non‐infected OE in dogs. Conclusion and Clinical Relevance: These probiotic‐based ear drops may be a useful adjunctive therapy in cases of canine non‐infectious erythroceruminous OE.
1. Introduction
Otitis externa (OE) is a common clinical condition in dogs [1, 2], characterised by inflammation of the external ear canal and pinna, often accompanied by secondary bacterial or yeast infections or microbial overgrowth [3]. It often progresses to a chronic and recurrent condition, substantially impairing the quality‐of‐life (QoL) of both the affected dogs and their caregivers [4], and constitutes a leading cause of repeated antibiotic administration in canine patients [5].
Among others, allergic dermatoses are one of the most frequent primary causes of OE in dogs [3, 6], with erythroceruminous OE being the most common clinical presentation.
As with cutaneous microbiota elsewhere [7, 8], otic microbiota is highly rich and diverse under physiological conditions. In allergic dogs, inflammation of the skin of the ear canal alters the physicochemical properties of the auricular microenvironment, leading to a loss in microbial biodiversity (dysbiosis) [9]. Interestingly, these changes in ear microbiota are observed before clinical signs of otitis develop, with increased abundance of opportunistic pathogens such as Staphylococcus spp. and Pseudomonas spp., and a reduction of other micro‐organisms essential for cutaneous homeostasis, such as Lactobacillus spp. [10, 11, 12] These alterations further disrupt skin barrier function and immune responses, promoting progression to chronic inflammation and infection [3], in a vicious circle. Therefore, it is reasonable to speculate that primary alterations in microbiota diversity may be implicated in the pathophysiology of OE in dogs and in the progression of clinical signs.
Long‐term management of allergic OE focuses on controlling the underlying inflammation [3, 13], which reduces, in turn, the occurrence of secondary infections and the need for antimicrobials [14]. Probiotics, defined as live micro‐organisms conferring health benefits to the host when administered in adequate amounts, have demonstrated utility in managing cutaneous disorders in humans and dogs [15, 16, 17]. Their effects depend on the selected strain and the formulation used. Among these, Lactobacillus spp. is supported by strong evidence in human medicine, particularly for their immunomodulatory properties and beneficial impact on pathogen control [18, 19, 20, 21, 22, 23, 24]. Considering the dysbiosis observed in dogs affected by OE, maintaining microbiota diversity and promoting beneficial bacteria such as Lactobacillus spp. may improve primary clinical signs and reduce the incidence of secondary infections.
ProAuris is a probiotic‐based product for ear application containing > 10 [8] colony‐forming unit (cfu)/mL of Lactiplantibacillus plantarum YUN‐V2.0 and Lacticaseibacillus rhamnosus YUN‐S1.0 (species previously assigned to the Lactobacillus genus) together with caprylic/capric triglycerides and silicon dioxide. The combination of these ingredients is designed to support the recovery of a healthy ear microbiome and is indicated for dogs with susceptible ears and microbiome rebalance in the event of dysbiosis or following antimicrobial treatment.
The aim of this study was to evaluate the effects of a probiotic suspension in drops containing Lactiplantibacillus plantarum YUN‐V2.0 and Lacticaseibacillus rhamnosus YUN‐S1.0 on controlling clinical signs and typical otic pathological findings associated with canine erythroceruminous OE. This was evaluated in animals receiving the probiotic‐based ear drops (from now PED) only and in animals facing a flare‐up even when under a treatment protocol in place for the management of erythroceruminous OE.
2. Materials and Methods
2.1. Ethics
As a field trial performed with a marketed non‐medicinal product no ethical approval was required by the regulatory authorities. However, the study was performed following the product labelling indication for use and assuring all national regulatory and animal welfare standards and requirements were satisfied. All dog owners signed a consent form and could withdraw their dogs from the study at any time.
2.2. Study Design
Prospective, multicentre, open‐label clinical case study.
2.3. Animals
Animals were recruited from veterinary practices located in Spain and Italy. At each veterinary practice, a single clinician with expertise in dermatology was responsible for animal recruitment and evaluations. Dogs of different ages, weights, any breed and both sexes could be enrolled in the study. Dogs were considered eligible for the study if they were diagnosed with mild‐to‐moderate non‐infectious canine recurrent erythroceruminous OE and met all the inclusion and exclusion criteria described in Table 1.
TABLE 1.
Inclusion and exclusion criteria of client‐owned dogs suffering from erythroceruminous otitis externa (OE) for participation in the study.
| Inclusion criteria | Exclusion criteria |
|---|---|
| Client‐owned dogs presenting at the veterinary practice with signs of mild‐to‐moderate non‐infectious canine recurrent erythroceruminous chronic (> 3 months) OE in at least one eara. | Dogs with parasitic ear disease. |
| Dogs presenting with an OTIS3 ≥ 4b. | Dogs with infectious ear disease. |
| Dogs could be under a treatment protocol for the management of OE yet this protocol could not be changed throughout the study. | Dogs with underlying systemic disease that could affect study outcomes. |
| If exudate was present it had to be non‐suppurative. | Dogs that had received topical probiotics for the last month. |
|
Cytological examination demonstrated absence of infection (no PMNs present). |
Dogs that had received topical products with antiseptic activity for the last 2 weeks. |
| Cytological examination demonstrated the presence of > 25 cocci (×1,000) and a maximum of 4–6 Malassezia per field (×400). | Animals exhibiting aggressive or frightened behaviour that causes difficulty in clinical examinations. |
| The dog had been on an ectoparasite control regime for ≥ 3 monthsc. | Animals participating in another study |
Abbreviation: OTIS3, 0–3 Otitis Index Score.
In case of bilateral OE both ears were treated but only the ear in the worse condition on Day 0 was considered in the evaluation.
Single ear canal score (one score incorporating the assessment of both the vertical and horizontal ear canals).
The protocol could not be changed throughout the study.
In order to confirm the absence of active infection, cytological evaluation was performed by collecting samples from the ear canals and preparing thin smears on glass slides. Cytological preparations were air‐dried before staining using a modified Wright–Giemsa stain. They were then rinsed with water, allowed to dry, and five random fields were inspected. The criterion used to differentiate between microbial overgrowth and infection was the absence or concomitant presence of neutrophils, respectively, and therefore the presence of intracellular bacteria. Bacterial overgrowth was considered to be present when > 25 cocci per high‐powered field (hpf) (×1000) were observed. Regarding the bacterial type, because this was solely a phenotypic assessment based on microscopic observation rather than microbiological culture, only animals in which cocci were observed on cytological evaluation were included; cases with bacilli were excluded in all instances. Regarding yeasts, overgrowth was defined as the presence of > 4–6 organisms per hpf (×400 magnification).
Concomitant treatment with systemic or topical products with antiseptic activity was not permitted throughout the study. Dogs that were already receiving treatment (topical or systemically) for OE and whose clinical signs were not adequately controlled by that therapy could be included in the study. Their ongoing treatment—always consisting of non‐antimicrobial medications as described in the exclusion criteria—remained unchanged, except for the addition of the topical probiotic under investigation. Ear cleaners with no antiseptic activity were permitted if they had been in use before study enrolment and were always to be administered ≥ 4 h before the probiotic application to avoid potential interactions.
Any dog could be withdrawn from the study in case of occurrence of an adverse event (AE) that required stopping product administration or which could interfere with the evaluation of the study results; an unsatisfactory response that required any modification of the treatment management protocol; presence of ear purulent discharge indicative of infection; a major protocol deviation; treatment compliance difficulties; or withdrawal of the owners' consent. Product application was to be stopped at the time of withdrawal, and no further assessments were to be performed.
2.4. Product Administration
Day (D)0 was defined as the day of inclusion and product administration starting day. Once enrolled, therapy with the PED (proAuris; Ecuphar/Animalcare group) was started, given either alone or in combination with the medications they were receiving according to the treatment management they were already on. Clinicians were responsible for dispensing the study product as well as product accountability. Owners were responsible for product application at home.
The PED were administered topically every 48 h following label instructions for a period of 28 days. Three to six drops were placed at the opening of the ear canal, and the ear was thoroughly massaged to distribute the product properly. Owners were asked to register the product administration daily and record the ease of application.
2.5. Efficacy Assessment
At each veterinary practice a single clinician was responsible for all efficacy assessments. On D0 the clinician recorded all medications which the dogs received, and both ears were clinically assessed and scored for signs associated with erythroceruminous OE. Clinical assessments were repeated on D14 and D28. Cytological evaluation also was performed on D14 and D28 to assess the evolution of the otitis and detect infectious changes that had appeared during treatment. The 0–3 Otitis Index Score (OTIS3) scale [25] was used to assess the severity of the otitis and to evaluate the response to therapy. Four parameters (erythema, oedema/swelling, erosion/ulceration and exudate) were evaluated, as shown in Table S1 of the Supporting Information. The level of otic pruritus was assessed at each study visit by the owners, in the presence of the clinician, by crossing a 0–10 pruritus Visual Analogue Scale (PVAS) [26], where 0 corresponded to no itch and 10 to severe itch. At each visit pictures of the affected ear were taken, and the owners assessed any perceived change of their dog's QoL as better, the same or worse compared to the initial visit on D0, using an ad hoc questionnaire developed for this study, rather than a validated instrument.
2.6. Safety Assessment
Safety was assessed by recording any AE reported irrespective of its nature and severity or whether to be product‐related or not. Owners were informed about the possible AEs related to the product and were instructed to observe the dogs daily and immediately report any suspected AE to the clinician. The safety criteria included the clinical signs and the severity (mild, moderate, severe and life‐threatening) of the reported AEs and incidence calculations. Causality assessment was performed (i.e., probable, possible, unlikely or unknown related to treatment) following the ABON System of causality assessment [27]. For incidence calculation, when several AEs were observed in a single animal at an overlapped time frame, according to current guidelines, they were considered different clinical signs of the same AE. Owing to the topical application of the product, safety assessments were focussed mainly on possible skin reactions on the ear.
2.7. Statistical Analysis
The statistical analyses were performed with the software centurion 18 v18.1.16 (Statgraphics).
Comparisons between values on D14 and D28 with respect to baseline values on D0 were performed for the OTIS3 and the PVAS scores using the nonparametric one‐tailed Wilcoxon signed‐rank test. Data analysis was performed in three parts: (i) comparisons using all included animals; (ii) comparison for animals receiving PED only; and (iii) comparisons for animals receiving PED and other concomitant treatments. Moreover, comparisons between animals receiving PED only and the animals receiving PED and other concomitant treatments also were performed using the nonparametric two‐tailed Wilcoxon–Mann–Whitney U test. The PVAS and the OTIS3 scores also were compared at each time point to determine whether differences could be detected between groups. Baseline values also were compared to confirm that no differences were already detected at baseline. All statistical tests were performed at an overall 5% (p < 0.05) level of significance. A descriptive analysis of the QoL assessed by the owners also was performed. For the analysis of safety parameters all enrolled animals that received at least one dose of the product were included.
3. Results
3.1. Study Population
Thirty‐seven dogs, 20 females (16 spayed, four entire) and 17 males (six neutered, 11 entire) were enrolled in the study. The mean age of the dogs included in the study was 7 years (range 3–15 years). Mean body weight was 21.8 kg (range 2.7–52 kg).
Twenty‐two breeds were represented in this study, in addition to five mixed‐breed dogs. The most represented breeds were Labrador retriever (n = 4), Spanish waterdog (n = 3), poodle (n = 3), Yorkshire terrier (n = 2), German shepherd dog (n = 2), golden retriever (n = 2), French bulldog (n = 2), pug (n = 2) and one dog each for the following breeds: American Staffordshire terrier, Carlino, cocker spaniel, American cocker, husky, Jack Russell terrier, pinscher, shiba inu, shih tzu, Teckel, Terranova and West Highland white terrier.
All dogs presented with non‐infectious canine erythroceruminous OE, and during the cytological assessment, no micro‐organisms were observed in 15 dogs; yeast overgrowth, bacterial overgrowth and mixed population overgrowth (bacteria and yeasts) were observed in 10, 8 and 4 dogs, respectively (Table 2).
TABLE 2.
Mean values of 0–3 Otitis Index Score (OTIS3) and pruritus Visual Analogue Scale (PVAS) score observed on Day (D)0 and D28 in the different micro‐organism's overgrowth observed on cytological results at inclusion on D0.
| Micro‐organism overgrowth | N | D0 | D28 | ||
|---|---|---|---|---|---|
| OTIS3 | PVAS | OTIS3 | PVAS | ||
| No overgrowth | 15 | 4.87 | 4.67 | 1.00 | 0.93 |
| Yeast overgrowth | 10 | 4.60 | 5.15 | 1.90 | 2.60 |
| Bacterial overgrowth | 8 | 5.75 | 5.13 | 1.88 | 3.25 |
| Mixed overgrowth* | 4 | 6.00 | 5.00 | 2.25 | 1.75 |
Abbreviation: N, number of animals.
Bacterial and yeast overgrowth.
Fourteen dogs received PED as the only therapy, and 23 received PED concomitantly with other medications (PED+) for the management of erythroceruminous OE, as part of a systemic picture of atopic dermatitis. The main medications administered concomitantly with PED were oclacitinib (n = 16), lokivetmab (n = 6), oral corticosteroids (n = 4), ciclosporin (n = 2) and allergen‐specific immunotherapy (ASIT, n = 2). Topical corticosteroids (hydrocortisone aceponate) were used in five cases and ear cleaners in 11 cases.
3.2. Efficacy Evaluation
At the initial visit on D0 and before the start of PED application, the mean score on the OTIS3 scale was: for all included dogs 5.11 ± 1.20 (median 5, range 4–9); for dogs receiving PED 5.14 ± 1.17 (median 5, range 4–7); and for those receiving PED+ 5.09 ± 1.24 (median 5, range 4–9). For the PVAS scores, baseline values were: all included dogs 4.93 ± 1.51 (median 5, range 2–8); PED only dogs 4.89 ± 1.50 (median 5, range 2–8); and PED+ dogs 4.96 ± 1.55 (median 5, range 2–8). The OTIS3 and PVAS values were similar regardless of the type of micro‐organism overgrowth observed at inclusion (Table 2).
After application of PED, the mean values for the OTIS3 and the PVAS scores decreased on D14 and D28 compared to D0. On D14, values for the OTIS3 scale were 2.87 ± 2.00 (median 2, range 0–8) for all included dogs; 2.36 ± 1.91 (median 2, range 0–6) for the dogs receiving PED only; and 3.17 ± 2.04 (median 3, range 0–8) for the dogs receiving PED+. On D28, values were 1.66 ± 1.75 (median 1, range 0–8) for all included dogs; 1.71 ± 2.05 (median 1, range 0–8) for PED only dogs; and 1.62 ± 1.56 (median 1, range 0–5) for PED+ dogs. The PVAS scores on D14 were 3.15 ± 1.78 (median 3.5, range 0–6) for all included dogs; 2.82 ± 1.98 (median 3.75, range 0–6) for PED only dogs; and 3.35 ± 1.67 (median 3, range 0–6) for PED+ dogs. On D28, values were 2.09 ± 2.03 (median 2, range 0–7) for all included dogs; 2.21 ± 2.30 (median 2, range 0–7) for PED only dogs; and 2 ± 1.90 (median 2, range 0–6) for PED+ dogs (Figures 1 and 2). From a clinical standpoint, this decrease in OTIS translates into a clear reduction of inflammation and erythema at the macroscopic level (Figure 3).
FIGURE 1.
Box‐and‐Whiskers plot representing evolution of the 0–3 Otitis Index Score (OTIS3) throughout the study in the dogs receiving the probiotic‐based ear drops (PED) only and the dogs receiving the probiotic‐based ear drops and concomitant medications (PED+). Black lines represent mean and crosses represents median values at each time point. Whiskers extend to show the range of scores, and any outliers are marked as individual points.
FIGURE 2.
Box‐and‐Whiskers plot of the pruritus Visual Analogue Scale (VAS) throughout the study in the dogs receiving the probiotic‐based ear drops (PED) only and the dogs receiving the probiotic‐based ear drops and concomitant medications (PED+).
FIGURE 3.
Two dogs included in the study treated with probiotic‐based ear drops (PED) alone. (a) Case 5: erythroceruminous otitis externa (OE) with secondary bacterial overgrowth. (b) Case 6: erythroceruminous OE with secondary overgrowth of Malassezia spp. Day (D) 0: marked erythema, oedema and moderate lichenification evident on the concave surface of the pinna and ear canal. D14 and D28: progressive clinical improvement observed macroscopically following application of PED every 48 h for 14 and 28 days, respectively.
The statistical analysis, when comparing the population medians on D14 and D28 versus D0 for the OTIS3 and the PVAS scores considering all included dogs, or separately dogs receiving PED only, or PED+, revealed statistically significant differences in all cases (Table 3). Additionally, when comparing the dogs receiving PED only versus the dogs receiving PED+ at each time point, no statistically significant differences were detected between groups for OTIS3 and PVAS scores at any time point (Table 4). The differences observed in OTIS3 and PVAS scores between D0 and D28 were similar regardless of the type of micro‐organism's overgrowth observed during the initial cytological assessment (Table 2).
TABLE 3.
Comparisons of the population medians of the 0–3 Otitis Index Score (OTIS3) and the pruritus Visual Analogue Scale (PVAS) scores observed on Day (D)14 and D28 versus D0 in all included dogs and in the dogs receiving the probiotic‐based ear drops only (PED) or the probiotic‐based ear drops and concomitant medications (PED+).
| Differences | N | Median | Q1 First quartile | Q3 Third quartile | p |
|---|---|---|---|---|---|
| All included animals | |||||
| OTIS3_D0–OTIS3_D14 | 37 | 2 | 1 | 3 | < 0.001 |
| PVAS_D0–PVAS_D14 | 2 | 1 | 3 | < 0.001 | |
| OTIS3_D0–OTIS3_D28 | 35 | 4 | 3 | 5 | < 0.001 |
| PVAS_D0–PVAS_D28 | 3 | 2 | 4 | < 0.001 | |
| PED‐treated animals | |||||
| OTIS3_D0–OTIS3_D14 | 14 | 3 | 2 | 4 | 0.001 |
| PVAS_D0–PVAS_D14 | 2 | 1 | 3 | 0.002 | |
| OTIS3_D0–OTIS3_D28 | 14 | 3.5 | 3 | 5 | < 0.001 |
| PVAS_D0–PVAS_D28 | 3 | 2.5 | 4 | 0.002 | |
| PED+‐treated animals | |||||
| OTIS3_D0–OTIS3_D14 | 23 | 2 | 1 | 3 | < 0.001 |
| PVAS_D0–PVAS_D14 | 2 | 1 | 3 | 0.001 | |
| OTIS3_D0–OTIS3_D28 | 21 | 4 | 3 | 4 | < 0.001 |
| PVAS_D0–PVAS_D28 | 3 | 2 | 4 | < 0.001 | |
Abbreviation: N, number of animals.
TABLE 4.
Comparisons at each time point (D, Day) between the population medians of the 0–3 Otitis Index Score (OTIS3) and the pruritus Visual Analogue Scale (PVAS) scores observed in the dogs receiving the probiotic‐based ear drops only (PED) and the dogs receiving the probiotic‐based ear drops and concomitant medications (PED+).
| Time | PED | PED+ | p | ||
|---|---|---|---|---|---|
| N | Median | N | Median | ||
| OTIS3 | |||||
| D0 | 14 | 5 | 23 | 5 | 0.805 |
| D14 | 14 | 2 | 23 | 3 | 0.191 |
| D28 | 14 | 1 | 21 | 1 | 0.861 |
| PVAS | |||||
| D0 | 14 | 5 | 23 | 5 | 0.885 |
| D14 | 14 | 3.75 | 23 | 3 | 0.514 |
| D28 | 14 | 2 | 21 | 2 | 0.917 |
Abbreviation: N, number of animals.
The QoL of the dogs at the end of the study as assessed by owners had improved in 80% of the cases regardless of receiving PED only or PED+. Improvement was achieved more rapidly by D14 in the dogs receiving PED only (Figure S1).
According to the owners, the PED was easy to apply, with most owners reporting that the application was easy or very easy, and the product was well tolerated by the dogs. In most cases, after application, the product was rapidly absorbed, leaving no odour or staining on the skin. Some owners even reported a pleasant odour.
3.3. Safety Evaluation
No adverse events were reported throughout the study in association with topical application of PED.
4. Discussion
To the best of the authors' knowledge, this is the first prospective study to evaluate the effect of topical probiotics on clinical outcomes of erythroceruminous OE. Based on the results obtained, the probiotic‐based ear drops (proAuris) were effective in supporting the control of clinical signs in the dogs included in this study. Clinical improvement was observed early, with significant reductions in both OTIS3 and PVAS scores as early as 14 days after initiating therapy, despite administration every 48 h. Notably, inflammation was controlled in many cases without the use of anti‐inflammatory drugs, which are typically considered a cornerstone in OE management. Furthermore, the degree of clinical improvement did not appear to differ according to the type of micro‐organism overgrowth identified at enrolment, suggesting that the product may be broadly applicable in non‐infected OE cases.
No dogs were withdrawn as a consequence of local adverse effects, and owner‐reported outcomes were favourable, with most describing the ear canal appearance as normal and the product odour pleasant. These aspects are likely to positively influence treatment adherence, which is a key factor in the successful management of OE.
Otitis externa is a common, multifactorial condition in dogs, with primary factors including allergic dermatitis, as well as foreign bodies and ectoparasites, which alter the auditory canal microenvironment [2, 3, 6]. These alterations promote dysbiosis and secondary infections [28, 29, 30], making OE one of the most frequent indications for antimicrobial use in veterinary dermatology [5], and contributing to the development of bacterial resistance [31, 32, 33, 34].
Advances in molecular techniques, particularly 16S rRNA gene sequencing, have significantly improved our understanding of the canine skin microbiota. Rodrigues‐Hoffman [7] reported that approximately 85% of bacteria present on healthy canine skin belong to the phyla Proteobacteria, Actinobacteria, Bacteroidetes, Fusobacteria and Firmicutes. Subsequent studies using next‐generation sequencing have provided a more detailed characterisation of these communities, identifying not only staphylococci but also substantial populations of Lactobacillus spp. within the Firmicutes [35].
Likewise, the microbiota of the healthy canine ear canal has been shown to be more complex than appreciated previously [10, 11, 29]. Leonard et al. [36] identified Firmicutes, Proteobacteria and Actinobacteria as the predominant phyla, with Lactobacillus spp. being particularly abundant. These microbial communities exist in a dynamic symbiotic relationship with the host, mediated by complex immunological and biochemical interactions [37]. The microbiota contributes to cutaneous homeostasis through multiple mechanisms, including promotion of keratinocyte differentiation, regulation of desquamation, maintenance of optimal pH and inhibition of pathogen colonisation [38, 39, 40, 41]. Additionally, it plays a crucial role in immune modulation, including the induction of regulatory T cells and the production of antimicrobial molecules, thereby limiting bacterial overgrowth and biofilm formation [38, 42].
There is increasing evidence supporting the role of microbiota dysbiosis in dermatological diseases in both humans and dogs [9, 30, 43, 44, 45]. Reduced microbiota diversity has been described in allergic dogs, even before the onset of clinical signs [9, 11], whereas established otitis is associated with a shift towards opportunistic pathogens such as Staphylococcus spp. and Pseudomonas spp. [29, 46] These findings highlight the importance of microbiota balance in maintaining ear health and provide a rationale for therapeutic strategies aimed at its modulation.
In this context, probiotics—defined as live micro‐organisms that confer a health benefit to the host when administered in adequate amounts [47]—have emerged as a promising therapeutic approach. Lactobacillus spp., as a fundamental component of the normal cutaneous microbiota, are among the most widely studied probiotic organisms, with evidence supporting their immunomodulatory properties and their capacity to inhibit pathogenic micro‐organisms [19, 20, 21, 22, 23, 24, 48]. The formulation evaluated in this study contains high concentrations of Lactiplantibacillus plantarum YUN‐V2.0 and Lacticaseibacillus rhamnosus YUN‐S1.0, which may contribute to restoring microbial balance and modulating inflammation.
In the present study, the PED also appeared to effectively control otic inflammation. Although part of the observed benefits could theoretically be attributed to the vehicle, which may provide hydration and support barrier function, similar effects would be expected from other commercially available ear cleaners previously used on most dogs included in the study. However, this was not observed, and clinical improvement became evident only after the introduction of the probiotic formulation. Notably, no changes were made to the ongoing treatment in any case, apart from the addition of the probiotic drops.
Other components, such as silicon dioxide, also may contribute to the observed effects through exfoliative or anti‐inflammatory properties [49]. A study design including a vehicle control group would be required to further investigate this possibility. Nevertheless, the primary objective of this study was to evaluate the clinical performance of the final formulation, rather than its individual components.
Some potential confounding factors should be considered. The intermittent nature of OE may lead to spontaneous clinical improvement; however, given the short duration of the study, this is unlikely to fully account for the observed changes. Additionally, although other topical or systemic therapies for OE or the underlying allergic dermatitis were permitted, it was a strict requirement that these treatments remained unchanged throughout the study period. Therefore, although causality cannot be definitively established, the observed improvements are likely to be associated with the addition of the probiotic drops. Nonetheless, given that only mild‐to‐moderate cases were included, a degree of spontaneous improvement cannot be completely excluded.
This study has some limitations. The absence of a control group limits the ability to draw definitive conclusions regarding treatment efficacy. A within‐subject design, such as treating only one ear in dogs with bilateral OE, could have reduced variability associated with underlying disease. Additionally, the open‐label design represents a potential source of observer bias, which may have influenced the results.
Another limitation is the lack of microbiota analysis before and after treatment, which would have allowed correlation between clinical improvement and microbial changes. Although this was beyond the scope of the present study, ongoing research is expected to provide further insights into the effects of the probiotic therapy on the canine otic microbiota. An additional limitation of the study is that a validated QoL questionnaire was not used. However, this was beyond the scope of the present study, as the primary objective was to capture the owner's perception of changes in their pet's QoL in a simple and practical manner. Although this approach may be less robust than the use of validated instruments, it reflects real‐world clinical settings and provides meaningful insight into owner‐perceived outcomes.
Despite being an uncontrolled open‐label, non‐randomised study, the probiotic‐based ear drops (proAuris) resulted in clinically relevant improvement within a short period. Given its good tolerability and ease of application, this product may represent a useful addition to the therapeutic options for the management of canine OE, particularly in mild‐to‐moderate erythroceruminous cases. Future double‐blind placebo‐controlled studies including larger populations and longer follow‐up periods are warranted to determine their long‐term efficacy and to evaluate their potential as an antibiotic‐sparing strategy through modulation of the otic microbiota.
Author Contributions
Josep Homedes: writing – review and editing, funding acquisition. Marta Salichs: conceptualization, methodology, project administration, writing – original draft. Shea Beasley: writing – review and editing. Antonio Arcas: writing – review and editing, formal analysis. Isaac Carrasco: writing – original draft, methodology.
Funding
This work was supported by Ecuphar Veterinaria SLU (Animalcare Group).
Conflicts of Interest
Isaac Carrasco has received unrelated payment from Zoetis, Leti‐Pharma, MSD Animal‐Health, Dechra, Vetnova, Elanco, Bioiberica, Boehringer‐ingelheim, Ceva, Hill's, Vetoquinol, Virbac and Ecuphar for lecturing and/or consulting. Marta Salichs and Josep Homedes are full employees of Ecuphar Veterinaria SLU (Animalcare Group). Shea Beasley is a consultant for Animalcare Group. Antonio Arcas has no conflicts of interest.
Supporting information
Figure S1: Quality‐of‐life (QoL) of the animals at the end of the study (D28) in the animals treated with the probiotic‐based ear drops (PED) only and in the animals treated with the PED and concomitant medications (PED+) and on D14 in the animals treated with the PED only.
Table S1: Clinical assessment and scores used in the study as indicated in the 0–3 Otitis Index Score (OTIS3) scale.
Acknowledgements
We graciously thank many veterinary surgeons (Alejandro Ojeda, Annabel Dalmau, Baltasar Fernandez, David Sanmiguel, Eliseo Zuriaga, Luis Bernal, Marcos Fernández, Marta Martínez and Maria José Guerrero from Spain; Chiara Caporali, Ilaria Cattin, Chiara Ferrucci, Luca Luciani, Fabiano Necci, Gloria Noris, Francesca Pezzato and Roberta Sartori from Italy) for their profound work in recruitment, assessments and data capture, as well as Cristina Mateu and Sara Barezzi for their work recruiting all of the participating veterinary surgeons and monitoring the conduct of the study. We also thank Eliseo Zuriaga and Luis Bernal for providing the photographs included in this paper.
Data Availability Statement
The data that support the findings of this study are available from the corresponding author upon reasonable request.
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Associated Data
This section collects any data citations, data availability statements, or supplementary materials included in this article.
Supplementary Materials
Figure S1: Quality‐of‐life (QoL) of the animals at the end of the study (D28) in the animals treated with the probiotic‐based ear drops (PED) only and in the animals treated with the PED and concomitant medications (PED+) and on D14 in the animals treated with the PED only.
Table S1: Clinical assessment and scores used in the study as indicated in the 0–3 Otitis Index Score (OTIS3) scale.
Data Availability Statement
The data that support the findings of this study are available from the corresponding author upon reasonable request.