The green colour effect (GCE) of the killer strain Cryptococcus laurentii CBS 139 on Staib agar.

Attention is drawn to the observation that the type strain Cryptococcus laurentii CBS 139, producing killer toxins (mycocins) directed at Cr. neoformans var. gattii, causes a green colour effect (GCE) on Staib agar (Guizotia abyssinica creatinine agar) in combination with an intense assimilation of creatinine. Five (9.6%) out of 52 strains of Cr. laurentii of various origin, showed a GCE and intense creatinine assimilation. Further research must show if all Cr. laurentii strains, characterized by a GCE similar to that of the strain CBS 139, are also capable of producing killer toxins. For further ecological and epidemiological research on strains producing killer toxins directed against species of the genus Cryptococcus, it is proposed to use Staib agar as differential culture medium indicating both colour effects, i.e. the GCE and the brown colour effect (BCE).