Extrusion of fluorescein diacetate by multidrug-resistant Candida albicans

Fluorescent toys 'n' tools lighting the way in fungal research

Although largely overlooked compared to bacterial infections, fungal infections pose a significant threat to the health of humans and other organisms. Many pathogenic fungi, especially Candida species, are extremely versatile and flexible in adapting to various host niches and stressful situations. This leads to high pathogenicity and increasing resistance to existing drugs. Due to the high level of conservation between fungi and mammalian cells, it is hard to find fungus-specific drug targets for novel therapy development. In this respect, it is vital to understand how these fungi function on a molecular, cellular as well as organismal level. Fluorescence imaging allows for detailed analysis of molecular mechanisms, cellular structures and interactions on different levels. In this manuscript, we provide researchers with an elaborate and contemporary overview of fluorescence techniques that can be used to study fungal pathogens. We focus on the available fluorescent labelling techniques and guide our readers through the different relevant applications of fluorescent imaging, from subcellular events to multispecies interactions and diagnostics. As well as cautioning researchers for potential challenges and obstacles, we offer hands-on tips and tricks for efficient experimentation and share our expert-view on future developments and possible improvements.

Genomic and proteomic dissection of the ubiquitous plant pathogen, Armillaria mellea: toward a new infection model system

Armillaria mellea is a major plant pathogen. Yet, no large-scale “-omics” data are available to enable new studies, and limited experimental models are available to investigate basidiomycete pathogenicity. Here we reveal that the A. mellea genome comprises 58.35 Mb, contains 14473 gene models, of average length 1575 bp (4.72 introns/gene). Tandem mass spectrometry identified 921 mycelial (n = 629 unique) and secreted (n = 183 unique) proteins. Almost 100 mycelial proteins were either species-specific or previously unidentified at the protein level. A number of proteins (n = 111) was detected in both mycelia and culture supernatant extracts. Signal sequence occurrence was 4-fold greater for secreted (50.2%) compared to mycelial (12%) proteins. Analyses revealed a rich reservoir of carbohydrate degrading enzymes, laccases, and lignin peroxidases in the A. mellea proteome, reminiscent of both basidiomycete and ascomycete glycodegradative arsenals. We discovered that A. mellea exhibits a specific killing effect against Candida albicans during coculture. Proteomic investigation of this interaction revealed the unique expression of defensive and potentially offensive A. mellea proteins (n = 30). Overall, our data reveal new insights into the origin of basidiomycete virulence and we present a new model system for further studies aimed at deciphering fungal pathogenic mechanisms.

New high-throughput screening assay to reveal similarities and differences in inhibitory sensitivities of multidrug ATP-binding cassette transporters

Cdr1p is the major ATP-binding cassette multidrug transporter conferring resistance to azoles and other antifungals in Candida albicans. In this study, the identification of new Cdr1p inhibitors by use of a newly developed high-throughput fluorescence-based assay is reported. The assay also allowed monitoring of the activity and inhibition of the related transporters Pdr5p and Snq2p of Saccharomyces cerevisiae, which made it possible to compare its performance with those of previously established procedures. A high sensitivity, resulting from a wide dynamic range, was achieved upon high-level expression of the Cdr1p, Pdr5p, and Snq2p transporters in an S. cerevisiae strain in which the endogenous interfering activities were further reduced by genetic manipulation. An analysis of a set of therapeutically used and newly synthesized phenothiazine derivatives revealed different pharmacological profiles for Cdr1p, Pdr5p, and Snq2p. All transporters showed similar sensitivities to M961 inhibition. In contrast, Cdr1p was less sensitive to inhibition by fluphenazine, whereas phenothiazine selectively inhibited Snq2p. The inhibition potencies measured by the new assay reflected the ability of the compounds to potentiate the antifungal effect of ketoconazole (KTC), which was detoxified by the overproduced transporters. They also correlated with the 50% inhibitory concentration for inhibition of Pdr5p-mediated transport of rhodamine 6G in isolated plasma membranes. The most active derivative, M961, potentiated the activity of KTC against an azole-resistant CDR1-overexpressing C. albicans isolate.

Fluconazole susceptibility testing of Candida species by flow cytometry

OBJECTIVE

Currently, antifungal drug susceptibility testing is labor-intensive, limited by delays in obtaining results and high costs. The purpose of this study was to determine the usefulness of flow cytometry (FCM) antifungal drug susceptibility testing as a routine laboratory procedure.

METHODS

A total of 24 clinical isolates of Candida spp. and reference strains were tested for susceptibility to fluconazole by FCM using propidium iodide (PI) as an indicator of viability. The minimum inhibitory concentration (MIC) was defined as the lowest concentration of fluconazole that resulted in an increase of 30% in mean channel fluorescence (MCF), compared to the growth control. FCM results were compared with MIC results as determined by the Clinical and Laboratory Standards Institute (CLSI) method.

RESULTS

An 8h incubation was sufficient for determination of the MICs. The results by FCM at 8h and the NCCLS methods at 24h showed 87.5% agreement to within two drug dilutions. However, the FCM method is labor-intensive in proportion to the larger number of samples. For Candida lusitaniae, MICs by the FCM method showed poor correlation with the CLSI method.

CONCLUSIONS

Further evaluation is necessary to assess the usefulness of FCM as a technique for routine antifungal MIC testing in the clinical laboratory.