The laboratory diagnosis of Pythium insidiosum can be difficult by standard mycologic techniques. If molecular techniques are not available then susceptibility testing to minocycline or tigeccycline can be helpful in identifying the isolate.
Culture: aseptate hyaline fungus not meeting criteria for Mucor, Aspergillus or other common fungi
Pythium insidiosum is susceptible to minocycline and tigecycline. Demonstration that the organism is inhibited by these drugs differentiates Pythium from other filamentous fungi..
Tondolo et al used a 30 microgram minocycline disk to identify a fungal culture on routine agar (Sabouraud, Mueller Hinton, etc). Failure of the isolate to grow around the disk after 7 days at 35°C is evidence of Pythium insidiosum.
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