Microbiological study of external otitis in dogs from North Rhine-Westphalia, Germany

Otitis externa is the inflammation of the external ear canal distal to the tympanic membrane, a common multifactorial disease with prevalence in dogs as high as 10-20%. It is one of the most common reasons for small animal presentation to the veterinarian. The clinical signs include head shaking, pain, hyperthermia, erythema, odor and exudates. The causes are usually distinguished as primary, when a healthy animal/ear becomes diseased and secondary, with disease that is established in an abnormal ear. In most cases the infectious agents are responsible for the inflammation, commonly the association between bacteria and yeasts such as Malassezia pachydermatis. The aim of this study was to evaluate the etiology of otitis externa in dogs presented to a clinic in North Rhine-Westphalia region, Germany and test the susceptibility to antibiotics of the isolated strains. Between June 2016 and July 2018, a total of 39 dogs with clinical otitis externa were included in this study, and the same number of swabs used to collect cerumen and ear exudates were processed. The swabs were initially used to prepare slides and examine them after Gram staining technique was performed. The identification of bacteria was possible using Vitek® 2 compact 15 Biomerieux device. Malasssezia pachydermatis was identified using both microscopic examination and cultivation on modified Dixon agar. The susceptibility to antibiotics was evaluated using Kirby-Bauer disk diffusion test. The results demonstrated that Staphylococcus pdeudintermedius was the most common isolated bacteria, present in 22 from 39 samples (56.4%), followed by Pseudomonas aeruginosa in 5 samples (12.8%), Streptococcus spp. in 5 samples (12.8%), Bacillus spp. in 5 samples (12.8%), Escherichia coli in 3 samples (7.7%), Staphylococcus haemolyticus in 2 samples (5.1%), Pantotea agglomerans in 2 samples (5.1%) and Enterobacter cloacae in 1 sample (2.56%). Bacterial associations were identitied in 7 (18%) cases. Malassezia pachydermatis yeast was present in 18 from 39 samples (46.1%). Regarding antibiotic susceptibility, the most efficient antibiotics were represented by Enrofloxacin, Amoxicillin and clavulanic acid and Marbofloxacin, while the least efficient were Polymyxin B and Cefovecin. Keywords: otitis externa, dogs, antibiotic susceptibility.