Biofilms of Candida spp. from the ocular conjunctiva of horses with reduced azole susceptibility: a complicating factor for the treatment of keratomycosis?

The research article is about a study on the ability of Candida species to form biofilms on the ocular surface of horses, and the role of this biofilm formation in complicating the treatment of fungal eye infections in horses.

Objectives and Methods of the Research

• The study aimed at assessing the biofilm-forming capacity of 15 strains of Candida species isolated from horses’ ocular conjunctiva.
• The biofilm-forming ability was evaluated by a method called crystal violet staining, which helps visualize the fungal biomass sticking onto polystyrene plates, and through scanning electron microscopy for detailed inspection.
• The researchers determined the minimum inhibitory concentrations (MICs) of four antifungal drugs (amphotericin B, fluconazole, itraconazole, and caspofungin) that are required to inhibit the growth of the strains in a free-floating (planktonic) state.
• Then, they evaluated the susceptibility of fully formed biofilms to these antifungal drugs by checking their metabolic activity after exposure to the drugs. This was done using the XTT oxidoreduction indicator.
• Data collected were subjected to statistical analysis through ANOVA and Tukey’s post-test. P-values less than 5% were considered to have a significant result.

Key Findings of the Research

• From the 15 strains tested, eight were capable of producing biofilms. They were categorized into strong (1 strain), moderate (3 strains), and weak (4 strains) producers based on the amount of crystal violet retained by the fungal biomass.
• The metabolic activity of one C. tropicalis biofilm was found not to decrease even after exposure to the tested antifungal drugs, implying that it is resistant to these medications.
• Of the eight biofilm-producing strains, the metabolic activities of five were reduced when exposed to amphotericin B, but not to the other drugs.
• Significant reduction in metabolic activity after exposure to fluconazole, itraconazole, and caspofungin, but not to amphotericin B, was found in one strain of C. parapsilosis sensu stricto and one C. glabrata.

Conclusions Drawn from the Research

• The findings of the study illustrate that Candida from horses’ ocular conjunctiva can form biofilms.
• As biofilms generally make the fungi more resilient to treatment, the results suggest these biofilms can contribute to complications in the treatment of horses’ fungal keratitis (a fungal infection of the eye).