A guide to the use of bioassays in exploration of natural resources

Bioassays are the main tool to decipher bioactivities from natural resources thus their selection and quality are critical for optimal bioprospecting. They are used both in the early stages of compounds isolation/purification/identification, and in later stages to evaluate their safety and efficacy. In this review, we provide a comprehensive overview of the most common bioassays used in the discovery and development of new bioactive compounds with a focus on marine bioresources. We present a comprehensive list of practical considerations for selecting appropriate bioassays and discuss in detail the bioassays typically used to explore antimicrobial, antibiofilm, cytotoxic, antiviral, antioxidant, and anti-ageing potential. The concept of quality control and bioassay validation are introduced, followed by safety considerations, which are critical to advancing bioactive compounds to a higher stage of development. We conclude by providing an application-oriented view focused on the development of pharmaceuticals, food supplements, and cosmetics, the industrial pipelines where currently known marine natural products hold most potential. We highlight the importance of gaining reliable bioassay results, as these serve as a starting point for application-based development and further testing, as well as for consideration by regulatory authorities.

Antifungal Susceptibility Testing: Current Approaches

Although not as ubiquitous as antibacterial susceptibility testing, antifungal susceptibility testing (AFST) is a tool of increasing importance in clinical microbiology laboratories. The goal of AFST is to reliably produce MIC values that may be used to guide patient therapy, inform epidemiological studies, and track rates of antifungal drug resistance. There are three methods that have been standardized by standards development organizations: broth dilution, disk diffusion, and azole agar screening for Aspergillus Other commonly used methods include gradient diffusion and the use of rapid automated instruments. Novel methodologies for susceptibility testing are in development. It is important for laboratories to consider not only the method of testing but also the interpretation (or lack thereof) of in vitro data.

Diagnosis of Candida albicans: conventional diagnostic methods compared to the loop-mediated isothermal amplification (LAMP) assay

Candida species cause a wide range of opportunistic infections in humans and animals. The detection of Candida species by conventional diagnosis methods is costly and time consuming. This study was conducted for the first time to evaluate and compare a relatively new molecular assay and the loop-mediated isothermal amplification (LAMP) technique with conventional methods for detection of Candida albicans. In this study, 70 different species of Candida identified by conventional methods were cultured on Sabouraud chloramphenicol agar medium and then the genomic DNA was extracted. The LAMP technique was performed using specific primers targeting the ITS2 gene of C. albicans. The analytical sensitivity and specificity of LAMP were measured using a tenfold serial dilution prepared from extracted DNA from standard C. albicans strain from 1 ng to 1 fg and the DNA samples of other clinical Candida species and three non-Candida yeast. Out of 70 yeast samples analyzed by LAMP technique, 24 samples (34.3%) were positive for C. albicans. Comparison of the results showed that the CHROMagar Candida and germ tube production methods are quite consistent with the LAMP technique, while the agreement amount between the results of carbohydrate assimilation and chlamydoconidia generation assays and LAMP technique was 98.5% and 72.8%, respectively. The detection limits of the LAMP assay were 10 fg of the DNA from the standard C. albicans strain. No amplification was observed in the DNA samples of other yeast species and only the DNA sample of standard C. albicans strain was amplified. Based on the results, it can be concluded that the LAMP method is as specific and precise as common diagnostic methods, but is faster, easier deployable or more sensitive. Therefore, this method can be used as a suitable complementary assay for Candida diagnosis in medical diagnostic laboratories and field conditions.

Antifungal drug resistance among Candida species: mechanisms and clinical impact

The epidemiology of Candida infections has changed in recent years. Although Candida albicans is still the main cause of invasive candidiasis in most clinical settings, a substantial proportion of patients is now infected with non-albicans Candida species. The various Candida species vary in their susceptibility to the most commonly used antifungal agents, and the intrinsic resistance to antifungal therapy seen in some species, along with the development of acquired resistance during treatment in others, is becoming a major problem in the management of Candida infection. A better understanding of the mechanisms and clinical impact of antifungal drug resistance is essential for the efficient treatment of patients with Candida infection and for improving treatment outcomes. Herein, we report resistance to the azoles and echinocandins among Candida species.

The future of fungal susceptibility testing

ABSTRACT 

The antifungal treatment failures and the emergence of resistant fungal strains have stimulated the need for reproducible and clinically relevant antifungal susceptibility testing (AFST). While the standard reference methods are not intended for routine use, commercial methods are widely used for performing AFST. However, to accelerate AFST and to improve the detection of antifungal resistance, which is the most challenging goal of AFST, novel assays have been developed. Following brief drug exposures of fungal cells, the new antifungal susceptibility end points seem to provide a reliable means of identifying fungal isolates, which harbor mutations that have been associated with antifungal resistance. This article summarizes the recent progress in AFST that is destined to enhance its clinical utility in the near future.