Pyomelanin Secretion in Madurella mycetomatis Interferes with Spectrophotometrically End-point Reading using the Sensititre™ YeastOne™ Alamar Blue Assay but not with Visual End-point Reading

The use of the Sensititre YeastOne YO10 alamarBlue assay for the in vitro susceptibility testing of Madurella mycetomatis was evaluated in M. mycetomatis isolates with and without pyomelanin secretion. Pyomelanin secretion did not influence visual endpoint reading; however, it caused a shift in peak absorbance from 570 nm to 620 nm when read spectrophotometrically. Therefore, when choosing the method for endpoint reading, the presence of pyomelanin should be considered.