Therapeutic and Formulation Innovations in the Management of Canine Otitis Externa

The antimicrobial activity of cinnamon essential oil and cinnamaldehyde against bacterial and fungal pathogens associated with canine otitis externa, as well as the effect of their combination with EDTA were investigated. Antimicrobial susceptibility testing was performed using the broth microdilution method while spot-plating technique was used to determine their bactericidal activity. Time-kill kinetics and checkerboard assays were performed to confirm the bactericidal activity and combination effects of the compounds. Cinnamon oil and cinnamaldehyde exhibited antimicrobial activity against Gram-positive and Gram-negative pathogens, as well as Malassezia pachydermatis. Synergistic interaction was shown when EDTA (672μgml-1 ) was combined with cinnamon oil (41μgml-1 ) and cinnamaldehyde (22μgml-1 ) against Pseudomonas aeruginosa. Cinnamaldehyde exhibited significantly stronger antimicrobial activity than cinnamon bark oil. Cinnamon essential oil and cinnamaldehyde, either used alone or in combination with EDTA, were effective against the causative micro-organisms of canine otitis externa. The data suggest that cinnamaldehyde could be a promising antimicrobial agent against canine otitis externa. This study shows that cinnamon essential oil and cinnamaldehyde, especially the latter, could be used in combination with EDTA as novel treatment for sensitive and resistant bacterial and fungal pathogens involved in canine otitis externa.

In canine otitis externa (OE), biofilm-producing bacteria are frequently present but biofilm may be underdiagnosed clinically. The study aimed to investigate an association between clinical and cytological findings with bacteriological data from dogs with OE, to establish, through Environmental Scanning Electron Microscope (ESEM) examination, whether the presence of biofilm in vivo can be predicted and to evaluate the impact of biofilm on antimicrobial susceptibility tests. Fifty-six dogs showing clinical signs of OE were enrolled. One cotton swab each was collected for ESEM, bacterial culture and susceptibility testing and for cytology. Staphylococcus pseudintermedius (n = 42, 48.8%) and Pseudomonas aeruginosa (n = 26, 30.2%) were tested for their ability to form biofilm. Minimum Inhibitory Concentrations (MIC), Minimal Biofilm Inhibitory Concentrations (MBIC) and Minimal Biofilm Eradication Concentrations (MBEC) towards enrofloxacin, gentamicin, polymyxin B and rifampicin were determined. Pseudomonas aeruginosa was positively associated with the biofilm clinical evaluation (p < 0.01) and neutrophils (p < 0.05), nuclear streaks (p < 0.01) and rods bacteria (p < 0.01) on cytology. S. pseudintermedius was associated with a low presence of neutrophils. There was a statistical correlation between clinical and cytological biofilm presence (p ≤ 0.01), but none with the biofilm production assay nor ESEM biofilm detection. No differences were found comparing the results of MIC and MBIC. MBEC results showed higher values than MIC and MBIC for all antimicrobials tested (p ≤ 0.001). Biofilm presence in OE was often underdiagnosed. Even if there is no specific clinical or cytological pattern related to biofilm, its presence should always be suspected.

Otitis externa is a common presenting complaint in practice. Ear infections by Pseudomonas aeruginosa are particularly problematic due to the organism's high level of resistance and ability to damage the tympanum. Treatment should be based on susceptibility testing although minimum inhibitory concentrations (MICs) are not available for all treatment options. Silver sulfadiazine has been used in cases of recurrent P.aeruginosa otitis, although a MIC for silver sulfadiazine as a single agent has not been established. To describe susceptibility patterns of P.aeruginosa isolated from canine otitis externa and determine the MIC for silver sulfadiazine and other topical antimicrobials. Thirty-six P.aeruginosa isolates were collected from client-owned dogs, suffering from otitis externa. Susceptibility patterns were established using disc diffusion susceptibility testing against 17 antimicrobial agents. For determination of the MIC, selected strains were tested against increasing concentrations of marbofloxacin, enrofloxacin, gentamicin, polymyxin B and silver sulfadiazine using broth microdilution. For nine of 17 antimicrobial agents, complete resistance was seen in all isolates tested via disk diffusion susceptibility testing. Approximately 94% and 96% of isolates were susceptible to gentamicin and imipenem, respectively. These findings were consistent with broth dilution, where all strains were susceptible to gentamicin. Resistance was higher against polymyxin B and the fluoroquinolones. Silver sulfadiazine was effective invitro with a MIC ranging from 1 to 64μg/mL. As the MIC of silver sulfadiazine was lower than the concentration in a 1% preparation, such a product potentially represents a treatment option for dogs with P.aeruginosa otitis.

The emergence and global spread of antimicrobial resistance among bacterial pathogens demand alternative strategies to treat life-threatening infections. Combination drugs and repurposing of old compounds with known safety profiles that are not currently used in human medicine can address the problem of multidrug-resistant infections and promote antimicrobial stewardship in veterinary medicine. In this study, the antimicrobial activity of robenidine alone or in combination with ethylenediaminetetraacetic acid (EDTA) or polymyxin B nonapeptide (PMBN) against Gram-negative bacterial pathogens, including those associated with canine otitis externa and human skin and soft tissue infection, was evaluated in vitro using microdilution susceptibility testing and the checkerboard method. Fractional inhibitory concentration indices (FICIs) and dose reduction indices (DRI) of the combinations against tested isolates were determined. Robenidine alone was bactericidal against Acinetobacter baumannii [minimum inhibitory concentrations (MIC) mode = 8 μg/ml] and Acinetobacter calcoaceticus (MIC mode = 2 μg/ml). Against Acinetobacter spp., an additivity/indifference of the combination of robenidine/EDTA (0.53 > FICIs > 1.06) and a synergistic effect of the combination of robenidine/PMBN (0.5 < FICI) were obtained. DRIs of robenidine were significantly increased in the presence of both EDTA and PMBN from 2- to 2048-fold. Robenidine exhibited antimicrobial activity against Escherichia coli, Klebsiella pneumoniae, and Pseudomonas aeruginosa, in the presence of sub-inhibitory concentrations of either EDTA or PMBN. Robenidine also demonstrated potent antibacterial activity against multidrug-resistant Gram-positive pathogens and all Gram-negative pathogens isolated from cases of canine otitis externa in the presence of EDTA. Robenidine did not demonstrate antibiofilm activity against Gram-positive and Gram-negative bacteria. EDTA facilitated biofilm biomass degradation for both Gram-positives and Gram-negatives. The addition of robenidine to EDTA was not associated with any change in the effect on biofilm biomass degradation. The combination of robenidine with EDTA or PMBN has potential for further exploration and pharmaceutical development, such as incorporation into topical and otic formulations for animal and human use.

BackgroundOtitis externa is a common problem in small animal practice. Compliance with daily treatment is a major cause of treatment failure. The hypothesis tested is that a novel otic gel applied to the ear canal twice with a one-week interval is as efficacious as a daily otic suspension in the treatment of canine otitis externa. The study included 286 privately owned dogs with otitis externa.In this single blinded randomized study, enrolled dogs received either an otic gel containing 1% florfenicol, 1% terbinafine and 0.1% betamethasone acetate twice with a one-week interval or a suspension containing hydrocortisone aceponate, miconazole and gentamicin daily for 5 days. Ears were cleaned with saline prior to administration of the first dose of medication. Dogs were evaluated at day (D) 0, 7, 28 and 56 with an otitis index score (OTIS-3), otic culture and cytology, pain and pruritus, and overall response to treatment (owner and investigator evaluation). Outcome measures were improvement of the OTIS-3 and number of dogs in clinical remission at each time point.ResultsOTIS-3 decreased significantly (p < 0.0001) by 63 and 64% for the otic gel and by 63 and 61% for the suspension on D28 and D56 respectively. There was no significant difference between groups at any time point with regard to clinical success, pain, pruritus, overall assessments or otic cytology and culture. The treatment response was considered excellent or good by approximately three quarters of both the clinicians and Owners. Otitis recurrence at D56 was seen in 11% of both groups. Adverse events attributable to the ear medications were not noted.ConclusionsAdministering an otic gel twice at a one-week interval is an effective, safe and convenient way to treat canine otitis externa.

Therapeutic interventions (TI) can be drugs, devices, or complex interventions. Category independent, a TI must produce a clinical benefit that the patient perceives as RELEVANT for his or her well-being. This benefit must compensate the risks and the overall burden the intervention represents for the individual, the family and the society. We are looking for drugs in HD that can produce a sufficiently large effect (or can contribute to such an effect in combination with other TI) in one or more of the affected domains of HD (motor, behaviour, cognition, metabolism) with an acceptable safety profile. The beneficial effect can be either the deferral of the disease manifestation or the reduction of symptom intensity; or both. HD is a neurodegenerative disorder not simpler than Alzheimer9s or Parkinson9s disease, sharing progressive selective neuronal death, long-term compensatory mechanisms and numbers of accessory pathogenic processes, which might be useful as auxiliary therapeutic targets. The underlying pathogenic processes are evidently similar, demonstrated by the current efforts of the scientific community revising the concepts of the evolution in these diseases. Regarding the commonalities, it is considered that there is a preclinical period without detectable clinical or biomarker changes, a presymptomatic period where only biomarkers indicate changes, a premanifest period with robust biomarker and first clinical changes and finally the manifest period with manifestation of classical symptoms of the disease. Drugs that will be used in these different periods will have very different characteristics. It is contentious whether or not a drug should be considered in the early periods of slow progressing diseases like HD if its safety profile is riskier than for example, aspirin as prophylaxis for myocardial infarction. This situation will be different for juvenile HD. There is plenty of room for different trade-offs between the benefits and the risks, depending on the risk acceptance of individuals and the society, compliance issues and time horizons. HD is a monogenetic, fully penetrant disease which gives HD a head start advantage over the other neurodegenerative diseases in the search for targeted drugs. By knowing the gene and its ultimate product, it was possible to design the first specific interventions using iRNA technologies, which will enter clinical trials soon (early 2013). However, they are extremely interesting but highly experimental interventions. For issues as important as pharmacokinetics, techniques of application, brain diffusion, and dosage details still must be worked out. This will bring the discussion to the ideal characteristics of a drug being fully brain penetrant, and what technical challenges are acceptable if a TI offers a realistic promise of efficacy. In summary, in our search for drugs for HD, we expect to develop TI which are effective and have a manageable safety profile. In addition, we hope (1) to learn which is a drug9s best target population and to establish appropriate subgroups; (2) to define the proper disease phase in which drugs can be used for optimal results; and (3) to find the ideal dosage, regime and drug combination (as in chemotherapy protocols).

The diversity of species of the genus Staphylococcus sp. and the antimicrobial resistance of isolates from 151 unmedicated dogs of both sexes with a clinical diagnosis of otitis were recorded. Ninety-one isolates of Staphylococcus spp. were identified by biochemical reactions and tested for susceptibility to 15 antimicrobials. Coagulase-positive species were most common; S. pseudintermedius (38.4%), S. schleiferi schleiferi (15.4%), S. aureus (14.3%), S. epidermidis (11%), S. simulans (11%), S. schleiferi coagulans (8.8%) and S. saprophyticus (1.1%). All the isolates showed resistance to at least one drug and 89% were multiresistant. Amoxicillin combined with clavulanic acid and oxacillin were the most effective, while resistance was widely observed for neomycin and erythromycin. The results highlight the recognition and the potential need for bacterial culture with species identification and antimicrobial susceptibility tests for appropriate antimicrobial therapy.

An update on microbiological causes of canine otitis externa in Campania Region, Italy

Multidrug-resistant pathogens present a major global challenge in antimicrobial therapy and frequently complicate otitis externa in dogs. In vitro efficacy of oregano oil, thyme oil and their main phenolic constituents against bacterial and fungal isolates associated with canine otitis externa were investigated. It was hypothesized that the main phenolic components would have greater antimicrobial activity compared to the relative essential oil. Antimicrobial susceptibility testing was performed using broth microdilution with spot-plating technique to determine minimum inhibitory and bactericidal/fungicidal concentrations (MICs, MBCs and MFCs). A time-kill kinetics assay was performed to confirm the bactericidal and fungicidal activity of the oils and their phenolic constituents. One hundred bacterial and fungal isolates, including meticillin-susceptible Staphylococcus pseudintermedius (n=10), meticillin-resistant S.pseudintermedius (n=10), β-haemolytic Streptococcus spp. (n=20), Pseudomonas aeruginosa (n=20; including 10 isolates resistant to one or two antimicrobials), Proteus mirabilis (n=20) and Malassezia pachydermatis (n=20) from dogs with otitis externa were used. Oregano oil, thyme oil, carvacrol and thymol exhibited antibacterial activity against all bacterial and fungal isolates tested. MIC90 values ranged from 0.015 to 0.03% (146-292μg/mL) for the Gram-positive bacteria and P.mirabilis. For P.aeruginosa and M.pachydermatis, MIC90 values ranged from 0.09 to 0.25% (800-2,292μg/mL). Oregano oil, thyme oil, carvacrol and thymol showed good in vitro bactericidal and fungicidal activity against 100 isolates from dogs with otitis externa, including some highly drug-resistant isolates. These essential oils and their main phenolic constituents have the potential to be further investigated in vivo for the treatment of canine otitis externa.

Editorial: The challenge of mapping diagnostic categories onto developmental pathophysiology: DSM‐6 anyone?

Canine otitis externa (OE) presents a significant challenge in veterinary medicine due to its complex, multifactorial nature and the growing issue of antimicrobial resistance (AMR) associated with conventional antibiotic use. The objective of this study was to compare the efficacy of a novel, antibiotic-free topical ear solution (Therapy A) containing antimicrobial peptides and encapsulated plant extracts (chamomile, calendula, rosemary, and hops) against a standard conventional treatment (Therapy B) composed of gentamicin, betamethasone valerate, and clotrimazole. A longitudinal, randomized study was conducted over four weeks with 40 domestic dogs diagnosed with OE. The dogs were divided into two groups, each receiving one of the therapies. Evaluations were performed weekly, assessing clinical signs using the Otitis Index Scoring System (OTIS-3) and a pruritus visual analog scale (pVAS), as well as ear canal pH and cytology. The results showed that Therapy A provided similar clinical efficacy in OTIS-3 and pVAS scores that were comparable to Therapy B. Cytological analysis also revealed a significant reduction in microbial presence for both groups. Notably, Therapy A was clinically effective in two of the three dogs presenting multi-drug resistant (MDR) bacterial infections. The novel formulation also demonstrated a favorable safety profile, with no adverse drug reactions reported, in contrast to one dog in the conventional treatment group that experienced an adverse reaction. These findings suggest that the plant-based formulation is a safe and effective alternative for managing canine OE, offering a promising solution to reduce the reliance on antibiotics and corticosteroids.

The purpose of this study was to evaluate interlaboratory variation in isolation and antibiotic susceptibility pattern of Pseudomonas spp. as reported to veterinarians for cases of canine chronic bacterial otitis externa. Twenty-six dogs with unilateral or bilateral bacterial otitis externa from multiple referral practices were included in this prospective study. Triplicate samples collected simultaneously from the same location in the external ear canal were randomly submitted to three laboratories for culture and susceptibility testing. Pseudomonas spp. were isolated from 18 of 34 (53%) ears. All three laboratories agreed on the presence of Pseudomonas spp. in 15 (83.3%) ears sampled. However, two laboratories agreed on two (11.1%) occasions, and on one occasion (5.5%) Pseudomonas spp. were identified in only one laboratory. Minimum inhibitory concentration (MIC) susceptibilities to 11 antibiotics were compared between laboratories B and C. Using laboratory-defined susceptibility of sensitive (S), intermediate (I) and resistant (R), none of the 16 Pseudomonas spp. with MIC data reported had identical patterns of antibiotic susceptibility. Agreement in susceptibility to individual antibiotics was observed in 13 of 16 (81%) occasions for amikacin and gentamicin, 10 of 16 (63%) occasions for ticarcillin, and nine of 16 (56%) for enrofloxacin. These results indicate that Pseudomonas spp. were identified by all three laboratories chosen for this study in 83% of the time. Moreover, antibiotic susceptibility patterns and MIC values reported to veterinarians may not agree between laboratories. Veterinarians should interpret bacterial culture and susceptibility results with multiple caveats including variability between laboratories.

Background: Canine pyoderma and otitis externa are prevalent bacterial skin infections in veterinary practice, frequently complicated by the emergence of multidrug-resistant (MDR) pathogens. Objectives: To investigate the frequency, antimicrobial resistance (AMR) profiles, and frequency of MDR bacterial isolates from dogs with pyoderma or otitis externa in Hong Kong. Methods: A retrospective study of bacterial isolates from 215 clinical samples collected from dogs presenting with pyoderma (n = 63) or otitis externa (n = 152) at veterinary clinics across Hong Kong between 2018 and 2022. Bacterial isolates were identified and subjected to antimicrobial susceptibility testing against 13 antimicrobial classes. Results: Staphylococcus spp., particularly S. pseudintermedius, were the most commonly isolated species, followed by Pseudomonas spp. and Proteus spp. High resistance rates were observed for orbifloxacin (61.3% in pyoderma; 76.7% in otitis externa), doxycycline (59.3%; 69.2%), clindamycin (62%; 68.9%), and enrofloxacin (50%; 55.5%). Most isolates were sensitive to ofloxacin, ticarcillin-clavulanate, tobramycin, ciprofloxacin, cefpodoxime, cefuroxime, and cefixime. MDR was detected in 67.5% of pyoderma and 66.8% of otitis externa isolates. Gram-negative bacteria exhibited significantly higher MDR rates than Gram-positive isolates. The multiple antibiotic resistance (MAR) index averaged 0.41 for pyoderma and 0.52 for otitis externa isolates. We found no significant associations between MDR and non-modifiable risk factors (i.e., age, sex, breed, and reproductive status). Conclusions: These findings highlight the critical need for prudent antimicrobial use and continuous surveillance of AMR trends in companion animals. A higher focus should be placed on topical antiseptic therapy, with oral antibiotics used only in exceptional cases and after susceptibility testing. From a One Health perspective, the potential transmission of MDR bacteria between companion animals and humans underscores the importance of a coordinated approach to antimicrobial stewardship across both veterinary and human medicine.

Canine Malassezia dermatitis (CMD) and otitis externa are generally treated by antifungal drugs. However, azole-resistant strains have been isolated from canine skin and ear canals worldwide. Phytochemicals isolated from essential oils are effective alternatives for inhibiting Malassezia pachydermatis. To evaluate the usefulness of phytochemicals against azole-resistant isolates, we performed in vitro susceptibility testing using the phytochemicals carvacrol, citral, and thymol. Eight antifungal-resistant isolates were obtained from 7 cases of dermatitis and 1 case of otitis externa during 2022 and 2023 from dogs in Tokyo and Kanagawa, Japan. Fungal susceptibility to carvacrol, citral, and thymol were assessed using the modified broth microdilution method. The minimum inhibitory concentrations (MICs) of the phytochemicals in all isolates were as follows: 0.03 to 0.125% for carvacrol; 0.03 to 0.125% for thymol; and 0.03% to 0.125% for citral. Based on these results, carvacrol, citral, and thymol appear to be effective against azole-resistant strains. The phytochemicals appear to be effective for treating antifungal-resistant cases of CMD and otitis externa.

Development of a diagnostic model based on glycolysis-related genes and immune infiltration in intervertebral disc degeneration