INTRODUCTION Microbial dysbiosis is an important secondary factor in canine otitis externa (Nuttall, 2023). We have long observed, both by routine cytological examinations and prospective semi-quantitative culture, that Malassezia yeast overgrowth (a fungal dysbiosis) frequently follows successful topical antibacterial therapy of refractory canine bacterial otitis when using potent broad-spectrum drugs such as enrofloxacin and especially piperacillin-tazobactam (PT) (Juhola et al., 2025).