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Adenylate cyclase toxin (ACT) is one of the principal virulence factors secreted by the whooping cough causative bacterium Bordetella pertussis, and it has a critical role in colonization of the respiratory tract and establishment of the disease. ACT targets phagocytes via binding to the CD11b/CD18 integrin and delivers its N-terminal adenylate cyclase (AC) domain directly to the cell cytosol, where it catalyzes unregulated conversion of cytosolic ATP into cAMP upon activation by binding to cellular calmodulin. High cAMP levels disrupt bactericidal functions of the immune cells, ultimately leading to cell death. In spite of its relevance in the ACT biology, the mechanism by which its ≈400 amino acid-long AC domain is transported through the target plasma membrane, and is released into the target cytosol, remains enigmatic. This article is devoted to refresh our knowledge on the mechanism of AC translocation across biological membranes. Two models, the so-called “two-step model” and the recently-proposed “toroidal pore model”, will be considered.

Background Malassezia pachydermatis is part of the skin microbiota of dogs and cats. M. pachydermatis has been associated with external otitis and seborrhoeic dermatitis, reported more often in dogs than in cats. When the physical, chemical or immunological mechanisms of the skin are altered, M. pachydermatis could act as a pathogen. Thus, several virulence factors, such as the ability to produce esterase, lipase, lipoxygenase, protease, chondroitin sulphatase, and hyaluronidase, have been studied. Aims In the present study, we aim to identify the phospholipase activity measured at pH 6.3, and the proteinase activity measured at pH 6.3 and pH 6.8 (pH from ears of dogs with external otitis) of M. pachydermatis strains isolated from dogs with and without external otitis. Methods The phospholipase activity was measured using a semi-quantitative method with egg yolk, and the proteinase activity with a semi-quantitative method using bovine serum albumin agar. The study was performed on 96 isolates of M. pachydermatis, 43 isolated from dogs without clinical symptoms of otitis, and 52 isolated from dogs with otitis. Results In our study, 75.8% of the isolates showed phospholipase activity at pH 6.3, and 81 and 97.9% of them showed proteinase activity measured at pH 6.3 and 6.8, respectively. A higher phospholipase activity was detected in strains isolated from dogs with otitis. The proteinase activity was increased at a pH of 6.8 (97.9%) in comparison to a pH of 6.3 (81%). Conclusions Our results suggest that the phospholipase activity may play an important role in the invasion of host tissues in chronic canine otitis cases. The proteinase activity results obtained in this study suggest that a reduction in the pH of the treatment may improve its efficacy in the resolution of M. pachydermatis otitis., Antecedentes Malassezia pachydermatis forma parte de la microbiota cutánea de perros y gatos. M. pachydermatis se ha asociado frecuentemente a otitis externa y dermatitis seborreicas, sobre todo en el perro, y con menor frecuencia en el gato. M. pachydermatis podría actuar como patógeno cuando existen alteraciones en los mecanismos físicos, químicos o inmunológicos de la piel. Se han identificado diversos factores de virulencia como la capacidad de producir estearasas, lipasas, lipooxigenasas, proteinasas, condroitinsulfatasas e hialuronidasas. Objetivos Se ha estudiado la actividad fosfolipasa medida a pH 6,3 y la actividad proteinasa medida a pH 6,3 y pH 6,8 (pH de oídos de perros con otitis) de cepas de M. pachydermatis aisladas de perros con otitis y sin otitis. Métodos Se ha estudiado la actividad fosfolipasa mediante un método semicuantitativo con yema de huevo y la actividad proteinasa mediante un método semicuantitativo con agar albúmina sérica bovina. Se ha realizado el estudio en 96 aislamientos de M. pachydermatis, 43 de ellos aislados de perros sin sintomatología clínica de otitis y 52 aislados de perros con otitis. Resultados Se observó que el 75,8% de los aislamientos presentaron actividad fosfolipasa a pH 6,3 y el 81% presentaron actividad proteinasa medida a pH 6,3, y el 97,9% a pH 6,8. Se detectó una mayor actividad fosfolipasa en cepas aisladas de perros con otitis. Con respecto a la actividad proteinasa, esta fue mayor a pH 6,8. Conclusiones Estos hallazgos sugieren que la actividad fosfolipasa podría jugar un papel importante en la invasión de los tejidos del hospedador, por lo menos en la otitis crónica canina. Con respecto a la actividad proteinasa, estos hallazgos podrían ayudar a mejorar la terapéutica de la otitis cuando está implicada M. pachydermatis en el proceso, ajustando a pH bajos los tratamientos aplicados. Antecedentes Malassezia pachydermatis forma parte de la microbiota cutánea de perros y gatos. M. pachydermatis se ha asociado fr