Probiotic Engraftment and Suppression of Canine Otitis Externa Pathogens by Probiotic Ear Drops

ABSTRACT

Background

Lactobacillaceae have shown promise with their potential to outcompete pathogens and restore a healthy microbial balance in otitis externa (OE).

Hypothesis/Objectives

This study aimed to evaluate the presence of viable Lactobacillaceae over time and in vitro ability to inhibit growth of common OE pathogens.

Animals

Fifteen healthy dogs were enrolled and randomised into five groups (n = 3 per group) to receive six probiotic ear drops containing live Lactiplantibacillus plantarum YUN‐V2.0 and Lacticaseibacillus rhamnosus YUN‐S1.0.

Materials and Methods

Ear swabs were taken 24, 48, 72, 96 h and 7 days post single application for culturing. For pathogen inhibition, clinical isolates of Pseudomonas aeruginosa , Staphylococcus pseudintermedius and Malassezia pachydermatis were tested against the probiotic ear drop and antimicrobial disks of florfenicol 30 μg, gentamicin 30 μg, marbofloxacin 5 μg, miconazole 10 μg, neomycin 120 μg and terbinafine 1.5 μg.

Results

A relatively basal low abundance of commensal and Lactobacillaceae micro‐organisms was detected (1.34 × 10³ colony‐forming units [cfu]/mL). At 24 h post‐application, Lactobacillaceae increased significantly (2.3 × 10⁶ cfu/mL; p < 0.001), and remained above 10⁵ cfu/mL at 1 week post‐application (1.6 × 10⁵ cfu/mL). Lactobacilli demonstrated better growth inhibition of P. aeruginosa than gentamicin and marbofloxacin, and of S. pseudintermedius than gentamicin, neomycin and marbofloxacin. For M. pachydermatis similar growth inhibition versus miconazole and terbinafine was observed.

Conclusions and Clinical Relevance

These results suggest that probiotic strains exhibit excellent retention and can inhibit the growth of S. pseudintermedius, P. aeruginosa , and M. pachydermatis.

Background: Lactobacillaceae have shown promise with their potential to outcompete pathogens and restore a healthy microbial balance in otitis externa (OE).

Hypothesis/Objectives: This study aimed to evaluate the presence of viable Lactobacillaceae over time and in vitro ability to inhibit the growth of common OE pathogens.

Conclusions and Clinical Relevance: These results suggest that probiotic strains exhibit excellent retention and can inhibit the growth of Staphylococcus pseudintermedius , Pseudomonas aeruginosa , and Malassezia pachydermatis.

1. Introduction

The microbiological causes of canine ear conditions have been well‐documented, with Staphylococcus pseudintermedius and Malassezia pachydermatis being the most frequently isolated pathogens in clinical cases [1]. By contrast, the ear microbiota of clinically healthy dogs is described as diverse and compositionally balanced, with a naturally high abundance of commensal taxa such as Lactobacillaceae [2]. These bacteria are considered safe for animals, humans and the environment (EFSA), and may play a role in maintaining otic homeostasis.

Recent microbiome surveys have highlighted the complexity of the canine ear ecosystem, showing that microbial diversity is a hallmark of health, while reduced diversity and dominance of opportunistic taxa are associated with dysbiosis [2]. In this survey of pathogens implicated in canine ear infections, 78.3% of the clinically affected ear samples had microbial overgrowth, with 69.8% showing bacterial overgrowth, 16.3% fungal overgrowth, and 7.0% with both bacterial and fungal overgrowth [2]. Alterations of the skin's bacterial community composition are associated with OE in dogs, over‐representing Staphylococcus spp., Pseudomonas spp., and Proteus spp. [1, 3, 4, 5] Otitis externa (OE) is a common complaint in canine veterinary practice and can be observed following predisposing, primary, secondary or perpetuating factors (PSPP) [6]. Allergic dermatitis, known to be associated with microbial dysbiosis, is the most common aetiology of OE, accounting for ≤ 75% of the underlying primary causes [7, 8]. The main pathogens reported in the literature are various bacteria, of which S. pseudintermedius represents > 70% when cultured on growth media, followed by M. pachydermatis in 30%–60% of OE patients, depending on study population [1, 8]. Biofilm formation by M. pachydermatis, S. pseudintermedius , and Pseudomonas aeruginosa in dogs has been reported to influence their virulence, as well as contributing to reduced treatment efficacy [9, 10, 11].

With the advancement of next‐generation DNA sequencing (NGS) technologies, recent studies have provided a more detailed view of microbial changes associated with OE. Interestingly, even in OE‐affected dogs that were not experiencing active clinical signs, the microbiota remained distinct from that of healthy dogs, showing reduced alpha diversity and a persistent shift in bacterial composition, particularly with an increased presence of Staphylococcus spp. and Firmicutes [4]. These findings suggest that alterations in the microbiota may persist beyond the symptomatic phase of OE, potentially contributing to the high recurrence rate observed in affected dogs.

Moreover, OE is frequently associated with the overuse of antibiotics, which can contribute to antimicrobial resistance [12]. Therefore, there is an increasing need to explore alternative treatments that can help maintain a balanced ear microbiome. Probiotics, particularly Lactobacillaceae, have shown promise in this regard, with their potential to outcompete harmful pathogens and restore a healthy microbial balance [13]. Studies on the microbiome of the external ear canal in healthy dogs showed that Lactobacillaceae were among the most common genera [14]. L(+) lactic acid has been used commonly in ear drops yet has been currently placed under REACH regulation, and therefore replaced with alternatives such as boric acid and tris‐EDTA [15]. For a topical otic formulation with pathogenic preventive and microbiome balancing capacity, live Lactobacillaceae strains have shown to reduce pathogens, and have the potential to confer resistance to otitis in children [16]. Lactobacillaceae are natural habitants of the skin, providing a range of small molecule compounds to ensure their habitat space [17]. Live Lactobacillaceae adhere to skin and mucus, [13] and epithelial adhesion prolongs the presence of the probiotic on the skin enabling bacteria metabolites to interact with host cells and commensal bacteria on the skin [18, 19, 20]. Lactobacillaceae have immunomodulatory capacity associated with a reduction in excessive skin inflammation, [19] which is mediated by bacterial metabolites and cell wall‐associated or excreted microbe‐associated molecular patterns (MAMPs) [13, 21]. Lactobacillaceae also enhance the skin barrier function, which is often disrupted as a result of infection or inflammation associated with skin diseases [13]. proAuris (Ecuphar/Animalcare Group) is a topical hygiene probiotic ear drops product for outer ear application containing approximately 10⁹ cfu/mL of Lactiplantibacillus plantarum YUN‐V2.0 and Lacticaseibacillus rhamnosus YUN‐S1.0 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 sensitive ears and microbiome rebalance following antimicrobial treatment.

This study aimed to demonstrate the engraftment and persistence of two Lactobacillaceae strains on the skin of the outer ear following a single application, and furthermore, to evaluate the antagonistic potential of a probiotic product containing these strains in reducing typical pathobionts/pathogens associated with OE in dogs, in comparison to conventional antimicrobials.

2. Materials and Methods

2.1. Ethics

The in vivo engraftment study was conducted under good clinical practice and as per local legislation on the use of animals for clinical studies. A written informed consent was signed by the owner of the animals before the start of the study.

2.2. Engraftment Study

This test was performed to assess the Lactobacillaceae viability and engraftment in the ear of healthy dogs after a single application of the probiotic ear drops.

2.3. Study Population

Fifteen healthy dogs of any breed, weight and sex were enrolled from a dog shelter (Het Zilveren mandje, Lokeren, Belgium) based on the absence of a history of ear disease or skin problems. Dogs had to be older than 6 months and not presenting any sign compatible with OE or showing any ear discharge at the time of inclusion. Dogs should not have received any antibiotics and/or antimycotics either systemic or topical within 30 days before enrolment. Also, the use of ear cleaners was forbidden within 7 days before the start of the study. Concomitant medications were forbidden through the in‐life phase of the study.

Dogs were randomly allocated into five groups (n = 3 per group), each corresponding to a different sampling time point post‐application (pa): 24, 48, 72, 96 and 168 hpa. This design allowed assessment of probiotic viability over time in the external ear canal. See Table 1. On Day (D) 0, all dogs received one application of six drops of the probiotic product in both external ear canals. Swabs were collected from both canals under a pre‐established ear sampling schedule. Samples were taken by a single veterinary surgeon to reduce sampling bias. The safety of the product was monitored during the study by clinical observations of the personnel in charge of the care of the animals and documentation of adverse events (AEs).

TABLE 1.

Ear swab sample collection scheme for Lactobacillaceae and commensal bacteria in healthy dogs.

Day (D)	Sampling time (hpa) b	Group 1 (n = 3)	Group 2 (n = 3)	Group 3 (n = 3)	Group 4 (n = 3)	Group 5 (n = 3)
D0 a	0 c	X	X	X	X	X
D1	24	X
D2	48		X
D3	72			X
D4	96				X
D7	168					X

^a Product application.

^b Number of hours post‐application (hpa) of product into the outer ear.

^c Sampling performed before product application. This was recorded as baseline.

2.4. Sample Collection and Processing

The ear swabs (ESwab; Copan) were taken as follows: The skin of the external ear canal was gently rubbed with a swab for 10 s and immediately secured in the collection and transport system tube (Copan Liquid Amies Elution Swab 2 mL) and stored at 4°C. Within 48 h of sampling, swabs were shipped on dry ice to YUN NV, Belgium for microbiological analysis. For resuscitation buffer, physiological saline (0.85%) was used. Swabs were then transferred from the collection tubes to 15 mL falcon tubes with resuscitation buffer and vortexed for 15 s with a Mini Vortex Mixer (Labbox) with a fixed speed of 3000 rpm. A 10‐fold serial dilution series was prepared in physiological saline (0.85%). From appropriate dilutions of 10⁻¹—10⁻⁴, 100 μL were spotted on Man Rogosa Sharpe (MRS; Biokar) agar (20 mL layer on a standard 9 cm petri dish) for evaluation of Lactobacillaceae viability and on CASO (Biokar) agar for evaluation of commensal ear microbiota. MRS and CASO plates were incubated for 48–72 h at 35°C to allow colony visualisation. All plates were counted once colonies were clearly visible and within the countable range of 20–200 colonies.

2.5. Pathogen Inhibition Study

A single clinical isolate of P. aeruginosa , S. pseudintermedius , and M. pachydermatis from dog ears presented with OE identified using matrix‐assisted laser desorption/ionisation time‐of‐flight (MALDI‐TOF) mass spectrometry (MS) at the Faculty of Veterinary Medicine, University of Gent, Belgium, were tested for antimicrobial susceptibility. proAuris containing L. plantarum YUN‐V2.0 and L. rhamnosus YUN‐S1.0 and antimicrobial disks of florfenicol 30–240 μg, gentamicin 30 μg, marbofloxacin 5 μg, miconazole 10 μg, neomycin 120 μg, and terbinafine 1.5 μg were tested against the micro‐organisms as described in Table 2. Viable Micrococcus luteus broth culture or sterile physiological saline water served as negative controls.

TABLE 2.

Exclusion capacity of the probiotic ear drops (ProAuris) towards ear pathogens isolated from dog ears with otitis externa (OE) evaluated against antimicrobials commonly isolated from ears with OE, with Micrococcus luteus as a negative control.

Pathogen strain	Second layer agar	Antimicrobial disk
Pseudomonas aeruginosa	CASO agar	Florfenicol 240 μg
		Gentamicin 30 μg
		Marbofloxacin 5 μg
Staphylococcus pseudintermedius	CASO agar	Florfenicol 30 μg
		Gentamicin 30 μg
		Neomycin 120 μg
		Marbofloxacin 5 μg
Malassezia pachydermatis	Sabouraud agar	Terbinafine 1.5 μg
		Miconazole 10 μg

The method was adapted from the protocol described by van den Broek et al. [22] with the following procedure: 10 μL of proAuris ear drop suspension were spotted on MRS agar (Difco) to create a spot of approximately 6 mm, and 10 μL of a M. luteus broth culture were spotted on the same MRS agar plate. Plates were incubated at 35°C for 48 h to allow the Lactobacillaceae to grow. Then the plates were UV‐treated to inactivate Lactobacillaceae to prevent overgrowth in the overlay agar and to obtain release of antimicrobial compounds [22]. An overlay of CASO agar or Sabouraud agar depending on the pathogen was poured over the plate and covered with a pathogen suspension. The pathogen suspension was prepared by swabbing the solidified overlay agar with a saline suspension made from a colony picked from a preculture plate. An antibiotic disk was placed on the dry agar surface for positive control. Plates were incubated under aerobic conditions at 35°C for 24 h and inhibition zones were measured (in mm) on the agar plates. To ensure reproducibility and account for biological variability, each strain was assessed in three independent biological replicates, each plated and processed separately.

In order to assure the quality of the product (proAuris), viability of the Lactobacillaceae was followed over time. The microbiological quality of the product was analysed by performing total aerobic microbial count (TAMC, non‐lactobacilli), total yeast and mould count (TYMC) plating and checking for exclusion of pathogens Staphylococcus aureus, P. aeruginosa and Candida albicans .

2.6. Statistical Analysis

All statistical analyses were performed using sigma plot (v16 2024; Grafity). Differences in Lactobacillaceae counts before and after probiotic application were assessed using a one‐way ANOVA performed on log‐transformed data to meet normality and variance assumptions. Post hoc multiple comparisons were carried out using the Holm–Sidak method, comparing each time point to baseline values (before probiotic application). Data are presented as average cfu/mL ± standard deviation (SD). For the pathogen inhibition, a Welch's two‐tailed t‐test was used and data are presented as inhibition zone (mm) ± SD. A p‐value of < 0.05 was considered statistically significant.

3. Results

3.1. Engraftment Study

Before application of the probiotic product on D0, a relatively low abundance of commensal cultivable micro‐organisms was detected in the external ear canal of 15 healthy dogs with calculated average of 1.34 × 10³ cfu/mL on CASO (commensal bacteria) and 960 cfu/mL on MRS (lactic acid bacteria). At 24 hpa of the probiotic ear drops to the external ear canal of both ears, an increase of Lactobacillaceae was observed (2.3 × 10⁶ cfu/mL) that remained stable above 10⁶ cfu/mL up to 3 days (72 hpa) after application. Lactobacillaceae gradually decreased to 6.4 × 10⁵ cfu/mL in 4 days (96 hpa) and to 1.6 × 10⁵ cfu/mL after 1 week. Lactobacillaceae counts were significantly higher versus baseline at all time points (p < 0.001) (Figure 1). It is important to note that cfu/mL values provide an estimate of bacterial abundance yet do not directly correspond to absolute bacterial counts, as they are based on swabs transferred into 1 mL of fluid, vortexed, and subsequently diluted for plating which increased variability. After probiotic application the abundance of the commensal microbiota remained at levels around 10²–10³ cfu/mL throughout the study. All cfu counts for the Lactobacillaceae, and the commensal ear microbiome are included as Table S1 in the Supporting Information S1. No adverse events were observed in any of the treated dogs throughout the study.

FIGURE 1.

Average counts of cultivable Lactobacillaceae recovered from swabs taken from the external ear canal. After taking the baseline sample on Day 0 (T0h), a single dose of the probiotic ear drops containing approximately 10⁹ cfu/mL Lactobacillaceae was applied in the canine external ear canal. The baseline T0h value corresponds to the average of all dogs included in the study (n = 15). The subsequent time point values correspond to the group average (n = 3) as described in the sample collection scheme. Statistical significance versus baseline (T0h) was assessed on log‐transformed cfu/mL. *p < 0.001, considered statistically significant compared to T0h.

3.2. Pathogen Inhibition Study

The ear drops, containing the live lactobacilli, demonstrated significantly higher inhibition of P. aeruginosa compared to gentamicin (p = 0.0223) and marbofloxacin (p = 0.0147), while P. aeruginosa was resistant to florfenicol at all concentrations tested. For S. pseudintermedius , inhibition by the probiotic ear drops was significantly greater than neomycin (p = 0.0195) and marbofloxacin (p = 0.0017), and comparable to gentamicin (p = 0.1813) and florfenicol (p = 0.5168). Against M. pachydermatis, the probiotic ear drops showed inhibition similar to terbinafine (p = 0.7372) and slightly higher than miconazole (p = 0.0654), although these differences were not statistically significant. The exact values for the inhibition zones (in mm ± SD) for all tested antimicrobials and for the probiotic ear drops are included in Table 3 and depicted in Figure 2.

TABLE 3.

Average inhibition zones (in mm ± standard deviation [SD]) for Lactobacillaceae included in the probiotic ear drops (proAuris 10 μL), neomycin, gentamicin, florfenicol and marbofloxacin against Staphylococcus pseudintermedius ; for Lactobacillaceae, gentamicin, florfenicol and marbofloxacin against Pseudomonas aeruginosa , and miconazole and terbinafine against Malassezia pachydermatis.

Antimicrobial/Probiotic ear drop	Staphylococcus pseudintermedius	Pseudomonas aeruginosa	Malassezia pachydermatis
Neomycin 120 μg Probiotic ear drop 10 μL	21.3 ± 1.7 33.5 ± 3.9*	ND	ND
Gentamicin 30 μg Probiotic ear drop 10 μL	26.6 ± 1.6 29.1 ± 2.1	13.1 ± 2.1 31.6 ± 5.9*	ND
Florfenicol 30 μg Probiotic ear drop 10 μL	30.6 ± 1.1 29.9 ± 1.3	Resistant a 48.03	ND
Marbofloxacin 5 μg Probiotic ear drop 10 μL	27.3 ± 0.9 32.6 ± 0.7*	19.2 ± 2.1 48.3 ± 7.3*	ND
Miconazole 10 μg Probiotic ear drop 10 μL	ND	ND	24.2 ± 0.5 28.9 ± 2.3
Terbinafine 1.5 μg Probiotic ear drop 10 μL	ND	ND	30.2 ± 2.5 29.3 ± 3.5

Abbreviation: ND, not determined.

^a Resistant to florfenicol up to tested 240 μg.

^* p < 0.05.

FIGURE 2.

In vitro inhibition of canine ear pathogens by probiotic ear drops (PRO), antibiotics/antimycotic (AB/AM) and a negative control ( Micrococcus luteus—ML). Each panel (a–f) shows inhibition zones for a single pathogen: Staphylococcus pseudintermedius (a, d), Pseudomonas aeruginosa (b, e), and Malassezia pachydermatis (c, f). Antimicrobials used were gentamicin (a, b), neomycin (d), marbofloxacin (e), terbinafine (c), and miconazole (f). For exact inhibition zones in mm, see Table 3.

4. Discussion

In this study, the two probiotic strains included in proAuris probiotic ear drops ( L. plantarum YUN‐V2.0 and L. rhamnosus YUN‐S1.0) have shown an intrinsic capacity to inhibit the growth of the canine ear‐derived pathogens tested, including S. pseudintermedius , P. aeruginosa and M. pachydermatis, with similar in vitro activity to the antimicrobials used in this study as positive controls. The comparison with antibiotics in this study serves as a reference for in vitro efficacy, yet direct clinical equivalence should not be inferred from these results alone. This pathogen inhibition is likely to be attributed to their multifactorial mode‐of‐action (MoA) which includes competition for nutrition, the production of antimicrobial peptides, lactic acid and other bioactive molecules, and a shift in the pH of the environment, as reported previously for probiotic lactobacilli [13]. It should be emphasised that antipathogenic properties are not inherent to all Lactobacillaceae; these effects are typically strain‐dependent. This highlights the importance of selecting well‐characterised probiotic strains for targeted applications. Furthermore, the presence of caprylic/capric triglycerides in the formulation does not seem to interfere with the growth of the probiotic Lactobacillaceae nor the pathogens. In this study, the clinical isolate of P. aeruginosa was found to be resistant to florfenicol at different concentrations up to 240 μg, which is not entirely surprising, as it is known that most strains of P. aeruginosa exhibit resistance to florfenicol [23]. This finding underscores the importance of accurate microbial identification in cases of otitis, as empirical use of ear medications containing florfenicol may be ineffective and potentially contribute to resistance when rod‐shaped bacteria such as P. aeruginosa are involved.

In dogs with OE, microbial alpha‐diversity is lower compared to healthy animals, allowing opportunistic pathogens such as Staphylococcus and Pseudomonas to dominate, with reported increases in abundance of ≤ 65% [4, 5, 24]. Additionally, occurrence of yeast in the external ear canal of dogs with OE varies between 30% and 60% depending on the studied population [1, 24]. Given these shifts and knowing that the tested probiotic strains exhibit inhibitory activity against these pathogens, our findings support the hypothesis that probiotic lactobacilli may help restore a more balanced ear microbiome. Long‐term, this effect may contribute to stabilising microbial communities in a way that reduces pathogen overgrowth, as suggested by Leonard et al. [14]. While these findings are promising, the observed inhibitory effects were only demonstrated in vitro; statistical analyses were performed to support the observed effects. However, the primary aim was to characterise the in vitro potential of these strains, which were specifically selected for their intrinsic activity. Therefore, in vivo studies with a larger number of diseased animals and longer duration would be needed to confirm these assumptions. Together with efficacy, the probiotic ear drops also offer a safe alternative to antibiotics, antimycotics and biocides which reduce not only harmful pathogens, but also beneficial organisms and potentially lead to antimicrobial resistance [25]. This concern is underscored by reports of Staphylococcus spp., Pseudomonas spp. and M. pachydermatis exhibiting resistance to most of the commonly used antimicrobials [24]. The use of probiotic Lactobacillaceae may offer a complementary strategy by supporting microbial balance and potentially mitigating the selective pressures that drive antimicrobial resistance [26].

The abundance of Lactobacillaceae remained relatively stable in the external ear canal of healthy dogs after application of the probiotic ear drops. After a single dose of the probiotic ear drops, viable Lactobacillaceae were recovered at levels above the suggested probiotic threshold of 10⁵ cfu/mL after 1 week, suggesting sustained probiotic activity for several days. Additionally, the number of commensal skin microbes in healthy dogs appeared relatively low, approximately 10²–10³ cfu/mL at baseline, and remained within this range following the application of the topical probiotic product. Given the low microbial counts, the minor fluctuations observed are consistent with normal biological variation and were not statistically significant. As a limitation of the study, the commensal micro‐organisms were identified using MRS and CASO media, hindering detection of the exact proportion of Lactobacillaceae within the commensal ear community owing to the restrictions of cultivation‐based methods. Another limitation could be the sampling of different groups of animals at each time point rather than on the same animals, which limits temporal comparisons and precludes inference of within‐subject changes over time. However, the goal of the study was to evaluate how long probiotic Lactobacillaceae would remain detectable in the ear canal after a single application, rather than to follow individual dogs longitudinally. Additionally, for the antipathogenic inhibition assays, only one clinical isolate per organism was tested, which may not fully capture the diversity of pathogen responses encountered in clinical settings. However, given the multifactorial MoA of probiotics, including competition for nutrition and space, and the production of lactic acid and antimicrobial peptides in situ, the likelihood of resistance among other clinical isolates is expected to be lower than typically observed with antibiotics.

These findings demonstrate promising probiotic engraftment and antipathogenic activity, yet further studies could provide deeper insights into the long‐term dynamics of the ear microbiome following repeated applications. Understanding the effects of an optimal dosing regimen on the microbial community would further clarify its role in maintaining a balanced ear microbiome. Building on these findings, the demonstrated retention of Lactobacillaceae for up to 1 week suggests that daily application may not be necessary. Instead, a dosing regimen of every other day could be sufficient to rebalance the ear microbiota within the external ear canal. Additionally, the antipathogenic activity of the probiotic strains highlights their potential in the management of microbial dysbiosis towards a healthy ear microbiome with sufficient abundance of Lactobacillaceae [14]. In conclusion, L. plantarum YUN‐V2.0 and L. rhamnosus YUN‐S1.0 in proAuris probiotic ear drops exhibit excellent retention in the healthy canine external ear canal. Furthermore, the probiotic ear drops effectively inhibited the growth of otic pathogens S. pseudintermedius, P. aeruginosa and M. pachydermatis in vitro. These results encourage the continued exploration of probiotic‐based therapies as a novel and microbiome‐friendly strategy for the prevention and management of canine OE.

Author Contributions

Hanne Gagroo: conceptualization, investigation, writing – review and editing. Shea Beasley: conceptualization, writing – original draft, methodology, supervision. Alix Simons: conceptualization, investigation, writing – review and editing. Tim Henkens: conceptualization, methodology, writing – review and editing. Ingmar Claes: conceptualization, methodology, supervision, writing – review and editing. Josep Homedes: writing – review and editing, funding acquisition. Marta Salichs: conceptualization, methodology, project administration, writing – original draft.

Funding

Ecuphar Veterinaria SLU (Animalcare Group).

Conflicts of Interest

Marta Salichs and Josep Homedes are full employees of Ecuphar Veterinaria SLU (Animalcare Group). Shea Beasley is a consultant for Animalcare Group. Hanne Gagroo, Alix Simons, Tim Henkens, and Ingmar Claes are full employees of YUN NV.

Supporting information

Table S1: colony‐formin unit counts for Lactobacillaceae (MRS) and commensal ear microbiome (CASO).

Data Availability Statement

The data that support the findings of this study are available from the corresponding author upon reasonable request.