In vitro susceptibility of Pythium insidiosum and a Lagenidium sp to itraconazole, posaconazole, voriconazole, terbinafine, caspofungin, and mefenoxam.
OBJECTIVE
To evaluate the radial growth assay for use in in vitro susceptibility testing of Pythium insidiosum and a Lagenidium sp and to assess susceptibility of representative isolates to itraconazole, posaconazole, voriconazole, terbinafine, caspofungin, and mefenoxam.


METHODS
6 isolates each of P insidiosum and Lagenidium sp.


METHODS
Isolates were plated in triplicate onto agar supplemented with antifungal compounds at concentrations of 0.025 to 8 microg/mL. Isolates on dimethyl sulfoxide- and water-supplemented agar served as control samples. Effect of antifungal concentration on colony diameter was assessed with a mixed linear model. Assay variability was assessed with the coefficient of variation.


RESULTS
Colony growth was uniform (mean intra-assay and interassay coefficients of variation were < 5%). Minimal inhibition was evident with voriconazole and posaconazole at 8 microg/mL. Terbinafine at 8 microg/mL significantly reduced growth of P insidiosum and at > or = 1 microg/mL significantly reduced growth of the Lagenidium sp. Caspofungin and mefenoxam (concentrations > or = 1 microg/mL and > or = 0.025 microg/mL, respectively) significantly reduced growth of both pathogens. Mefenoxam at 0.1 microg/mL caused > 50% growth inhibition in 11 of 12 isolates and at 1 microg/mL caused > 90% inhibition in all isolates.


CONCLUSIONS
Results suggested that the radial growth assay was a simple, reproducible technique for susceptibility testing of P insidiosum and a Lagenidium sp. Azoles had limited activity, whereas terbinafine and caspofungin caused significant but minimal to moderate inhibition. Only mefenoxam had a profound effect on both pathogens at concentrations likely to be achievable in tissues.
Brown
Tina A
TA
Department of Veterinary Clinical Sciences, School of Veterinary Medicine, Louisiana State University, Baton Rouge, LA 70803, USA.
Grooters
Amy M
AM
Hosgood
Giselle L
GL
D000409:Alanine / Q000031:analogs & derivatives / Q000494:pharmacology; D000890:Anti-Infective Agents / Q000494:pharmacology*; D000077336:Caspofungin; D054714:Echinocandins / Q000494:pharmacology; D066298:In Vitro Techniques; D017964:Itraconazole / Q000494:pharmacology; D044726:Lagenidium / Q000187:drug effects* / Q000254:growth & development; D055666:Lipopeptides; D008826:Microbial Sensitivity Tests; D009281:Naphthalenes / Q000494:pharmacology; D011743:Pyrimidines / Q000494:pharmacology; D011775:Pythium / Q000187:drug effects* / Q000254:growth & development; D000077291:Terbinafine; D014230:Triazoles / Q000494:pharmacology; D065819:Voriconazole
D000890:Anti-Infective Agents; D054714:Echinocandins; D055666:Lipopeptides; D009281:Naphthalenes; D011743:Pyrimidines; D014230:Triazoles; D017964:Itraconazole; C101425:posaconazole; D000077336:Caspofungin; C473256:mefenoxam; D000077291:Terbinafine; D065819:Voriconazole; D000409:Alanine