Today's Veterinary Practice

MAY-JUN 2017

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63 MAY/JUNE 2017 ■ TVPJOURNAL.COM DERMATOLOGY DETAILS of topical therapy. Cytologic samples should be collected gently from the horizontal canal. Exudate samples can be smeared onto a slide with mineral oil to look for mites. The most common type of coccoid bacteria found in the ears of dogs with otitis externa is Staphylococcus pseudintermedius, and the most common type of rod bacteria is Pseudomonas aeruginosa. 1–6 Malassezia species are also common organisms 1–5 ( Figure 4 ). It is important to describe the presence of any inflammatory or neoplastic cells as well as quantify each type of bacteria and yeast per oil immersion field (100×) to establish severity and allow monitoring at future visits. In one study, mean bacterial counts per high-power dry field of ≥25 and mean Malassezia counts per high-power dry field of ≥5 were considered abnormal in the external ear canals of dogs. 5 Leukocytes are always abnormal, and bacteria in the presence of leukocytes signal infection. Bacterial Culture and Sensitivity Culture and sensitivity (C/S) may be useful in identifying specific otic pathogens and assisting with treatment decisions; however, a limitation is that antibiotic sensitivity data reflect the serum level needed systemically and may not predict true susceptibility of otic topical antibiotics. Typical indications for bacterial C/S include the following 1–4 : • Chronic otitis associated with bacteria (cocci [ Figure 5 ] and/or rods) seen on cytology • Rods seen on cytology ( Figure 6 ) • Suspected or confirmed cases of otitis media (systemic therapy may be indicated) • History of multidrug-resistant bacteria • History of long-term oral or topical antibiotic therapy • Bacteria persisting on cytology despite apparently appropriate therapy Cytology should always be performed before aerobic C/S to assist with interpretation of results and identification of concurrent problems. In one study, 7 however, cytologic results agreed with culture results only 68% of the time. The same study 7 showed that different bacterial organisms were isolated from the same ear in 20% of the FIGURE 6. Cytologic appearance of degenerate neutrophils and rods (high-power oil immersion field 100× objective). FIGURE 4. Cytologic appearance of Malassezia species (high-power oil immersion field 100× objective). FIGURE 5. Cytologic appearance of degenerate neutrophils and cocci (high-power oil immersion field 100× objective).

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