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Bacterial agents are considered important pathogens causing external otitis in dogs. It is essential to carry out bacterial culture and antimicrobial susceptibility test in the case of otitis externa, particularly for chronic or recurring cases. Sterile swab samples were obtained from terminal part of vertical ear canals of 74 dogs with otitis externa for cytology, bacterial culture and antimicrobial susceptibility test. Cytologic smears were stained using Gram and Giemsa staining methods. Aerobic bacterial culture performed on blood agar and MacConkey agar. Among total number of 92 isolated bacteria, 68 were Staphylococcus intermedius. Other isolated bacteria included: Pseudomonas aeruginosa, Proteus mirabilis, Escherichia coli, Pasteurella canis, and six other species of coagulase-negative Staphylococcus. Antimicrobial susceptibility test were performed for all isolated bacteria using 14 antibiotics. Based on the results of this study, all isolated Staphylococcus spp. were sensitive to amikacin, enrofloxacin, and rifampin, and had low resistance to gentamicin, cephalothin and ceftriaxone. More than half of gram-positive isolates were resistant to penicillin and ampicillin. Generally, all isolated gram-negative bacteria, were sensitive to amikacin and enrofloxacin, and had low resistance to ceftriaxone and gentamicin. They were highly resistant to penicillin, eythromycin, and cephalothin. Regarding the results of this study, in cases of uncomplicated otitis externa, it is possible to select antimicrobial drugs merely based on cytology, but it is recommended to perform bacterial culture and antimicrobial susceptibility test. However, in complicated or refractory cases, antimicrobials should be selected based on bacterial culture and antimicrobial susceptibility test.

ABSTRACT. The yeasts of the Malassezia genus are opportunistic microorganisms in the skin and auricular canal of human and animals, mainly cats, and can cause otitis externa and dermatitis disorders. The aim of this study was to evaluate the occurrence of different species of Malassezia in the external ear canal of cats with and without otitis externa. Thirty-one normal cats and 82 animals with otitis externa were clinically examined. Sterile cotton swabs were used to collect specimens from the external ear canal and streaked onto the surface of Sabouraud dextrose agar (SDA) and modified Dixon agar. Malassezia yeasts were isolated from 95.1% and 48.4% of the cats with and without otitis externa, respectively. The rate of isolation in affected animals versus normals was highly significant (P<0.05). Out of the 137 isolates obtained from cats with otitis, 57.7% were identified as M. pachydermatis (with significant frequency; P<0.05), 15.4% as M. obtusa, 11.4% as M. globosa, 7.3% as M. slooffiae, 4.1% as M. sympodialis, 2.4% as M. furfur and 1.6% as M. restricta. Malassezia species were frequently isolated from subjects with age range from 1to 4 years old (42.7%). Our finding of Malassezia isolates indicated that feline otitis externa can be associated with lipid-dependent Malassezia species in addition to the non lipid-dependent species M. pachydermatis.