Evaluation of disk diffusion method compared to broth microdilution for antifungal susceptibility testing of 3 echinocandins against Aspergillus spp

Sustained Release of Voriconazole Using 3D-Crosslinked Hydrogel Rings and Rods for Use in Corneal Drug Delivery

Corneal disorders and diseases are prevalent in the field of clinical ophthalmology. Fungal keratitis, one of the major factors leading to visual impairment and blindness worldwide, presents significant challenges for traditional topical eye drop treatments. The objective of this study was to create biocompatible 3D-crosslinked hydrogels for drug delivery to the cornea, intending to enhance the bioavailability of ophthalmic drugs. Firstly, a series of flexible and porous hydrogels were synthesized (free-radical polymerization), characterized, and evaluated. The materials were prepared by the free-radical polymerization reaction of 1-vinyl-2-pyrrolidinone (also known as N-vinylpyrrolidone or NVP) and 1,6-hexanediol dimethacrylate (crosslinker) in the presence of polyethylene glycol 1000 (PEG-1000) as the porogen. After the physicochemical characterization of these materials, the chosen hydrogel demonstrated outstanding cytocompatibility in vitro. Subsequently, the selected porous hydrogels could be loaded with voriconazole, an antifungal medication. The procedure was adapted to realize a loading of 175 mg voriconazole per ring, which slightly exceeds the amount of voriconazole that is instilled into the eye via drop therapy (a single eye drop corresponds with approximately 100 mg voriconazole). The voriconazole-loaded rings exhibited a stable zero-order release pattern over the first two hours, which points to a significantly improved bioavailability of the drug. Ex vivo experiments using the established porcine eye model provided confirmation of a 10-fold increase in drug penetration into the cornea (after 2 h of application of the hydrogel ring, 35.8 ± 3.2% of the original dose is retrieved from the cornea, which compares with 3.9 ± 1% of the original dose in the case of eye drop therapy). These innovative hydrogel rods and rings show great potential for improving the bioavailability of ophthalmic drugs, which could potentially lead to reduced hospitalization durations and treatment expenses.

Secreted Enzyme-Responsive System for Controlled Antifungal Agent Release

Essential oil components (EOCs) such as eugenol play a significant role in plant antimicrobial defense. Due to the volatility and general reactivity of these molecules, plants have evolved smart systems for their storage and release, which are key prerequisites for their efficient use. In this study, biomimetic systems for the controlled release of eugenol, inspired by natural plant defense mechanisms, were prepared and their antifungal activity is described. Delivery and antifungal studies of mesoporous silica nanoparticles (MSN) loaded with eugenol and capped with different saccharide gates—starch, maltodextrin, maltose and glucose—against fungus Aspergillus niger—were performed. The maltodextrin- and maltose-capped systems show very low eugenol release in the absence of the fungus Aspergillus niger but high cargo delivery in its presence. The anchored saccharides are degraded by exogenous enzymes, resulting in eugenol release and efficient inhibition of fungal growth.

Development and multicentre validation of an agar-based screening method for echinocandin susceptibility testing of Aspergillus species

BACKGROUND

Reference antifungal susceptibility testing of echinocandins against Aspergillus spp. relies on the determination of the minimal effective concentration, which is difficult to perform, time-consuming and subjective. We developed and evaluated in a multicentre study an agar-based screening method for echinocandin susceptibility testing of Aspergillus spp.

METHODS

Forty WT isolates [10 Aspergillus fumigatus species complex (SC), 10 Aspergillus flavus SC, 10 Aspergillus terreus SC and 10 Aspergillus niger SC] and 4 non-WT A. fumigatus isolates with or without known fks alterations were used. The optimal test conditions and stability over time were evaluated in preliminary studies monitoring colony growth. Twenty-microlitre aliquots of 1-2 McFarland inocula in 0.1% Tween 20 aqueous solution were added to each well and plates were incubated for 24/48 h at 35 ± 2°C. Subsequently, all isolates were tested blindly at three centres using four-well screening plates, containing anidulafungin, caspofungin, micafungin or no antifungal in each of the four wells, respectively.

RESULTS

WT isolates produced fluffy colonies on drug-free agar wells only. The non-WT isolates produced fluffy colonies on echinocandin-containing and control agar wells. Using the echinocandin concentrations of 0.25 mg/L anidulafungin, 1 mg/L caspofungin and 0.125 mg/L micafungin, and the compact (non-fluffy) versus fluffy colony morphology endpoint, all centres successfully discriminated non-WT and WT strains even after 24 h. Among the three echinocandins, anidulafungin produced the clearest endpoints.

CONCLUSIONS

The four-well plate agar method is suitable for echinocandin susceptibility screening of Aspergillus spp. and can be used to detect echinocandin non-WT isolates.

Updating of in vitro antifungal susceptibility tests

Fungal diseases, including those caused by (multi)drug-resistant fungi, still represent a global public health concern. Information on the susceptibility of these microorganisms to antifungal agents must be quickly produced to help clinicians initiate appropriate antifungal therapies. Unfortunately, antifungal susceptibility tests are not as developed or widely implemented as antibacterial tests, being similar in design, accuracy and reproducibility, but also laborious and slow. In this article, we review the methods of in vitro susceptibility testing, both reference (CLSI and EUCAST), commercial and new methods based on proteomics (MALDI-TOF MS) and in the detection of resistance genes by nucleic acid amplification techniques. In addi-tion, we discuss the newly established clinical breakpoints, as well as the epidemiological cut-off points, which constitute a new category that can help in the early identification of isolates that have acquired resistance mechanisms. We also discuss the advantages and limitations of each of the methods studied. Therefore, we can conclude that, although there has been much progress in studies of in vitro susceptibility testing to antifungals, there are still limitations in its application in the daily routine of microbiology labo-ratories, although it seems that the future is promising with the new technologies based on proteomics and nucleic acid amplification. Supplement information: This article is part of a supplement entitled «SEIMC External Quality Control Programme. Year 2016», which is sponsored by Roche, Vircell Microbiologists, Abbott Molecular and Francisco Soria Melguizo, S.A. © 2019 Elsevier España, S.L.U. and Sociedad Española de Enfermedades Infecciosasy Microbiología Clínica. All rights reserved.

Study of Pathogens of Fungal Keratitis and the Sensitivity of Pathogenic Fungi to Therapeutic Agents with the Disk Diffusion Method

PURPOSE/AIM OF THE STUDY

To identify the causative fungi of fungal keratitis, test their susceptibility to antifungal agents with the disk diffusion method and study the relationship between the organisms, the inhibition zones and the clinical outcomes.

MATERIALS AND METHODS

535 patients with fungal keratitis in one eye were included in this study. Pathogenic fungi were isolated by corneal scraping, identified by fungal cultivation and subjected to drug sensitivity tests conducted with the disk diffusion method. The patients were treated initially with voriconazole, terbinafine and natamycin eye drops for one week. Further treatment continued using the most effective drug according to the drug sensitivity results. The patients were followed up every week until three months after cured. The inhibition zones of fungi cultured with voriconazole, terbinafine and natamycin were compared. The relationship between inhibition zones and organism, organism and treatment results measure, and each treatment results measure and inhibition zones were evaluated.

RESULTS

Of 535 patients, 53.84%, 19.25% and 26.91% were infected with Aspergillus, Fusarium and other fungi, respectively. Keratitis patients infected with Aspergillus keratitis had the worst outcome. The size of the inhibition zones of Aspergillus spp., Fusarium spp. and other fungal genera differed significantly in response to voriconazole, terbinafine and natamycin. The inhibition zone associated with natamycin correlated significantly with the clinical outcome of fungal keratitis (OR = 0.925), but no other such correlations were found for the other drugs tested.

CONCLUSIONS

Aspergillus and Fusarium were the predominant pathogenic genera causing fungal keratitis in our patients. Among the causative fungi, infections due to Aspergillus spp. were associated with the worst outcomes. The inhibition zones of fungal isolates in response to natamycin significantly correlated with the treatment outcomes of keratitis. Specifically, the smaller the natamycin inhibition zone, the lower the probability that the fungal keratitis had been eliminated.

Molecular identification and antifungal susceptibility profile of Aspergillus flavus isolates recovered from clinical specimens in Kuwait

BACKGROUND

Within the genus Aspergillus, A. flavus is the second most important species of clinical significance. It is predominantly associated with infections involving sinuses, eye and skin, mostly in geographic regions with hot and arid climate, including the Middle East. Recent reports on emergence of resistance to triazoles among Aspergillus spp. is a cause of concern for treatment of patients with invasive aspergillosis. In this study we present data on genetic characterization and antifungal susceptibility profile of clinical and environmental isolates of A. flavus.

METHODS

Ninety-nine Aspergillus section Flavi isolates, originating from clinical (n=92) and environmental (n=7) sources, initially identified by morphological characteristics, were analyzed by partial sequencing of β-tubulin and calmodulin gene fragments and their susceptibilities to six antifungal agents was determined by Etest on RPMI1640 and Muller-Hinton agar media. Etest minimum inhibitory concentrations (MICs) of amphotericin B and voriconazole were also compared with zone of inhibition diameters obtained by disc diffusion test on RPMI agar medium.

RESULTS

The identity of all clinical and environmental isolates was confirmed as A. flavus species by combined analysis of β-tubulin and calmodulin genes. The mean MIC90 (μg/ml) values on RPMI medium for amphotericin B, voriconazole, posaconazole, anidulafungin, micafungin and caspofungin were 3, 0.25, 0.25, 0.002, 0.002 and 0.032, respectively. No environmental isolate exhibited MIC value of >2 μg/ml for amphotericin B. For clinical isolates, the zone of inhibition diameters for amphotericin B and voriconazole ranged from 7-16 mm and 24-34 mm, respectively. Linear regression analysis between Etest MIC values and disk diffusion diameters revealed a significant inverse correlation with amphotericin B (p <0.001) and voriconazole (p<0.003).

CONCLUSIONS

The β-tubulin and calmodulin gene sequences confirmed that all 92 clinical isolates identified phenotypically belonged to A. flavus taxon, thus suggesting that the other species within Aspergillus section Flavi are of little clinical significance. Triazoles and echinocandins showed very good in vitro activity against the A. flavus, however, 10% clinical isolates showed MICs of >2 μg/ml for amphotericin B.