Canine otitis externa is a common disorder in small animal practice with prevalence up to 20%. In a large percentage of cases, canine otitis externa is a chronic and recurrent disease also associated with drug-resistant bacteria that is difficult to treat with traditional antibiotics. Photodynamic therapy (PDT) is a new strategy to exterminate pathogenic microorganisms such as bacteria and fungi. The purpose of this study was to investigate the effectiveness of photodynamic therapy against canine otitis externa using three photosensitizer (PS); 5-Aminolevulinic acid (5-ALA) and Methyl aminolevulinic acid (MAL) with semiconductor laser diode (SLD, 635nm of wave length), Chlorophylllipoid complex (CLC) with light-emitting diode (LED, 660nm of wave length). After PDT, dogs showed improved Otitis Index Score (OTIS) in swelling, exudate, odor, and pain. A result of the cytology test revealed decrease of bacteria and malassezia count in the oil immersion field and colony forming units count. PDT was effective as a bacteriocide of methicillin-resistant Staphylococcus pseudintermedius (MRSP) and a fungicide of Malassezia pachydermatis. MAL and 5-ALA were more effective PS against canine otitis externa than CLC. These results suggest that PDT is a new strategy to exterminate pathogenic microorganisms such as bacteria and fungi. PDT can be considered as a new therapeutic approach for canine recurrent otitis externa and a countermeasure to drug resistance that is a disadvantage of traditional antibiotic and antifungal therapy.

Keywords: photodynamic therapy, 5-ALA, MAL, CLC, otitis externa, dog