Evaluation of 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyl tetrazolium bromide method for assessing biofilm formation in vitro by Trichosporon spp

Background: Invasive infections due to Trichosporon spp. have increased recently and are frequently associated with indwelling medical devices. Such infections which are associated with biofilm formation do not respond to the routinely used antifungal agents and are often persistent, associated with high mortality rate. Various methods have been described by researchers to evaluate and quantify the biofilm formation.

Aim: This study was conducted to compare two methods of biofilm production by Trichosporon sp, i.e., test tube method with crystal violet (CV) staining and 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyl tetrazolium bromide (MTT) assay.

Materials and methods: Seventy-two clinical isolates of Trichosporon spp. collected from various sources were considered for the study. The identity of all the isolates was genotypically confirmed by Trichosporon-specific polymerase chain reaction (PCR). The isolates were further speciated phenotypically using biochemical profile and growth characteristics which identified the isolates as Trichosporon asahii (64/72), Trichosporon asteroides (5/72), Trichosporon cutaneum (2/72), and Trichosporon mucoides (1/72). Biofilm production was then evaluated and compared by test tube-CV method and MTT assay.

Results: All the Trichosporon isolates produced biofilm by MTT assay, whereas only 42 (53.6%) of the isolates were detected to be biofilm producers by CV method. Furthermore, MTT assay could differentiate better between weak and moderate biofilm producers as compared to CV method.

Conclusion: Hence, MTT assay is a reliable method for quantification of biofilm produced by Trichosporon spp. using 96-well microtiter plate.