Current status of antifungal susceptibility testing methods

Prolonged treatment of dermatophytosis caused by Trichophyton indotinea with terbinafine or itraconazole impacts better outcomes irrespective of mutation in the squalene epoxidase gene

BACKGROUND

Over the past decades, the increasing incidence of recurrent dermatophytosis associated with terbinafine-resistant Trichophyton has posed a serious challenge in management of dermatophytosis. Independent reports of failure of treatment and high minimum inhibitory concentrations (MIC) of antifungals are available, but data correlating MIC and clinical outcomes is still sparse. Therefore, the present study was conducted to evaluate the outcomes of systemic treatment of dermatophytosis and its correlation with MIC of the etiological agents isolated from such patients.

METHODS

Retrospective analysis of 587 consecutive patients with dermatophytosis was done from March 2017 to March 2019. Demographic and clinical details of the patients were noted, along with the results of direct microscopy and fungal culture. The isolates were identified by sequencing the internal transcribed spacer region of rDNA. Antifungal susceptibility testing was performed following the CLSI M38 protocol. Mutation in the squalene epoxidase (SE) gene was detected by DNA sequencing and ARMS-PCR. Based on the culture-positivity and prescribed systemic antifungal, patients were categorised into Group I culture-positive cases treated with systemic terbinafine and Group II culture-positive cases treated with systemic itraconazole, each for a total period of 12 weeks.

RESULTS

In the present study, 477 (81.39%) were culture-positive; however, 12 weeks follow-up was available for 294 patients (Group I-157 and Group II-137) who were included for statistical analysis. In both groups [Group I-37/63 (51.4%) and Group II-14/54 (58.3%)], a better cure rate was observed if the initiation of therapy was performed within <6 months of illness. Treatment outcome revealed that if therapy was extended for 8-12 weeks, the odds of cure rate are significantly better (p < .001) with either itraconazole (Odd Ratio-15.5) or terbinafine (Odd Ratio-4.34). Higher MICs for terbinafine were noted in 41 cases (cured-18 and uncured-23) in Group I and 39 cases (cured-16 and uncured-23) in Group II. From cured (Group I-17/18; 94.4% and Group II-14/16; 87.5%) and uncured (Group I-20/23; 86.9% and Group II-21/23; 91.3%) cases had F397L mutation in the SE gene. No significant difference in cure rate was observed in patients with Trichophyton spp. having terbinafine MIC ≥ 1or <1 μg/mL (Group I-p = .712 and Group II-p = .69).

CONCLUSION

This study revealed that prolonging terbinafine or itraconazole therapy for beyond 8 weeks rather than the standard 4 weeks significantly increases the cure rate. Moreover, no correlation has been observed between antifungal susceptibility and clinical outcomes. The MIC remains the primary parameter for defining antifungal activity and predicting the potency of antifungal agents against specific fungi. However, predicting therapeutic success based solely on the MIC of a fungal strain is not always reliable, as studies have shown a poor correlation between in vitro data and in vivo outcomes. To address this issue, further correlation of antifungal susceptibility testing (AFST) data with clinical outcomes and therapeutic drug monitoring is needed. It also highlights that initiation of the treatment within <6 months of illness increases cure rates and reduces recurrence. Extensive research is warranted to establish a better treatment regime for dermatophytosis.

Enhancing the Antifungal Efficacy of Fluconazole with a Diterpene: Abietic Acid as a Promising Adjuvant to Combat Antifungal Resistance in Candida spp

The increasing antifungal resistance rates against conventional drugs reveal the urgent need to search for new therapeutic alternatives. In this context, natural bioactive compounds have a critical role in antifungal drug development. Since evidence demonstrates that abietic acid, a diterpene found in Pinus species, has significant antimicrobial properties, this study aimed to evaluate the antifungal activity of abietic acid against Candida spp and its ability to potentiate the activity of fluconazole. Abietic acid was tested both individually and in combination with fluconazole against Candida albicans (CA INCQS 40006), Candida krusei (CK INCQS 40095), and Candida tropicalis (CT INCQS 40042). The microdilution method was used to determine the IC50 and the cell viability curve. Minimum Fungicidal Concentration (MFC) was determined by subculture in a solid medium. The plasma membrane permeability was measured using a fluorescent SYTOX Green probe. While the IC50 of the drugs alone ranged between 1065 and 3255 μg/mL, the IC50 resulting from the combination of abietic acid and fluconazole ranged between 7563 and 160.1 μg/mL. Whether used in combination with fluconazole or isolated, abietic acid exhibited Minimum Fungicidal Concentration (MFC) values exceeding 1024 μg/mL against Candida albicans, Candida krusei and Candida tropicalis. However, it was observed that the antifungal effect of fluconazole was enhanced when used in combination with abietic acid against Candida albicans and Candida tropicalis. These findings suggest that while abietic acid alone has limited inherent antifungal activity, it can enhance the effectiveness of fluconazole, thereby reducing antifungal resistance.

ERG11 Gene Variability and Azole Susceptibility in Malassezia pachydermatis

Malassezia pachydermatis is part of the normal skin microbiota of various animal species but under certain circumstances becomes an opportunistic pathogen producing otitis and dermatitis. Commonly these Malassezia diseases are effectively treated using azoles. However, some cases of treatment failure have been reported. Alterations in the ERG11 gene have been associated with in vitro azole resistance in M. pachydermatis. In the present study, in vitro antifungal susceptibility of 89 different strains of M. pachydermatis isolated from different animal species and health status was studied. The susceptibility to fluconazole (FLZ), itraconazole (ITZ), ketoconazole and amphotericin B was tested by a disk diffusion method and 17 strains were also subjected to an ITZ E-test. Mueller-Hinton supplemented with 2% glucose and methylene blue was used as culture medium in both susceptibility assays. Multilocus sequence typing was performed in 30 selected strains using D1D2, ITS, CHS2 and β-tubulin genes. Also, ERG11 gene was sequenced. The four antifungals tested were highly effective against most of the strains. Only two strains showed no inhibition zone to antifungals and a strain showed an increased MIC to ITZ. The study of the ERG11 sequences revealed a high diversity of DNA sequences and a total of 23 amino acid substitutions, from which only two have been previously described. Also, three deleterious substitutions (A302T, G459D and G461D) previously associated with azole resistance in this yeast were recovered. A correlation between certain genotypes and ERG11 mutations was observed. Some of the ERG11 mutations recovered were correlated with a reduced susceptibility to azoles.

Tinea capitis among schoolchildren in Ethiopia: A systematic review and meta analysis

BACKGROUND

Tinea capitis accounts for25 to 30% of all fungal infections, but it is often ignored because it is not life threatening in nature. It is more common among schoolchildren particularly in developing countries. Due to the presence of significant variability among the previous studies, this study was conducted to provide a pooled prevalence and associated factors of tinea capitis in Ethiopian schoolchildren.

METHOD

We conducted a systematic search in five major databases for articles similar to our topic. This review included school-based cross-sectional studies that were reported in English and conducted from 2006 through 2022. The data were extracted using Microsoft Excel and further analysis was done using StataTM Version 17.0 statistical software. Forest plots were used to assess the presence of heterogeneity with 95% confidence intervals. A random effects meta- analysis model was used to pool primary estimates. To declare the presence or absence of association, 95% confidence interval with odds ratio was used.

RESULTS

Fourteen studies with a total of 9465 schoolchildren were included. The pooled prevalence was 29.03% (95%CI: 15.37-42.71). There was observed heterogeneity, which could be explained by publication bias (P = 0.04). Family history of tinea capitis (OR: 9.18, 95%CI: 3.5-24.02), under the age of 10 years (OR: 1.65, 95%CI: 1.17-2.33) were factors increasing the development of tinea capitis among schoolchildren and schoolchildren who had hair wash at least once a week (OR: 0.31, 95%CI: 0.24-0.42) was significantly associated with reduced risk for tinea capitis.

CONCLUSION

One of the most prevalent childhood health condition in Ethiopia is tinea capitis, which affects over one in every four schoolchildren. Schoolchildren who had family history of tinea capitis and under the age of 10 years were the identified risk factors but they had hair wash at least once a week was the protective factor of tinea capitis among schoolchildren. Clinical and public engagement activities are needed to overcome the burden of the disease.

Current Landscape of Methods to Evaluate Antimicrobial Activity of Natural Extracts

Natural extracts have been and continue to be used to treat a wide range of medical conditions, from infectious diseases to cancer, based on their convenience and therapeutic potential. Natural products derived from microbes, plants, and animals offer a broad variety of molecules and chemical compounds. Natural products are not only one of the most important sources for innovative drug development for animal and human health, but they are also an inspiration for synthetic biology and chemistry scientists towards the discovery of new bioactive compounds and pharmaceuticals. This is particularly relevant in the current context, where antimicrobial resistance has risen as a global health problem. Thus, efforts are being directed toward studying natural compounds' chemical composition and bioactive potential to generate drugs with better efficacy and lower toxicity than existing molecules. Currently, a wide range of methodologies are used to analyze the in vitro activity of natural extracts to determine their suitability as antimicrobial agents. Despite traditional technologies being the most employed, technological advances have contributed to the implementation of methods able to circumvent issues related to analysis capacity, time, sensitivity, and reproducibility. This review produces an updated analysis of the conventional and current methods to evaluate the antimicrobial activity of natural compounds.

Evaluation of antifungal susceptibility and clinical characteristics in fungal keratitis in a tertiary care center in North India

Purpose

To study the antifungal susceptibility of common corneal pathogenic fungi to antifungal agents in the North Indian population.

Methods

Prospective study of the antifungal sensitivity testing (natamycin, amphotericin B, voriconazole, itraconazole, fluconazole, posaconazole, caspofungin, micafungin) of fungal isolates from 50 cases of culture positive fungal keratitis by using E test method. Details noted included demographic data, visual acuity, clinical details, grade of keratitis, healing time, and success in medical management.

Results

Of 50 patients with fungal keratitis (mean age: 40.28 ± 16.77 years), 12 eyes healed within 3 weeks, 14 had a delayed healing response, and 24 had chronic keratitis. Among the 15 cases of Fusarium isolates, 93.3% were sensitive to natamycin, while 40% to amphotericin B; 66.6% to voriconazole, 13.4% to itraconazole and fluconazole each. 80% of Fusarium cases (n = 12) showed susceptibility to posaconazole. Among Aspergillus flavus isolates, 53.4% (n = 8) were sensitive to natamycin, with only 40% (n = 7) showing sensitivity to amphotericin B and good susceptibility to azoles. MIC against susceptible Fusarium spp. for natamycin was 3-16 μg/mL, amphotericin B: 1-8 μg/mL, voriconazole: 0.5-1.5 μg/mL, itraconazole: 0.5-12 μg/mL, posaconazole: 0.094-1.5 μg/mL. MIC against Aspergillus flavus was natamycin: 8-32 μg/mL, amphotericin B: 0.5-16 μg/mL, voriconazole: 0.025-4 μg/mL, itraconazole: 0.125-8 μg/mL, posaconazole: 0.047-0.25 μg/mL; against Aspergillus niger isolates, to natamycin was 6 μg/mL (n=1), amphotericin B 8-12 μg/mL (n = 3), voriconazole: 0.125-0.19 μg/mL (n = 3), itraconazole: 0.38-0.75 μg/mL, posaconazole: 0.064-0.19 μg/mL and against Aspergillus fumigatus (n = 1), was natamycin4 μg/mL, amphotericin B - 8 μg/mL, voriconazole 0.25 μg/mL, itraconazole 1 μg/mL, and posaconazole 0.19 μg/mL. MIC against susceptible Acremonium spp. for natamycin was 1.5-16 μg/mL, amphotericin B: 0.5-8 μg/mL, voriconazole: 0.19-3 μg/mL, itraconazole: 0.125 μg/mL, posaconazole: 0.125-0.5 μg/mL and against susceptible Curvularia was natamycin 0.75-4 μg/mL, amphotericin B 0.5-1 μg/mL, voriconazole 0.125-0.19 μg/mL, itraconazole 0.047-0.094 μg/mL, posaconazole 0.047-0.094 μg/mL. MIC against Mucor spp.+ Rhizopus spp. (n = 1) was natamycin: 8 μg/mL, amphotericin B: 0.75 μg/mL, posaconazole: 1.5 μg/mL. MIC against of Alternaria (n = 1) was voriconazole: 0.19 μg/mL, posaconazole: 0.094 μg/mL. MIC against Penicillium (n=1) was natamycin: 8 μg/mL, voriconazole: 0.25 μg/mL, itraconazole: 0.5 μg/mL, and Posaconazole: 0.125 μg/mL.

Conclusion

Our observations highlight the variations in susceptibility to antifungal agents. Posaconazole seems to be effective with low MIC against common corneal pathogenic fungal isolates.

Paving the Way to Overcome Antifungal Drug Resistance: Current Practices and Novel Developments for Rapid and Reliable Antifungal Susceptibility Testing

The past year has established the link between the COVID-19 pandemic and the global spread of severe fungal infections; thus, underscoring the critical need for rapid and realizable fungal disease diagnostics. While in recent years, health authorities, such as the Centers for Disease Control and Prevention, have reported the alarming emergence and spread of drug-resistant pathogenic fungi and warned against the devastating consequences, progress in the diagnosis and treatment of fungal infections is limited. Early diagnosis and patient-tailored therapy are established to be key in reducing morbidity and mortality associated with fungal (and cofungal) infections. As such, antifungal susceptibility testing (AFST) is crucial in revealing susceptibility or resistance of these pathogens and initiating correct antifungal therapy. Today, gold standard AFST methods require several days for completion, and thus this much delayed time for answer limits their clinical application. This review focuses on the advancements made in developing novel AFST techniques and discusses their implications in the context of the practiced clinical workflow. The aim of this work is to highlight the advantages and drawbacks of currently available methods and identify the main gaps hindering their progress toward clinical application.

Antifungal activity of thiosemicarbazones, bis(thiosemicarbazones), and their metal complexes

Fungi are ubiquitous in nature, and typically cause little or no environmental or pathogenic damage to their plant, animal, and human hosts. However, a small but growing number of pathogenic fungi are spreading world-wide at an alarming rate threatening global ecosystem health and proliferation. Many of these emerging pathogens have developed multi-drug resistance to front line therapeutics increasing the urgency for the development of new antifungal agents. This review examines the development of thiosemicarbazones, bis(thiosemicarbazones), and their metal complexes as potential antifungal agents against more than 65 different fungal strains. The fungistatic activity of the compounds are quantified based on the zone of inhibition, minimum inhibitory concentration, or growth inhibition percentage. In this review, reported activities were standardized based on molar concentrations to simplify comparisons between different compounds. Of all the fungal strains reported in the review, A. niger in particular was very resistant towards a majority of tested compounds. Our analysis of the data shows that metal complexes are typically more active than non-coordinated ligands with copper(II) and zinc(II) complexes generally displaying the highest activity.

Chemical Composition and Antimicrobial Properties of Mentha × piperita cv. 'Kristinka' Essential Oil

Several economically important crops, fruits and vegetables are susceptible to infection by pathogenic fungi and/or bacteria postharvest or in field. Recently, plant essential oils (EOs) extracted from different medicinal and officinal plants have had promising antimicrobial effects against phytopathogens. In the present study, the potential microbicide activity of Mentha × piperita cv. ‘Kristinka’ (peppermint) EO and its main constituents have been evaluated against some common phytopathogens. In addition, the cell membrane permeability of the tested fungi and the minimum fungicidal concentrations were measured. The antifungal activity was tested against the following postharvest fungi: Botrytis cinerea, Monilinia fructicola, Penicillium expansum and Aspergillus niger, whereas antibacterial activity was evaluated against Clavibacter michiganensis, Xanthomonas campestris, Pseudomonas savastanoi and P. syringae pv. phaseolicola. The chemical analysis has been carried out using GC-MS and the main components were identified as menthol (70.08%) and menthone (14.49%) followed by limonene (4.32%), menthyl acetate (3.76%) and β-caryophyllene (2.96%). The results show that the tested EO has promising antifungal activity against all tested fungi, whereas they demonstrated only a moderate antibacterial effect against some of the tested bacteria.

Antifungal and anti-biofilm activity of a new Spanish extract of propolis against Candida glabrata

Background

Resistance to traditional antifungal agents is a considerable health problem nowadays, aggravated by infectious processes related to biofilm formation, usually on implantable devices. Therefore, it is necessary to identify new antimicrobial molecules, such as natural products, to develop new therapeutic strategies to prevent and eradicate these infections. One promising product is propolis, a natural resin produced by honeybees with substances from various botanical sources, beeswax and salivary enzymes. The aim of this work was to study the effect of a new Spanish ethanolic extract of propolis (SEEP) on growth, cell surface hydrophobicity, adherence and biofilm formation of Candida glabrata, a yeast capable of achieving high levels of resistance to available anti-fungal agents.

Methods

The antifungal activity of SEEP was evaluated in the planktonic cells of 12 clinical isolates of C. glabrata. The minimum inhibitory concentration (MIC) of propolis was determined by quantifying visible growth inhibition by serial plate dilutions. The minimum fungicide concentration (MFC) was evaluated as the lowest concentration of propolis that produced a 95% decrease in cfu/mL, and is presented as MFC₅₀ and MFC₉₀, which corresponds to the minimum concentrations at which 50 and 90% of the C. glabrata isolates were inhibited, respectively. Influence on cell surface hydrophobicity (CSH) was determined by the method of microbial adhesion to hydrocarbons (MATH). The propolis effect on adhesion and biofilm formation was determined in microtiter plates by measurement of optical density (OD) and metabolic activity (XTT-assay) in the presence of sub-MIC concentrations of SEEP.

Results

SEEP had antifungal capacity against C. glabrata isolates, with a MIC₅₀ of 0.2% (v/v) and an MFC₅₀ of 0.4%, even in azole-resistant strains. SEEP did not have a clear effect on surface hydrophobicity and adhesion, but an inhibitory effect on biofilm formation was observed at subinhibitory concentrations (0.1 and 0.05%) with a significant decrease in biofilm metabolism.

Conclusions

The novel Spanish ethanolic extract of propolis shows antifungal activity against C. glabrata, and decreases biofilm formation. These results suggest its possible use in the control of fungal infections associated with biofilms.

Biochar as a Biocompatible Mild Anti-Inflammatory Supplement for Animal Feed and Agricultural Fields

Biochar is an organic material and high in carbon content, besides its use for energy purposes, it is also a material that serves the purpose of improving soil fertility, organic matter content of soils and removing heavy metals from water and soil. This study aims to investigate the antimicrobial effects of biochar whose beneficial effects on agricultural productivity has been proven by different studies. Scientific literature concerning the antibacterial, antifungal, and antiviral effects of the apricot seed and olive seed biochar is limited. Biochar applications may help to alter the microbial diversity by modifying biological environment either in agriculture or in animal husbandry. Moreover, biochar has been used in animal husbandry to improve animal health especially by regulating the intestinal flora and inflammation in the intestines. Hence, in our study, we investigated the effect of biochar on the growth of Aspergillus niger, Cryphonectria parasitica, Phytophthora cinnamomi, Plenodomus tracheiphilus, Enterococcus casseliflavus, Staphylococcus aureus, Pseudomonas aeruginosa, Escherichia coli and two different bacteriophage strains. Biochar did not have any direct effect on the growth of either Gram-positive or Gram-negative bacteria, bacteriophages, and fungi. In order to test their direct effects on the immune cells, mammalian macrophages were used and biochar directly reduced the inflammatory cytokine levels produced by the in vitro activated macrophages.

Change in species distribution and antifungal susceptibility of candidemias in an intensive care unit of a university hospital (10-year experience)

Candidemia is a nosocomial infection mostly found in critically ill patients. Our objectives were to evaluate the change in distribution and resistance profile of Candida spp. isolated from candidemic patients in our intensive care unit over two 5-year periods spanning 15 years and to evaluate the risk factors. Records from the microbiology laboratory were obtained, from January 2004 to December 2008 and from January 2013 to December 2017, retrospectively. Antifungal susceptibility was performed by E-test and evaluated according to EUCAST breakpoints. A total of 210 candidemia cases occurred; 238 Candida spp. were isolated in 197 patients (58.8% male; mean age, 59.2 ± 19.6 years). The most predominant risk factor was central venous catheter use. Species distribution rates were 32%, 28%, 17%, and 11% for C. albicans (n = 76), C. parapsilosis (n = 67), C. glabrata (n = 40), and C. tropicalis (n = 27), respectively. Resistance rate to anidulafungin was high in C. parapsilosis over both periods and increased to 73% in the second period. Fluconazole showed a remarkable decrease for susceptibility in C. parapsilosis (94 to 49%). The prevalence of MDR C. parapsilosis (6%/33%) and C. glabrata (0%/44%) increased in the second period. We observed a predominance of non-albicans Candida spp., with C. parapsilosis being the most frequent and C. glabrata infections presenting with the highest mortality. High level of echinocandin resistance in C. parapsilosis and increasing prevalences of MDR C. parapsilosis and C. glabrata seem emerging challenges in our institution.

Recent advances on mycotic keratitis caused by dematiaceous hyphomycetes

Dematiaceous hyphomycetes (DH) are darkly pigmented fungi ubiquitously found all over the world as plant pathogens and saprophytes, and many of the members of this group have emerged as opportunistic pathogens. These fungi are responsible for a wide variety of infections including mycotic keratitis, which is considered as one of the major causes of corneal blindness, particularly in tropical and subtropical countries with an annual global burden of about 1 000 000 patients. The infection is more common in workers working in an outdoor environment. Moreover, trauma is found to be the most important predisposing cause of mycotic keratitis. Considerable delay in diagnosis and scarcity of effective pharmacological drugs are the major factors responsible for increased morbidity and visual impairment. Considering the crucial role of DH in mycotic keratitis, in the present review, we have focused on major DH with special emphasis on their pathogenicity, diagnosis and treatment strategies.

Antifungal and antibiofilm activities of the essential oil of leaves from Lippia gracilis Schauer against phytopathogenic fungi

AIMS

This study aimed to evaluate the antifungal and antibiofilm effects of essential oil (EO) from leaves of Lippia gracilis and its major constituents, thymol and carvacrol, against phytopathogenic fungi.

METHODS AND RESULTS

The leaves of L. gracilis were hydrodistilled to obtain the EO and the chemical composition was determined by GC/MS analysis. The antifungal activity of EO of L. gracilis was evaluated on the vegetative and mycelial growth of Colletotrichum gloeosporioides, Colletotrichum lindemuthianum, Fusarium oxysporum and Fusarium solani. In addition, the ability of the oil to inhibit fungal biofilm formation was assessed by total biomass quantification using crystal violet staining, analysis of metabolic activity, and scanning electron microscopy (SEM). Moreover the antifungal and antibiofilm activities of the monoterpenes, thymol and carvacrol, present in EO of L. gracilis were evaluated against F. oxysporum. The analysis of the chemical composition of EO extracted from L. gracilis, revealed the presence of monoterpenes (94·13%), which included carvacrol (48·57%) and thymol (7·78%), and 4 sesquiterpenes (3·74%). In general, EO showed significant antifungal activity and inhibited the formation of fungal biofilms. Furthermore, thymol and carvacrol showed significant antifungal and antibiofilm activities against F. oxysporum. SEM images showed structural changes in fungal morphology upon treatment with EO of L. gracilis.

CONCLUSION

The results presented in this study showed promising antifungal and antibiofilm effects of EO of L. gracilis and its major components, carvacrol and thymol.

SIGNIFICANCE AND IMPACT OF THE STUDY

These findings indicate that the EO extracted from L. gracilis, and the monoterpenes, carvacrol and thymol have a great potential as antifungal and antibiofilm agents. Furthermore, this is the first report of the antibiofilm activity of the EO of L. gracilis and its major components against phytopathogenic fungi.

Factors influencing susceptibility testing of antifungal drugs: a critical review of document M27-A4 from the Clinical and Laboratory Standards Institute (CLSI)

Due to the increasing numbers of fungal infections and the emergence of drug-resistant fungi, optimization and standardization of diagnostic methods for the measurement of antifungal susceptibility are ongoing. The M27-A4 document by the US Clinical and Laboratory Standards Institute (CLSI) is presently used for the interpretation of minimum inhibitory concentrations of major opportunistic yeast species as measured by broth microdilution testing in many countries. Although microdilution is considered a benchmark for reproducible and accurate results, increased testing capacity, and limited human bias, the method is often inaccessible to routine clinical laboratories and researchers, especially in low-income countries. Furthermore, several studies suggest that there are still a considerable number of factors that make the estimation of in vitro activity of antifungal agents challenging. This review article summarizes the limitations of the M27-A4 standard which, despite the advances and improvements obtained by the standardization of antimicrobial resistance testing methods by CLSI, still persist.

A Collaborative Tale of Diagnosing and Treating Chronic Pulmonary Aspergillosis, from the Perspectives of Clinical Microbiologists, Surgical Pathologists, and Infectious Disease Clinicians

Chronic pulmonary aspergillosis (CPA) refers to a spectrum of Aspergillus-mediated disease that is associated with high morbidity and mortality, with its true prevalence vastly underestimated. The diagnosis of CPA includes characteristic radiographical findings in conjunction with persistent and systemic symptoms present for at least three months, and evidence of Aspergillus infection. Traditionally, Aspergillus infection has been confirmed through histopathology and microbiological studies, including fungal culture and serology, but these methodologies have limitations that are discussed in this review. The treatment of CPA requires an individualized approach and consideration of both medical and surgical options. Most Aspergillus species are considered susceptible to mold-active triazoles, echinocandins, and amphotericin B; however, antifungal resistance is emerging and well documented, demonstrating the need for novel therapies and antifungal susceptibility testing that correlates with clinical response. Here, we describe the clinical presentation, diagnosis, and treatment of CPA, with an emphasis on the strengths and pitfalls of diagnostic and treatment approaches, as well as future directions, including whole genome sequencing and metagenomic sequencing. The advancement of molecular technology enables rapid and precise species level identification, and the determination of molecular mechanisms of resistance, bridging the clinical infectious disease, anatomical pathology, microbiology, and molecular biology disciplines.

Antifungal Resistance Regarding Malassezia pachydermatis: Where Are We Now?

Malassezia pachydermatis is a yeast inhabiting the skin and ear canals in healthy dogs. In the presence of various predisposing conditions it can cause otitis and dermatitis, which are treated with multiple antifungal agents, mainly azole derivatives. This manuscript aims to review the available evidence regarding the occurrence of resistance phenomena in this organism. Various findings support the capacity of M. pachydermatis for developing resistance. These include some reports of treatment failure in dogs, the reduced antifungal activity found against yeast isolates sampled from dogs with exposure to antifungal drugs and strains exposed to antifungal agents in vitro, and the description of resistance mechanisms. At the same time, the data reviewed may suggest that the development of resistance is a rare eventuality in canine practice. For example, only three publications describe confirmed cases of treatment failure due to antifungal resistance, and most claims of resistance made by past studies are based on interpretive breakpoints that lack sound support from the clinical perspective. However, it is possible that resistant cases are underreported in literature, perhaps due to the difficulty of obtaining a laboratory confirmation given that a standard procedure for susceptibility testing of M. pachydermatis is still unavailable. These considerations highlight the need for maintaining surveillance for the possible emergence of clinically relevant resistance, hopefully through a shared strategy put in place by the scientific community.

Identification and Testing of Antidermatophytic Oxaborole-6-Benzene Sulphonamide Derivative (OXBS) from Streptomyces atrovirens KM192347 Isolated from Soil

There is a need to continue research to find out other anti-dermatophytic agents to inhibit causal pathogenic skin diseases including many types of tinea. We undertook the production, purification, and identification of an anti-dermatophytic substance by Streptomyces atrovirens. Out of 103 streptomycete isolates tested, only 20 of them showed antidermatophytic activity with variable degrees against Trichophyton tonsurans CCASU 56400 (T. tonsurans), Microsporum canis CCASU 56402 (M. canis), and Trichophyton mentagrophytes CCASU 56404 (T. mentagrophytes). The most potent isolate, S₁₀Q₆, was identified based on the tests conducted that identified morphological and physiological characteristics and using 16S rRNA gene sequencing. The isolate was found to be closely correlated to previously described species Streptomyces atrovirens; it was designated Streptomyces atrovirens KM192347 (S. atrovirens). Maximum antifungal activity of the strain KM192347 was obtained in modified starch nitrate medium (MSNM) adjusted initially at pH 7.0 and incubated at 30 °C in shaken cultures (150 rpm) for seven days. The antifungal compound was purified by using two steps protocol including solvent extraction and column chromatography. The MIC of it was 20 µg/mL against the dermatophyte cultures tested. According to the data obtained from instrumental analysis and surveying the novel antibiotics database, the antidermatophytic substance produced by the strain KM192347 was characterized as an oxaborole-6-benzene sulphonamide derivative and designated oxaborole-6-benzene sulphonamide (OXBS) with the chemical formula C₁₃H₁₂ BNO₄S. The crude OXBS didn’t show any toxicity on living cells. Finally, the results obtained herein described another anti-dermatophytic substance named an OXBS derivative.

Azole resistance of Malassezia pachydermatis causing treatment failure in a dog

A 5-year-old neutered female toy Poodle chronically treated with systemic and topical azoles to control recurrent Malassezia dermatitis/otitis was presented because of the loss of treatment efficacy. Minimum Inhibitory Concentrations (MICs) obtained in vitro for various azoles (especially itraconazole and ketoconazole) against Malassezia strains isolated from the dog were increased by several-fold compared with MICs obtained for control isolates. These results reinforced the assumption based on clinical observation, i.e. the development of azole resistance

Green multicomponent synthesis, antimicrobial and antioxidant evaluation of novel 5-amino-isoxazole-4-carbonitriles

Background

Design and synthesis of new inhibitor agents to deal with pathogenic microorganisms is expanding. In this project, an efficient, environmentally friendly, economical, rapid and mild procedure was developed for the synthesis of novel functionalized isoxazole derivatives as antimicrobial potentials.

Methods

Multicomponent reaction between malononitrile (1), hydroxylamine hydrochloride (2) and different aryl or heteroaryl aldehydes 3a–i afforded novel 5-amino-isoxazole-4-carbonitriles 4a–i in good product yields and short reaction times. Deep eutectic solvent K₂CO₃/glycerol was used as catalytic reaction media. Structure of all molecules were characterized by different analytical tools. In vitro inhibitory activity of all derivatives was evaluated against a variety of pathogenic bacteria including both Gram-negative and Gram-positive strains as well as some fungi. In addition, their free radical scavenging activities were assessed against DPPH.

Results

Broad-spectrum antimicrobial activities were observed with isoxazoles 4a, b, d. In addition, antioxidant activity of isoxazole 4i was proven on DPPH.

Conclusions

In this project, compounds 4a, b, d could efficiently inhibit the growth of various bacterial and fungal pathogens. Antioxidant properties of derivative 4i were also significant. These biologically active compounds are suitable candidates to synthesize new prodrugs and drugs due to the presence of different functional groups on their rings.

Electronic supplementary material

The online version of this article (10.1186/s13065-018-0488-0) contains supplementary material, which is available to authorized users.

Antimicrobial Activity of NCR Plant Peptides Strongly Depends on the Test Assays

The symbiosis specific NCR247 and NCR335 cationic plant peptides of Medicago truncatula have been shown to exert antimicrobial activity against a wide range of microbes. However, their antimicrobial efficiency is clearly limited by divalent cations. Here, the antibacterial and antifungal activities of NCR247 and NCR335 peptides were compared to those of the well-characterized peptide antibiotics polymyxin B and the aminoglycoside streptomycin on three model microbes, Escherichia coli, Bacillus subtilis and Saccharomyces cerevisiae as representatives of Gram-negative and Gram-positive bacteria as well as eukaryotic fungi. The aim of the study was to assess how the killing efficiency of these peptides depends on various, widely used antimicrobial susceptibility assays. Validated resazurin microdilution assay was used to determine minimal growth inhibitory concentrations in three general test media (MHB, MHBII and low-salt medium LSM). Bactericidal/fungicidal activities were determined by the commonly used drop plate assay. The natural plant peptides showed distinct characteristics, NCR247 had a generally high sensitivity for Ca²⁺ and Mg²⁺ in the medium, while NCR335 proved to be a robust and strong antimicrobial agent with comparable efficiency values to polymyxin B. Activity data were confirmed visually, both NCR247 and NCR335 treatments at minimal bactericidal concentrations induced complete disruption of the membranes and provoked cell lysis on all tested microorganisms as observed by scanning electron microscopy.

Expedient multicomponent synthesis of a small library of some novel highly substituted pyrido[2,3-d]pyrimidine derivatives mediated and promoted by deep eutectic solvent and in vitro and quantum mechanical study of their antibacterial and antifungal activities

A facile and efficient catalyst- and oxidant-free multicomponent synthesis of a small library of highly substituted pyrido[2,3-d]pyrimidine derivatives is reported. The products were obtained within relatively short reaction times in good to excellent yields in the presence of deep eutectic solvents as media and promoters. Simple purification and reusability of the deep eutectic solvent were the other beneficial factors of the reported protocol. All of the synthesized derivatives were thoroughly screened for possible in vitro antibacterial and antifungal effects against twenty-two bacterial and three fungal pathogens. Some of the prepared pyrido[2,3-d]pyrimidine derivatives showed remarkable antibacterial and antifungal activities in comparison with some typical known antibacterial and antifungal agents. Finally, the derivatives possessing bioactivity effects were subjected to quantum chemical computational studies in order to reveal the probable structural and electronic effects governing the spotted bioactivities. It was found that the observed bioactivities could be best devoted to the HOMO-LUMO energy gap and para delocalization index of the corresponding derivatives.

Antimicrobial Susceptibility of Tinea Capitis in Children from Egypt

Background

Dermatophytic fungi of genera Trichophyton and Microsporum are the most important fungal species causing tinea capitis. Choice of treatment for tinea capitis is determined by the species of fungus.

Aim

The aim of the study was to investigate the most prevalent fungal species causing tinea capitis in children from Egypt and the most useful antifungal agent for treatment.

Patients and Methods

A total of 100 patients diagnosed clinically with tinea capitis were included in the study. Samples were collected and sent to the microbiology and immunology laboratory for sample processing and fungal identification by routine laboratory techniques. A study of antifungal susceptibility to chosen antifungal medications (fluconazole, ketoconazole, clotrimazole, miconazole, amphotericin, caspofungin, itraconazole, terbinafine, and griseofulvin) was done by minimum inhibitory concentration technique.

Results

Our analysis revealed that Microsporum canis is the most commonly isolated strain. Amphotericin was the most effective antifungal agent followed by terbinafine. The most sensitive strain to fluconazole and griseofulvin is Microsporum gypseum, while Microsporum audouinii was mostly responsive to terbinafine.

Conclusion

Identification and evaluation of the antifungal susceptibility of the pathogenic species in a certain geographic region is important to achieve a good clinical response.

Methodological Issues in Antifungal Susceptibility Testing of Malassezia pachydermatis

Reference methods for antifungal susceptibility testing of yeasts have been developed by the Clinical and Laboratory Standards Institute (CLSI) and the European Committee on Antibiotic Susceptibility Testing (EUCAST). These methods are intended to test the main pathogenic yeasts that cause invasive infections, namely Candida spp. and Cryptococcusneoformans, while testing other yeast species introduces several additional problems in standardization not addressed by these reference procedures. As a consequence, a number of procedures have been employed in the literature to test the antifungal susceptibility of Malassezia pachydermatis. This has resulted in conflicting results. The aim of the present study is to review the procedures and the technical parameters (growth media, inoculum preparation, temperature and length of incubation, method of reading) employed for susceptibility testing of M. pachydermatis, and when possible, to propose recommendations for or against their use. Such information may be useful for the future development of a reference assay.

Antifungal Susceptibility Testing of Fusarium: A Practical Approach

In vitro susceptibility testing of Fusarium is becoming increasingly important because of frequency and diversity of infections and because resistance profiles are species-specific. Reference methods for antifungal susceptibility testing (AFST) are those of Clinical and Laboratory Standards Institute (CLSI) and European Committee on Antimicrobial Susceptibility (EUCAST), but breakpoints (BPs) have not yet been established. One of the problems is that phylogenetic distances between Fusarium species are much smaller than between species of, e.g., Candida. Epidemiological cutoff values (ECVs) for some Fusarium species have been determined in order to differentiate wild-type from non-wild-type isolates. In clinical routine, commercially available assays such as Etest, Sensititre or others provide essential agreement with reference methods. Our objective is to summarize antifungal susceptibility testing of Fusarium genus in the clinical laboratory: how to do it, when to do it, and how to interpret it.

Novel properties of Hippophae rhamnoides L. twig and leaf extracts - anti-virulence action and synergy with antifungals studied in vitro on Candida spp. model

Original, chemically characterized Sea buckthorn (SBT) twig and leaf extracts were in vitro studied in terms of anti-Candida activity. Minimum inhibitory concentrations (MICs) of the extracts against C. albicans ATCC 10231 ranged: 250 μg/ml (twig), 31.5 μg/ml (leaf), and against C. glabrata G1 (clinical isolate) - 15.6 μg/ml (twig), 3.9 μg/ml (leaf). Next the extracts have been used at their subMIC. Both extracts significantly enhanced activity of fluconazole (FLC) and caspofungin (CAS) against C. albicans and increased their efficacy against C. glabrata, measured by an agar dilution assay combined with the E-test. The extracts inhibited C. albicans morphogenesis such as germ tube and hyphae formation as well as invasion to the "Spider" Agar. Antiadhesive and anti-biofilm activities of the extracts were evaluated by Alamar Blue reduction assay. It showed not significant reduction in the degree of cell adhesion (by 10-15%) but noticeable decrease of biofilm formation (by 80% in the case of SBT-twig extract). In conclusion, this study provided the evidence that SBT extracts, used at non-cytotoxic concentrations for the fibroblasts (IC₅₀ from 664.8 μg/ml to 1060.4 μg/ml), targeted some of Candida spp. virulence factors essential for the establishment of the infection. SBT twigs, previously regarded as waste material, were shown to be also a valuable source of the substances with promising antimicrobial activity.

Fast and Accurate Microplate Method (Biolog MT2) for Detection of Fusarium Fungicides Resistance/Sensitivity

The need for finding fungicides against Fusarium is a key step in the chemical plant protection and using appropriate chemical agents. Existing, conventional methods of evaluation of Fusarium isolates resistance to fungicides are costly, time-consuming and potentially environmentally harmful due to usage of high amounts of potentially toxic chemicals. Therefore, the development of fast, accurate and effective detection methods for Fusarium resistance to fungicides is urgently required. MT2 microplates (Biolog(TM)) method is traditionally used for bacteria identification and the evaluation of their ability to utilize different carbon substrates. However, to the best of our knowledge, there is no reports concerning the use of this technical tool to determine fungicides resistance of the Fusarium isolates. For this reason, the objectives of this study are to develop a fast method for Fusarium resistance to fungicides detection and to validate the effectiveness approach between both traditional hole-plate and MT2 microplates assays. In presented study MT2 microplate-based assay was evaluated for potential use as an alternative resistance detection method. This was carried out using three commercially available fungicides, containing following active substances: triazoles (tebuconazole), benzimidazoles (carbendazim) and strobilurins (azoxystrobin), in six concentrations (0, 0.0005, 0.005, 0.05, 0.1, 0.2%), for nine selected Fusarium isolates. In this study, the particular concentrations of each fungicides was loaded into MT2 microplate wells. The wells were inoculated with the Fusarium mycelium suspended in PM4-IF inoculating fluid. Before inoculation the suspension was standardized for each isolates into 75% of transmittance. Traditional hole-plate method was used as a control assay. The fungicides concentrations in control method were the following: 0, 0.0005, 0.005, 0.05, 0.5, 1, 2, 5, 10, 25, and 50%. Strong relationships between MT2 microplate and traditional hole-plate methods were observed regarding to the detection of Fusarium resistance to various fungicides and their concentrations. The tebuconazole was most potent, providing increased efficiency in the growth inhibition of all tested isolates. Almost all among tested isolates were resistant to azoxystrobin-based fungicide. Overall, the MT2 microplates method was effective and timesaving, alternative method for determining Fusarium resistance/sensitivity to fungicides, compering to traditional hole-plate approach.

Methods for in vitro evaluating antimicrobial activity: A review

In recent years, there has been a growing interest in researching and developing new antimicrobial agents from various sources to combat microbial resistance. Therefore, a greater attention has been paid to antimicrobial activity screening and evaluating methods. Several bioassays such as disk-diffusion, well diffusion and broth or agar dilution are well known and commonly used, but others such as flow cytofluorometric and bioluminescent methods are not widely used because they require specified equipment and further evaluation for reproducibility and standardization, even if they can provide rapid results of the antimicrobial agent's effects and a better understanding of their impact on the viability and cell damage inflicted to the tested microorganism. In this review article, an exhaustive list of in vitro antimicrobial susceptibility testing methods and detailed information on their advantages and limitations are reported.

Antifungal Susceptibility Testing with Etest for Candida Species Isolated from Patients with Oral Candidiasis

Background

The necessity of performing antifungal susceptibility tests is recently increasing because of frequent cases of oral candidiasis caused by antifungal-resistant Candida species. The Etest (BioMerieux, Marcy l'Etoile, France) is a rapid and easy-to-perform in vitro antifungal susceptibility test.

Objective

The purpose of this study was to determine the minimal inhibitory concentrations (MICs) of antifungal agents by using the Etest for Candida species isolated from patients with oral candidiasis.

Methods

Forty-seven clinical isolates of Candida species (39 isolates of Candida albicans, 5 isolates of C. glabrata, and 3 isolates of C. tropicalis) were tested along with a reference strain (C. albicans ATCC 90028). The MIC end points of the Etest for fluconazole, itraconazole, voriconazole, and amphotericin B susceptibility were read after the 24-hour incubation of each isolate on RPMI 1640 agar.

Results

All Candida isolates were found susceptible to voriconazole and amphotericin B. However, all five isolates of C. glabrata were resistant to itraconazole, among which two isolates were also resistant to fluconazole.

Conclusion

This study revealed that the Etest represented a simple and efficacious method for antifungal susceptibility testing of Candida species isolated from oral candidiasis patients. Therefore, voriconazole and amphotericin B should be recommended as effective alternatives for the treatment of oral candidiasis.

Mediated bioelectrochemical system for biosensing the cell viability of Staphylococcus aureus

Staphylococcus aureus is one of the most dangerous human pathogens and is the cause of numerous illnesses ranging from moderate skin infections to life-threatening diseases. Despite advances made in identifying microorganisms, rapid detection methods for the viability of bacteria are still missing. Here, we report a rapid electrochemical assay for cell viability combining the use of double redox mediators and multiwall carbon nanotubes-screen printed electrodes (MWCNTs-SPE), ferricyanide (FCN) and 2,6-dichlorophenolindophenol (DCIP), which served as electron shuttle to enable the bacterial-electrode communications. The current originating from the metabolically active cells was recorded for probing the activity of the intracellular redox centers. Blocking of the respiratory chain pathways with electron transfer inhibitors demonstrated the involvement of the electron transport chain in the reaction. A good correlation between the number of the metabolically active cells and the current was obtained. The proposed assay has been exploited for monitoring cell proliferation of S. aureus during the growth. The sensitivity of the detection method reached 0.1 OD600. Therefore, the technique described is promising for estimating the cell number, measuring the cell viability, and probing intracellular redox center(s).

Agar Diffusion Procedures for Susceptibility Testing of Malassezia pachydermatis: Evaluation of Mueller-Hinton Agar Plus 2 % Glucose and 0.5 µg/ml Methylene Blue as the Test Medium

Aim of this study was to verify whether Mueller-Hinton agar supplemented with 2 % glucose and methylene blue (MH-GM), which is used for disk diffusion susceptibility testing of Candida species by the Clinical and Laboratory Standards Institute, is suitable for testing Malassezia pachydermatis. A variant of the disk diffusion procedure utilizing a 9-mm tablet was used to test 31 isolates against clotrimazole and miconazole using MH-GM as test medium. The MH-GM agar optimally supported the growth of all M. pachydermatis isolates, provided that the yeast inoculum was prepared with a lipid source (Tween 40 and 80). Zone edges were frequently definite and clear, facilitating the measurement of zone size and minimizing subjectivity. The inhibition zones correlated with MIC values obtained in a broth dilution assay. The agar diffusion method with MH-GM as the test medium appears as a suitable procedure for testing the susceptibility of M. pachydermatis to CTZ and MCZ in clinical laboratories. This test format may allow processing a large number of isolates in epidemiological studies. This may in turn facilitate clarifying to what extent the problem "drug resistance" accounts for cases of treatment failure in dogs with Malassezia otitis and dermatitis.

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.

Antifungal susceptibility testing: current role from the clinical laboratory perspective

Despite availability of many antifungal agents, antifungal clinical resistance occurs, perhaps as a consequence of an infecting organism found to be resistant in vitro to one or more antifungals tested. From what derives the important current role of the in vitro antifungal susceptibility testing (AFST), that is to determine which agents are like to be scarcely effective for a given infection. Thus, AFST results, if timely generated by the clinical microbiology laboratory and communicated to clinicians, can aid them in the therapeutic decision making, especially for difficult-to-treat invasive candidiasis and aspergillosis. Although recently refined AFST methods are commercially available for allowing a close antifungal resistance surveillance in many clinical setting, novel assays such as flow cytometry or MALDI-TOF mass spectrometry are upcoming tools for AFST. Based on short-time antifungal drug exposure of fungal isolates, these assays could provide a reliable means for quicker and sensitive assessment of AFST.

Rapid antifungal susceptibility testing by matrix-assisted laser desorption ionization-time of flight mass spectrometry analysis

The widespread use of antifungal agents, which is likely to expand with their enhanced availability, has promoted the emergence of drug-resistant strains. Antifungal susceptibility testing (AFST) is now an essential procedure for guiding appropriate antifungal therapy. Recently, we developed a matrix-assisted laser desorption ionization-time of flight mass spectrometry (MALDI-TOF MS)-based method that enables the detection of fungal isolates with reduced echinocandin susceptibility, relying on the proteome changes that are detectable after a 15-h exposure of fungal cells to serial drug concentrations. Here, we describe a simplified version of this approach that facilitates discrimination of the susceptible and resistant isolates of Candida albicans after a 3-h incubation in the presence of "breakpoint" level drug concentrations of the echinocandin caspofungin (CSF). Spectra at concentrations of 0 (null), 0.03 (intermediate), and 32 (maximal) μg/ml of CSF were used to create individual composite correlation index (CCI) matrices for 65 C. albicans isolates, including 13 fks1 mutants. Isolates are then classified as susceptible or resistant to CSF if the CCI values of spectra at 0.03 and 32 μg/ml are higher or lower, respectively, than the CCI values of spectra at 0.03 and 0 μg/ml. In this way, the drug resistance of C. albicans isolates to echinocandin antifungals can be quickly assessed. Furthermore, the isolate categorizations determined using MALDI-TOF MS-based AFST (ms-AFST) were consistent with the wild-type and mutant FKS1 genotypes and the AFST reference methodology. The ms-AFST approach may provide a rapid and reliable means of detecting emerging antifungal resistance and accelerating the initiation of appropriate antifungal treatment.

Increase in resistance to fluconazole and itraconazole in Trichophyton rubrum clinical isolates by sequential passages in vitro under drug pressure

Trichophyton rubrum, an anthropophilic dermatophyte fungus, is the predominant causative agent of superficial skin infections in human population. There are only scanty reports on drug susceptibility profiling of T. rubrum. Neither mechanisms for drug resistance development nor correlation between in vitro drug susceptibility and in vivo response to treatment is known for that species. In this study, changes in the in vitro susceptibilities to fluconazole (FLZ) and itraconazole (ITZ) among thirty T. rubrum clinical strains subjected to sequential passages in the presence or absence of the azoles were investigated. Each strain was passaged 12 times at 4-week intervals as three parallel cultures, maintained on a drug-free medium (1), and a medium containing FLZ (2) or ITZ (3) at subinhibitory concentrations. Susceptibility to FLZ and ITZ of the original strain and its 3 subcultures was determined by microdilution method. The MIC values of the two azoles remained unaltered for all T. rubrum strains tested, after 12 passages on a drug-free medium. Among the strains grown with FLZ, an increase in the MICs of FLZ and ITZ was noted in 17 (56.7 %) and 19 (63.3 %) strains, respectively. Increased MICs of ITZ and FLZ were demonstrated for 24 (80 %) and 20 (66.7 %) strains that were propagated with ITZ. The results indicate the capacity of T. rubrum to develop resistance toward the azoles after prolonged exposure to these drugs. Resistance of T. rubrum to azoles plays an important role in therapy failures and consequently contributes to persistence and chronicity of the infections.

Overview of invasive fungal infections

The incidence of invasive fungal infections (IFIs) has seen a marked increase in the last two decades. This is especially evident among transplant recipients, patients suffering from AIDS, in addition to those in receipt of immunosuppressive therapy. Worryingly, this increased incidence includes infections caused by opportunistic fungi and emerging fungal infections which are resistant to or certainly less susceptible than others to standard antifungal agents. As a direct response to this phenomenon, there has been a resolute effort over the past several decades to improve early and accurate diagnosis and provide reliable screening protocols thereby promoting the administration of appropriate antifungal therapy for fungal infections. Early diagnosis and treatment with antifungal therapy are vital if a patient is to survive an IFI. Substantial advancements have been made with regard to both the diagnosis and subsequent treatment of an IFI. In parallel, stark changes in the epidemiological profile of these IFIs have similarly occurred, often in direct response the type of antifungal agent being administered. The effects of an IFI can be far reaching, ranging from increased morbidity and mortality to increased length hospital stays and economic burden.

Interlaboratory reproducibility of Etest amphotericin B and caspofungin yeast susceptibility testing and comparison with the CLSI method

This study aimed to assess the interlaboratory reproducibility at four university hospital laboratories in the southeast region of France of the Etest technique for the determination of caspofungin (CAS) and amphotericin B (AMB) MICs and to compare it to the CLSI broth microdilution reference method. Consecutive clinical yeast isolates (n = 198) were included in the study. AMB and CAS MICs were read at 24 and 48 h. Interlaboratory reproducibility was estimated by using (i) an intraclass correlation coefficient (ICC), (ii) essential agreement (EA), and (iii) categorical agreement (CA). For Etest interlaboratory reproducibility for CAS, ICCs were 0.80 (95% confidence interval [CI], 0.76 to 0.84) and 0.81 (95% CI, 0.77 to 0.85) at 24 and 48 h, respectively. For AMB, the ICCs were 0.51 (95% CI, 0.43 to 0.58) and 0.69 (95% CI, 0.63 to 0.74) at 24 and 48 h, respectively. At 48 h, the between-center EAs ranged from 94.4 to 99.0% for both antifungals. For the comparison of the CLSI method and the Etest, the between-technique ICCs were 0.69 (95% CI, 0.63 to 0.74) and 0.62 (95% CI, 0.55 to 0.68) for CAS and AMB, respectively. The EAs ranged from 76.5 to 98.5% for CAS and from 90.3 to 97.4% for AMB according to the centers. CAs ranged from 87.9% to 91.4%, with four very major errors for 2 strains (1 Candida albicans strain and 1 Candida krusei strain), for CAS and from 97.5 to 99.5%, with four major errors, for AMB. In conclusion, the Etest showed a good interlaboratory reproducibility and a good correlation with the CLSI technique. It is well suited for the routine clinical laboratory and can thus be used to monitor clinical yeast isolates' in vitro susceptibilities in this setting.

Detection of amphotericin B resistance in Candida haemulonii and closely related species by use of the Etest, Vitek-2 yeast susceptibility system, and CLSI and EUCAST broth microdilution methods

The emerging fungal pathogens Candida haemulonii and Candida pseudohaemulonii often show high-level resistance to amphotericin B (AMB). We compared the utilities of five antifungal susceptibility testing methods, i.e., the Etest using Mueller-Hinton agar supplemented with glucose and methylene blue (Etest-MH), the Etest using RPMI agar supplemented with glucose (Etest-RPG), the Vitek-2 yeast susceptibility system, and the Clinical and Laboratory Standards Institute (CLSI) and European Committee on Antimicrobial Susceptibility Testing (EUCAST) broth microdilution methods, for the detection of AMB-resistant isolates of C. haemulonii and closely related species. Thirty-eight clinical isolates (8 C. haemulonii, 10 C. pseudohaemulonii, and 20 Candida auris isolates) were analyzed. Of the 18 C. haemulonii and C. pseudohaemulonii isolates, 18, 15, 18, 10, and 9 exhibited AMB MICs of >1 μg/ml by the Etest-MH, Etest-RPG, Vitek-2, CLSI, and EUCAST methods, respectively. All 20 C. auris isolates showed AMB MICs of ≤1 μg/ml by all five methods. Of the methods, the Etest-MH generated the broadest distribution of AMB MICs for all 38 isolates and showed the best discrimination between the C. haemulonii and C. pseudohaemulonii isolates (4 to 32 μg/ml) and those of C. auris (0.125 to 0.5 μg/ml). Taking the Etest-MH as the reference method, the essential agreements (within two dilutions) for the Etest-RPG, Vitek-2, CLSI, and EUCAST methods were 84, 92, 55, and 55%, respectively; the categorical agreements were 92, 92, 79, and 76%, respectively. This study provides the first data on the efficacy of the Etest-MH and its excellent agreement with Vitek-2 for discriminating AMB-resistant from AMB-susceptible isolates of these Candida species.

Evaluation of the antifungal susceptibility of Malassezia pachydermatis to clotrimazole, miconazole and thiabendazole using a modified CLSI M27-A3 microdilution method

BACKGROUND

In this study, we evaluated the antifungal susceptibility of Malassezia pachydermatis to clotrimazole (CTZ), miconazole (MCZ), and thiabendazole (TBD), azole derivatives employed in aural formulations labeled for treatment of canine otitis.

METHODS

The procedure for in vitro testing was based on the indications of the Clinical and Laboratory Standards Institute (CLSI) M27-A3 microdilution method. A lipid-enriched medium was employed to enhance the yeast growth (Christensen's urea broth, with 0.1% Tween 80 and 0.5% Tween 40 as the lipid sources), while the inoculums size corresponded to approximately 1-5 × 10(5) yeast cells/mL. Microplates were incubated at 37°C and read 48 h after inoculation. Azole MICs inhibiting fungal growth were the lowest drug concentrations that showed an optical density of ≤ 50% of the (drug-free) growth control, as assessed by spectrophotometer (630 nm filter).

RESULTS

All isolates were inhibited by the three azoles, with different minimum inhibitory concentration (MIC) values. Most isolates were inhibited by drug concentrations of 2-8 (CTZ), 1-4 (MCZ), or 16-32 (TBD) μg/mL. These results are partially in agreement with the findings of previous studies, in which substantially higher/lower MICs were occasionally reported. This is likely because of the different methodologies employed. Such discrepancies may not apply to clinical situations, where the compounds are applied topically.

CONCLUSION AND CLINICAL IMPORTANCE

The concept that clinical failure is linked to increased MICs is debatable, because significantly higher concentrations (in most cases at least 1,000 × the MIC) of the antifungals that were included in our study are routinely used in formulated products.