In vitro photoinactivation of bovine mastitis related pathogens

• We investigate the ability of photodynamic inactivation to inactivate bacteria and algae.
• Methylene blue and red light alone had no microbicidal effects.
• S. dysgalactiae, S. aureus and C. bovis were inactivated after 30 s of PDI irradiation.
• S. agalactiae was inactivated after 120 s of PDI irradiation.
• P. zopfii was inactivated after 180 s of PDI irradiation.

BackgroundBovine mastitis is considered the most important disease of worldwide dairy industry. Treatment of this disease is based on the application intramammary antibiotic, which favors an increase in the number of resistant bacteria in the last decade. Photodynamic inactivation (PDI) has been investigated in different areas of Health Sciences, and has shown great potential for inactivating different pathogens, without any selection of resistant microorganisms. The objective of this study was to investigate the efficacy of PDI in the inactivation of pathogens associated with bovine mastitis.MethodsWe tested the effectiveness of PDI against antibiotic resistant strains, isolated from bovine mastitis, from the following species: Staphylococcus aureus, Streptococcus agalactiae, Streptococcus dysgalactiae, Corynebacterium bovis, and the alga Prototheca zopfii. Nine experimental groups were evaluated: control, no treatment; light only, irradiation of a red light-emitting diode (λ = 662 (20) nm) for 180 s; exposure to 50 μM methylene blue alone for 5 min; and PDI for 5, 10, 30, 60, 120 and 180 s.ResultsS. dysgalactiae, S. aureus, and C. bovis were inactivated after 30 s of irradiation, whereas S. agalactiae was inactivated after 120 s and P. zopfii at 180 s of irradiation.ConclusionThese results show that PDI can be an interesting tool for inactivating pathogens for bovine mastitis.