Andre Gratia and Sara Dath observed a fungal contamination in one of their Staphylococcus aureus cultures that was inhibiting the growth of the bacterium

In Belgium in 1920, Andre Gratia and Sara Dath observed a fungal contamination in one of their Staphylococcus aureus cultures that was inhibiting the growth of the bacterium. They identified the fungus as a species of Penicillium and presented their observations as a paper, but it received little attention. An Institut Pasteur scientist, Costa Rican Clodomiro Picado Twight, similarly recorded the antibiotic effect of Penicillium in 1923.