Abstract
Background:
Malassezia yeasts are part of the resident microbiota of canine skin and ear canal. The compromised immunity of animals, changes in environmental factors, and antibacterial treatment often result in their proliferation and subsequent complications.

Aim:
This single-center retrospective study was designed to investigate the prevalence of Malassezia spp. yeasts as agents of mono- and co-infections in dogs with clinical signs of inflammation referred to the University Veterinary Hospital, Stara Zagora in 2019-2023.

Methods:
Swab samples of ear, nasal, conjunctival, throat discharges, wound, abscess, and fistula discharges, and skin lesions fluid were collected from dogs with clinical inflammation using sterile cotton applicators, immediately transferred to Stuart transport medium, and inoculated on different culture media within 24 h. The presence of microorganisms was reported based on isolation in pure culture or as the predominant isolate in a mixed culture. The yeasts were identified by the specific growth morphology of colonies and cell morphology. Data analysis included the year of isolation, sampling site, and microbial pathogen genus. The differences in the prevalence of yeasts according to the sampling site were assessed using the chi-square test and test of independent proportions.

Results:
During 2019–2023, the microbiological examination of 896 swab samples from dogs with clinical signs of inflammation referred to the University Veterinary Hospital, Stara Zagora, resulted in 201 unique Malassezia pachydermatis identifications, including 189 from otitis and 12 from skin lesions. The 5-year prevalence of yeasts in dogs with ear infections was 60.19% (95% confidence interval 51.92-69.41%) and in dogs with skin infections was 4.11% (95% confidence interval 2.12-7.18%). M. pachydermatis was the only infectious agent in 32.3% of dogs with otitis. In 39.8% of cases, it was associated only with staphylococci, whereas polymicrobial infections were less frequently registered. In dogs with skin lesions, M. pachydermatis was always isolated together with a bacterial pathogen, most often staphylococci.

Conclusion:
The relatively constant presence of M. pachydermatis in canine clinical samples from otitis and skin infections implies that targeted testing for yeasts should not be omitted with regard to more accurate diagnosis of the etiological agents and successful treatment outcome.

Key words: Yeasts; Otitis; Skin lesions; Canine clinical samples.