Evaluation of ID Fungi Plates Medium for Identification of Molds by MALDI Biotyper

Abstract

MALDI-TOF mass spectrometry (MS) identification of pathogenic filamentous fungi is often impaired by difficulties in harvesting hyphae embedded in the medium and long extraction protocols. The ID Fungi Plate (IDFP) is a novel culture method developed to address such difficulties and improve the identification of filamentous fungi by MALDI-TOF MS. We cultured 64 strains and 11 clinical samples on IDFP, Sabouraud agar-chloramphenicol (SAB), and ChromID Candida agar (CAN2). We then compared the three media for growth, ease of harvest, amount of material picked, and MALDI-TOF identification scores after either rapid direct transfer (DT) or a long ethanol-acetonitrile (EA) extraction protocol. Antifungal susceptibility testing and microscopic morphology after subculture on SAB and IDFP were also compared for ten molds. Growth rates and morphological aspects were similar for the three media. With IDFP, harvesting of fungal material for the extraction procedure was rapid and easy in 92.4% of cases, whereas it was tedious on SAB or CAN2 in 65.2% and 80.3% of cases, respectively. The proportion of scores above 1.7 (defined as acceptable identification) were comparable for both extraction protocols using IDFP (P = 0.256). Moreover, rates of acceptable identification after DT performed on IDFP (93.9%) were significantly higher than those obtained after EA extraction with SAB (69.7%) or CAN2 (71.2%) (P = <0.001 and P = 0.001, respectively). Morphological aspects and antifungal susceptibility testing were similar between IDFP and SAB. IDFP is a culture plate that facilitates and improves the identification of filamentous fungi, allowing accurate routine identification of molds with MALDI-TOF-MS using a rapid-extraction protocol.

Keywords: MALDI-TOF MS; culture media; culture plates; filamentous fungi; identification.

FIG 1

Distribution of cultural characteristics after culture on IDFP, SAB, or CAN2. IDFP, ID fungi plates (Conidia, Lyon, France); SAB, Sabouraud agar with chloramphenicol (Becton, Dickinson GmbH, Heidelberg, Germany); CAN2, ChromID Candida agar (bioMérieux, Marcy-l’Etoile, France).

FIG 2

Distribution of scores above 1.7 by culture plate and extraction protocol. Red plus signs correspond to means. Lines through boxes correspond to medians. Scores were significantly higher after EA than after DT on IDFP and SAB (P = 0.021 and 0.016, respectively). Scores after DT were significantly higher on IDFP than on SAB (P = 0.008). Scores after EA were significantly higher on IDFP than on SAB or CAN2 (P = 0.033 and 0.005, respectively). NS, nonsignificant differences.