Cytological and microbiotic aspects of the diagnosis of otitis externa in dogs

The purpose of the study was to compare cytological samples from two consecutive swabs obtained from ear canals of dogs with otitis externa and to determine the minimum number of samples required to obtain up-to-date information on the degree of microbiological contamination of the affected ear canals. Samples were obtained using sterile applicators with a cotton tip, which were sequentially inserted into ear canal until slight resistance (the junction between vertical and horizontal parts of ear canal), after making a circular motion, the applicator was removed and the material from the tip was applied to the glass slide with rolling movements so that on each slide there were four single parallel smears — two from each ear of the dog. The slides were air dried for one hour and stained using the standard Diff-­Quick method. The actual counting was carried out at 1000 × magnification (at a high magnification field). Bacteria were differentiated according to their shape into cocci and bacilli. The numbers of bacteria and fungi in the two samples were compared using the Wilcoxon matched pair test. Qualitative agreement between two consecutive swabs was determined using the k-test. Among the studied animals, a breed predisposition to otitis externa was revealed in Cocker Spaniels and French Bulldogs, and an anatomical predisposition in animals with drooping auricles. There was no significant difference in the number of microorganisms present in two ear cytology samples taken consecutively from the same ear at the same site in the external auditory canal, and there was significant agreement between the results of two consecutive smears for the presence of cocci and rods. For yeast, the agreement was only moderate. The data obtained indicate that in cases of otitis externa in dogs, reproducibility of cytological pattern with a single sample of material, as a rule, reflects current stage of pathogenesis of the disease and provides the best opportunity to detect local proliferative activity of opportunistic microbiota and corresponding inflammatory response of the macroorganism.