Antimicrobial efficacy of in vitro and ex vivo photodynamic therapy using porphyrins against Moraxella spp. isolated from bovine keratoconjunctivitis.

Infectious bovine keratoconjunctivitis (IBK) is an ocular disease affecting bovine herds worldwide, and it causes significant economic loss. The etiologic agent of IBK is considered to be Moraxella bovis, but M. ovis and M. bovoculi are frequently recovered of animals presenting clinical signs of IBK. The therapeutic measures available for its control have limited efficacy. Antimicrobial photodynamic therapy (aPDT) using porphyrins as photosensitizing molecules is an alternative method that can be used to reduce microbial growth. We evaluated the antibacterial activity of aPDT using two water-soluble tetra-cationic porphyrins (H2TMeP and ZnTMeP) against 22 clinical isolates and standard strains of Moraxella spp. in vitro and in an ex vivo model. For the in vitro assay, 4.0 µM of porphyrin was incubated with approximately 1.0 × 104 CFU/mL of each Moraxella sp. isolate and exposed to artificial light for 0, 2.5, 5, and 7.5 min. Next, 50 µL of this solution was plated and incubated for 24 h until CFU measurement. For the ex vivo assay, corneas excised from the eyeballs of slaughtered cattle were irrigated with Moraxella spp. culture, followed by the addition of zinc(II) porphyrin ZnTMeP (4.0 µM). The corneal samples were irradiated for 0, 7.5, and 30 min, followed by swab collection, plating, and CFU count. The results demonstrated the in vitro inactivation of the strains and clinical isolates of Moraxella spp. after 2.5 min of irradiation using ZnTMeP, reaching complete inactivation until 7.5 min. In the ex vivo experiment, the use of ZnTMeP resulted in the most significant reduction in bacterial concentration after 30 min of irradiation. These results encourage future in vivo experiments to investigate the role of metalloporphyrin ZnTMeP in the inactivation of Moraxella spp. isolates causing IBK.

Isolation of Moraxella spp. from horses with conjunctivitis in Southern Brazil.

Infectious keratoconjunctivitis (IKC) is the most frequent ocular disease in livestock worldwide and is primarily caused by Moraxella bovis, M. ovis, and/or M. bovoculi. The economic impact of IKC is mainly due to ocular damage, which leads to weight loss, management difficulties, pain and discomfort, and cost of treatments. In horses, limited information is available on the association of Moraxella spp. with keratoconjunctivitis. The present report describes two cases of equine keratoconjunctivitis caused by members of the genus Moraxella. Both animals presented with lacrimation, conjunctivitis, photophobia, mucoid or purulent secretions, blepharitis, and conjunctival hyperemia. The diagnosis of IKC was based on the epidemiological and clinical findings; the etiological agent was identified through bacteriological (culture and biochemistry assays) and molecular testing (PCR and nucleotide sequencing). Our study reports the isolation of Moraxella bovoculi (SBP 88/19) and a putative new species/mutant of Moraxella (SBP 39/19) recovered from ocular secretions in horses. Thus, we suggest the inclusion of Moraxella spp. infection in the differential diagnosis of conjunctivitis in horses in Southern Brazil.

In vitro antimicrobial photodynamic therapy using tetra-cationic porphyrins against multidrug-resistant bacteria isolated from canine otitis.

Antimicrobial-resistant bacteria have been frequently isolated from canine otitis. Photodynamic therapy using porphyrins as photosensitizing molecules is an alternative therapy against microorganisms in localized infections. Therefore, we evaluated the antibacterial activity of two tetra-cationic porphyrins (H2TMeP and ZnTMeP) against gram-positive and -negative bacteria isolated from canine otitis, as well as its putative action mechanism. For this, two gram-positive and two gram-negative bacteria frequently detected in cases of canine otitis (coagulase-positive and -negative staphylococci [CPS and CNS], Pseudomonas aeruginosa, and Proteus mirabilis) were used in antibacterial activity assays. Each porphyrin at a non-cytotoxic dose was incubated with a fixed concentration of each bacterium and exposed to white-light irradiation for 0, 30, 60, and 90 min. Clinical isolates of CPS and CNS were photo-inactivated after 30 min of white-light exposure by both porphyrins (p < 0.05). Gram-negative bacteria were also photo-inactivated after 30 min (p < 0.05), reaching complete inactivation after 60 and 90 min of white-light irradiation by H2TMeP and ZnTMeP, respectively. Antibacterial assays using standard bacterial strains (ATCCs) demonstrated similar results to those obtained with clinical isolates, except for P. aeruginosa, which was completely inactivated by ZnTMeP at 60 min, and the absence of a significant reduction in P. mirabilis concentration when irradiated for 30 min. Similar assays were conducted using reactive oxygen species scavengers showing that the putative mechanism for bacterial inactivation is through the production of singlet oxygen species. These results indicated that H2TMeP and ZnTMeP tetra-cationic porphyrins were effective against bacteria isolated from canine otitis.