Evaluation of Liofilchem Derma-SR-Screen 4-Well Agar Panels in Screening of Terbinafine and Itraconazole Susceptibility in Clinical Trichophyton Isolates

The aim of this paper is to evaluate the performance of the Derma-SR-screen agar for accurate discrimination between susceptible and non-susceptible clinical Trichophyton isolates. Consecutive Trichophyton isolates, received for identification and susceptibility testing, were screened for terbinafine and itraconazole resistance using Liofilchem Derma-SR-screen 4-well panels alongside EUCAST reference testing (E.Def 11.0). EUCAST tentative ECOFFs (terbinafine: T. rubrum 0.03 mg/L; T. indotineae 0.125 mg/L; itraconazole: both species: 0.25 mg/L) were applied for wild-type/non-wild-type classification. Plates were evaluated after 5 days of incubation at 25 °C, with growth graded 0-+++. Faint growth (+) was disregarded. All isolates underwent sqle sequencing. Forty isolates were included; 25 were non-wild-type harbouring Sqle alterations (F397I (number (n) = 1), F397L (n = 17), L393F (n = 3), L393S (n = 1), and Q408L (n = 3)). On day 5, 21 isolates reached +++ growth in the control well; a further 10 reached this level on day 6. The remaining isolates reached a ++/+++ score after 5/6 days (n = 7/n = 2). The 0.125 mg/L terbinafine agar correctly identified 7/8 non-wild-type T. indotineae isolates (4/5 F397L and 3/3 Q408L alterations), all 17 non-wild-type and eight wild-type T. rubrum isolates, as well as the five wild-type isolates of other Trichophyton spp. The 0.016 mg/L agar correctly identified all 17 non-wild-type T. rubrum isolates, but misclassified 2/8 wild-type isolates as non-wild-type. All isolates were wild-type to itraconazole and correctly identified. The Derma-SR-screen agar resulted in correct classification of 24/25 (96%) sqle mutant T. indotineae and T. rubrum isolates. Two wild-type T. rubrum isolates grew at the 0.016 mg/L terbinafine agar suggesting possible reduced agar potency at this concentration.