FastFung: A novel medium for the culture and isolation of fastidious fungal species from clinical samples

https://doi.org/10.1016/j.mimet.2020.106108Get rights and content

Highlights

  • FastFung is a culture medium based on Schædler agar.

  • It allows the culture of clinical fungi, including fastidious ones.

  • Its performances are enhanced compared to the Sabouraud medium gold standard.

  • The FastFung medium can be used for both research and diagnostic studies.

Abstract

We developed a novel culture medium, referred to FastFung medium as suitable for the culture of clinical fungi, including fastidious ones, for both research and diagnostic studies. It is based on Schædler agar supplemented with many essential components for the growth of fastidious fungi. It also contains selective antibacterial agents for the inhibition of contaminant bacteria growth. In this preliminary study, the FastFung medium was compared to the gold standard Sabouraud medium for 98 fungal and 20 bacterial strains.

The fungal strain positive culture rate was 100% vs. 95% and the bacterial strain inhibition was 100% vs. 20%, for the FastFung and Sabouraud media, respectively. When compared to the Sabouraud medium on 120 clinical samples, the FastFung medium displayed both a higher fungal colonies count, and a lower culture contamination rate. Storage at 4 °C for 4 weeks did not alter the FastFung culture medium performances for the six isolates of Candida, Cryptococcus, and Penicillium tested.

These encouraging results suggest future development of using the FastFung medium in clinical mycology and in mycobiome characterization. Further prospective evaluation aiming at assessing whether implementing the FastFung medium in the routine workflow simplifies and strengthen fungal isolation capacities in the clinical laboratory is warranted.

Introduction

Fungal species are ubiquitous environmental organisms. They can be found in food, water, soil and also isolated from humans and animals samples (Praneenararat, 2014). They are often associated with human infectious diseases (Botnaru et al., 2014; Rodriguez and Ramos, 2014). Fungal microorganisms of clinical interest are mainly grouped into three classes: Ascomycota, Basidiomycota and Zygomycota (Gouba & Drancourt, 2015). Fungal infections are the current object of many studies (Praneenararat, 2014; Botnaru et al., 2014; Chen et al., 2011). The predominant clinical species is Candida albicans that is involved in the majority of opportunistic invasive fungal diseases (Vidya et al., 2016). Indeed, recent studies have pointed out C. albicans as a major cause of morbidity and mortality in critical care patients, as well as its involvement in other oropharyngeal diseases of the mouth, and digestive and vaginal tract in immunocompromised and antibiotic treated individuals (Huffnagle & Noverr, 2013). The genera Cryptococcus and Aspergillus also include many fungi involved in human infections (Botnaru et al., 2014; Geltner & Lass-Florl, 2016). Many fungal species are opportunistic pathogens; i.e. they are commensals when the host is healthy, and they become pathogenic when the host is immunocompromised and/or critically ill (Huffnagle & Noverr, 2013). Thus, the population of immunocompromised patients has the highest risk of opportunistic fungal infections (Botnaru et al., 2014; Rodriguez & Ramos, 2014; de Oliveira et al., 2014). Moreover, recent increases in emerging fungal infections call for an effective culture medium capable of timely isolating fastidious fungi from any biological sample at the clinical mycology laboratory.

While Sabouraud dextrose agar is the most frequently used medium for fungal isolation (Gumral et al., 2015; Matić Petrović et al., 2015), other media are commonly used for culture of yeasts and filamentous fungi, including Potatoe Dextrose Agar (Gouba et al., 2013), Czapek (Ali et al., 2014) and Dixon agar (Shah et al., 2013). These media are often used in combination in clinical laboratories. These, and several other culture media, are used as reference for the isolation or the identification of specific fungal taxa (Ben Salah et al., 2010). This study aimed at developing a novel culture medium, which is suitable for the culture of clinical fungi, including fastidious ones, for both research and diagnostic studies. The FastFung medium is based on Schædler agar (Sigma-Aldrich) supplemented with many components needed for the growth of fungal species. It also contains selective antibacterial agents for the inhibition of contaminant bacteria. In this preliminary study, the FastFung medium was evaluated on 98 fungal and 20 bacterial strains.

Section snippets

Culture media

In this study the performance of fungal culture on FastFung and Sabouraud dextrose agar (Oxoid, Dardilly, France) media were compared. The Sabouraud medium is supplemented with chloramphenicol and gentamycin. In addition to bacteriological agar, this culture medium contains glucose and peptone allowing the growth of many fungal species. Sabouraud medium was considered as the gold-standard fungal medium in this study. The FastFung medium proposed in this study is composed per liter of 43 g of

FastFung medium assessment on fungal strains

The positive culture rate of the fungal strains after 6 days 98/98 (100%) with the FastFung medium. Moreover, each inoculum dilution yielded a positive culture with the FastFung medium. Among each fungal strain assayed on the FastFung medium, growth was visualized in 57/98 (58%) of the cultures after 24 h of incubation and in 67/98 (68%) after 48 h of incubation. In contrast, the Sabouraud medium allowed the growth of 93/98 (95%) of the fungal strains, and in particular, Candida zeylanoides,

Discussion

Overall the FastFung medium proved more efficient than the Sabouraud medium for the rapid isolation of fungi and inhibition of bacteria and filamentous fungi contaminants from the clinical samples tested. Each of the 98 fungal strains tested grew on the FastFung medium, whereas only 67 grew on Sabouraud. A number of fastidious fungi, such as the lipid dependent Malassezia spp. yeast, require the specific culture media for their growth (Shah et al. 2013, Ben Salah et al. 2010). The addition of

Ethical approval

Not required.

Funding information

This work was supported by the French Government under the «Investissements d'avenir » (Investments for the Future) program managed by the Agence Nationale de la Recherche (ANR, fr: National Agency for Research), (reference: Méditerranée Infection 10-IAHU-03).

This work was supported by Région Provence-Alpes-Côte d'Azur and European funding FEDER (fonds européen de développement régional) PRIMMI ((Plateformes de Recherche et d'Innovation Mutualisées Méditerranée Infection).

Declaration of Competing Interest

None of the authors have competing interest to declare.

Acknowledgements

This work is dedicated to the memory of Marcel Sy (PhD student died on 15 September 2016); Marcel Sy has made a substantial contribution to this work.

References (21)

There are more references available in the full text version of this article.

Cited by (7)

View all citing articles on Scopus
View full text