Aspergillus terreus: Novel lessons learned on amphotericin B resistance

Aspergillus fumigatus escape mechanisms from its harsh survival environments

Aspergillus fumigatus is a ubiquitous pathogenic mold and causes several diseases, including mycotoxicosis, allergic reactions, and systemic diseases (invasive aspergillosis), with high mortality rates. In its ecological niche, the fungus has evolved and mastered many reply strategies to resist and survive against negative threats, including harsh environmental stress and deficiency of essential nutrients from natural environments, immunity responses and drug treatments in host, and competition from symbiotic microorganisms. Hence, treating A. fumigatus infection is a growing challenge. In this review, we summarized A. fumigatus reply strategies and escape mechanisms and clarified the main competitive or symbiotic relationships between A. fumigatus, viruses, bacteria, or fungi in host microecology. Additionally, we discussed the contemporary drug repertoire used to treat A. fumigatus and the latest evidence of potential resistance mechanisms. This review provides valuable knowledge which will stimulate further investigations and clinical applications for treating and preventing A. fumigatus infections. KEY POINTS: • Harsh living environment was a great challenge for A. fumigatus survival. • A. fumigatus has evolved multiple strategies to escape host immune responses. • A. fumigatus withstands antifungal drugs via intrinsic escape mechanisms.

Stephanoascus ciferrii Complex: The Current State of Infections and Drug Resistance in Humans

In recent years, the incidence of fungal infections in humans has increased dramatically, accompanied by an expansion in the number of species implicated as etiological agents, especially environmental fungi never involved before in human infection. Among fungal pathogens, Candida species are the most common opportunistic fungi that can cause local and systemic infections, especially in immunocompromised individuals. Candida albicans (C. albicans) is the most common causative agent of mucosal and healthcare-associated systemic infections. However, during recent decades, there has been a worrying increase in the number of emerging multi-drug-resistant non-albicans Candida (NAC) species, i.e., C. glabrata, C. parapsilosis, C. tropicalis, C. krusei, C. auris, and C. ciferrii. In particular, Candida ciferrii, also known as Stephanoascus ciferrii or Trichomonascus ciferrii, is a heterothallic ascomycete yeast-like fungus that has received attention in recent decades as a cause of local and systemic fungal diseases. Today, the new definition of the S. ciferrii complex, which consists of S. ciferrii, Candida allociferrii, and Candida mucifera, was proposed after sequencing the 18S rRNA gene. Currently, the S. ciferrii complex is mostly associated with non-severe ear and eye infections, although a few cases of severe candidemia have been reported in immunocompromised individuals. Low susceptibility to currently available antifungal drugs is a rising concern, especially in NAC species. In this regard, a high rate of resistance to azoles and more recently also to echinocandins has emerged in the S. ciferrii complex. This review focuses on epidemiological, biological, and clinical aspects of the S. ciferrii complex, including its pathogenicity and drug resistance.

Aspergillus terreus spondylodiscitis following acupuncture and acupotomy in an immunocompetent host: case report and literature review

Aspergillus terreus is a fungus responsible for various infections in human beings; however, spine involvement is uncommon. Herein, we report a case of A. terreus spondylodiscitis following acupuncture and acupotomy in an immunocompetent Chinese patient. Admission lumbar magnetic resonance imaging (MRI) revealed infection at the L4/5 level without significant vertebral destruction. After unsuccessful symptomatic and anti-tuberculosis treatments, A. terreus was identified through culture, microscopy of isolate, histological examination and VITEK system. Intravenous voriconazole was then given; however, the patient's spinal condition deteriorated rapidly, resulting in evident destruction of the L4/5 vertebral bodies. Surgeries including L4/5 intervertebral disc debridement, spinal canal decompression, posterior lumbar interbody fusion (PLIF) with allogeneic fibula ring fusion cages, and posterior pedicle screw fixation were then performed. Imaging findings at one-month and six-month follow-up suggested that the patient was successfully treated. This case highlighted two important points: firstly, although acupuncture and acupotomy are generally regarded as safe conservative treatments for pain management, they can still lead to complications such as fungal spinal infection. Therefore, vigilance is necessary when considering these treatments; secondly, PLIF with allogeneic fibula ring fusion cages may be beneficial for A. terreus spondylodiscitis patients with spinal instability.

Antifungal resistance, combinations and pipeline: oh my!

Invasive fungal infections are a strong contributor to healthcare costs, morbidity and mortality, especially amongst hospitalized patients. Historically, Candida was responsible for approximately 15% of all nosocomial bloodstream infections. In the past 10 years, the epidemiology of Candida species has altered, with increasing prevalence of resistant species. With rising fungal resistance, especially in Candida spp., the demand for novel antifungal therapies has exponentially increased over the last decade. Newer antifungal agents have become an attractive option for patients needing long-term therapy for infections or those requiring antifungal prophylaxis. Despite advances in coverage of non-Candida pathogens with newer agents, clinical scenarios involving multidrug-resistant fungal pathogens continue to arise in practice. Combination antifungal therapy can lead to a host of side-effects, some of which can be drug limiting. Additional antifungal therapies with enhanced fungal spectrum of activity and decreased rates of adverse effects are warranted. Fosmanogepix, ibrexafungerp, olorofim and rezafungin may help fill some of these gaps in the antifungal armamentarium. This article is part of the Challenges and strategies in the management of invasive fungal infections Special Issue: https://www.drugsincontext.com/special_issues/challenges-and-strategies-in-the-management-of-invasive-fungal-infections.

Drug-Resistant Aspergillus spp.: A Literature Review of Its Resistance Mechanisms and Its Prevalence in Europe

Infections due to the Aspergillus species constitute an important challenge for human health. Invasive aspergillosis represents a life-threatening disease, mostly in patients with immune defects. Drugs used for fungal infections comprise amphotericin B, triazoles, and echinocandins. However, in the last decade, an increased emergence of azole-resistant Aspergillus strains has been reported, principally belonging to Aspergillus fumigatus species. Therefore, both the early diagnosis of aspergillosis and its epidemiological surveillance are very important to establish the correct antifungal therapy and to ensure a successful patient outcome. In this paper, a literature review is performed to analyze the prevalence of Aspergillus antifungal resistance in European countries. Amphotericin B resistance is observed in 2.6% and 10.8% of Aspergillus fumigatus isolates in Denmark and Greece, respectively. A prevalence of 84% of amphotericin B-resistant Aspergillus flavus isolates is reported in France, followed by 49.4%, 35.1%, 21.7%, and 20% in Spain, Portugal, Greece, and amphotericin B resistance of Aspergillus niger isolates is observed in Greece and Belgium with a prevalence of 75% and 12.8%, respectively. The prevalence of triazole resistance of Aspergillus fumigatus isolates, the most studied mold obtained from the included studies, is 0.3% in Austria, 1% in Greece, 1.2% in Switzerland, 2.1% in France, 3.9% in Portugal, 4.9% in Italy, 5.3% in Germany, 6.1% in Denmark, 7.4% in Spain, 8.3% in Belgium, 11% in the Netherlands, and 13.2% in the United Kingdom. The mechanism of resistance is mainly driven by the TR34/L98H mutation. In Europe, no in vivo resistance is reported for echinocandins. Future studies are needed to implement the knowledge on the spread of drug-resistant Aspergillus spp. with the aim of defining optimal treatment strategies.

Aspergillus terreus Antibody Serosurveillance in Tyrol: A Population-Based, Cross-Sectional Study of a Healthy Population

The rare, but emerging mold Aspergillus terreus is an important pathogen in some geographical areas, like Tyrol (Austria) and Houston (Texas). The reason for this high prevalence is unknown. The present serosurveillance study aimed to evaluate the trends in levels of A. terreus-specific IgG antibodies in various regions of Tyrol and to compare the results to the environmental spread of A. terreus in Tyrol. Therefore, 1058 serum samples from healthy blood donors were evaluated. Data revealed a significant difference between the Tyrolean Upland and Lowland. Moreover, female participants had higher A. terreus IgG antibody levels than male participants. The differences found in our study are consistent with the distributional differences in environmental and clinical samples described in previous studies, supporting that A. terreus IgG antibody levels reflect the environmental epidemiology of A. terreus in Tyrol.

Emerging Role of Sphingolipids in Amphotericin B Drug Resistance

Invasive fungal infections in humans are common in people with compromised immune systems and are difficult to treat, resulting in high mortality. Amphotericin B (AmB) is one of the main antifungal drugs available to treat these infections. AmB binds with plasma membrane ergosterol, causing leakage of cellular ions and promoting cell death. The increasing use of available antifungal drugs to combat pathogenic fungal infections has led to the development of drug resistance. AmB resistance is not very common and is usually caused by changes in the amount or type of ergosterol or changes in the cell wall. Intrinsic AmB resistance occurs in the absence of AmB exposure, whereas acquired AmB resistance can develop during treatment. However, clinical resistance arises due to treatment failure with AmB and depends on multiple factors such as the pharmacokinetics of AmB, infectious fungal species, and host immune status. Candida albicans is a common opportunistic pathogen that can cause superficial infections of the skin and mucosal surfaces, thrush, to life-threatening systemic or invasive infections. In addition, immunocompromised individuals are more susceptible to systemic infections caused by Candida, Aspergillus, and Cryptococcus. Several antifungal drugs with different modes of action are used to treat systemic to invasive fungal infections and are approved for clinical use in the treatment of fungal diseases. However, C. albicans can develop a variety of defenses against antifungal medications. In fungi, plasma membrane sphingolipid molecules could interact with ergosterol, which can lead to the alteration of drug susceptibilities such as AmB. In this review, we mainly summarize the role of sphingolipid molecules and their regulators in AmB resistance.

Antifungals: From Pharmacokinetics to Clinical Practice

The use of antifungal drugs started in the 1950s with polyenes nystatin, natamycin and amphotericin B-deoxycholate (AmB). Until the present day, AmB has been considered to be a hallmark in the treatment of invasive systemic fungal infections. Nevertheless, the success and the use of AmB were associated with severe adverse effects which stimulated the development of new antifungal drugs such as azoles, pyrimidine antimetabolite, mitotic inhibitors, allylamines and echinochandins. However, all of these drugs presented one or more limitations associated with adverse reactions, administration route and more recently the development of resistance. To worsen this scenario, there has been an increase in fungal infections, especially in invasive systemic fungal infections that are particularly difficult to diagnose and treat. In 2022, the World Health Organization (WHO) published the first fungal priority pathogens list, alerting people to the increased incidence of invasive systemic fungal infections and to the associated risk of mortality/morbidity. The report also emphasized the need to rationally use existing drugs and develop new drugs. In this review, we performed an overview of the history of antifungals and their classification, mechanism of action, pharmacokinetic/pharmacodynamic (PK/PD) characteristics and clinical applications. In parallel, we also addressed the contribution of fungi biology and genetics to the development of resistance to antifungal drugs. Considering that drug effectiveness also depends on the mammalian host, we provide an overview on the roles of therapeutic drug monitoring and pharmacogenomics as means to improve the outcome, prevent/reduce antifungal toxicity and prevent the emergence of antifungal resistance. Finally, we present the new antifungals and their main characteristics.

Potential Strategies to Control the Risk of Antifungal Resistance in Humans: A Comprehensive Review

Fungal infections are becoming one of the main causes of morbidity and mortality in people with weakened immune systems. Mycoses are becoming more common, despite greater knowledge and better treatment methods, due to the regular emergence of resistance to the antifungal medications used in clinical settings. Antifungal therapy is the mainstay of patient management for acute and chronic mycoses. However, the limited availability of antifungal drug classes limits the range of available treatments. Additionally, several drawbacks to treating mycoses include unfavourable side effects, a limited activity spectrum, a paucity of targets, and fungal resistance, all of which continue to be significant issues in developing antifungal drugs. The emergence of antifungal drug resistance has eliminated accessible drug classes as treatment choices, which significantly compromises the clinical management of fungal illnesses. In some situations, the emergence of strains resistant to many antifungal medications is a major concern. Although new medications have been developed to address this issue, antifungal drug resistance has grown more pronounced, particularly in patients who need long-term care or are undergoing antifungal prophylaxis. Moreover, the mechanisms that cause resistance must be well understood, including modifications in drug target affinities and abundances, along with biofilms and efflux pumps that diminish intracellular drug levels, to find novel antifungal drugs and drug targets. In this review, different classes of antifungal agents, and their resistance mechanisms, have been discussed. The latter part of the review focuses on the strategies by which we can overcome this serious issue of antifungal resistance in humans.

In Vitro Susceptibilities of Worldwide Isolates of Intrapulmonary Aspergillus Species and Important Candida Species in Sterile Body Sites against Important Antifungals: Data from the Antimicrobial Testing Leadership and Surveillance Program, 2017-2020

To understand the changes of resistance in clinically commonly encountered fungi, we used the Antimicrobial Testing Leadership and Surveillance (ATLAS) database to explore in vitro antifungal susceptibilities against clinically important isolates of Aspergillus and Candida species (collected from intrapulmonary and sterile body areas, respectively). We applied the CLSI antifungal 2020 and the EUCAST antifungal 2020 guidelines. From 2017 to 2020, isolates of intrapulmonary Aspergillus fumigatus (n = 660), Aspergillus niger (n = 107), Aspergillus flavus (n = 96), Aspergillus terreus (n = 40), and Aspergillus nidulans species complex (n = 26) and sterile site-originated isolates of Candida albicans (n = 1,810), Candida glabrata (n = 894), Candida krusei (n = 120), Candida dubliniensis (n = 107), Candida lusitaniae (n = 82), Candida guilliermondii (n = 28), and Candida auris (n = 7) were enrolled in this study. Using the EUCAST 2020 breakpoints, it was demonstrated that amphotericin B and posaconazole displayed poor in vitro susceptibility rates against A. fumigatus isolates (<50% and 18.9%, respectively). In contrast, isavuconazole and itraconazole showed high in vitro potency against most Aspergillus isolates (>92%). Most intrapulmonary Aspergillus isolates exhibited MICs of ≤0.06 μg/mL to anidulafungin. Furthermore, intrapulmonary A. fumigatus isolates collected from Italy and the United Kingdom exhibited lower in vitro susceptibility to isavuconazole (72.2% and 69%, respectively) than those in the remaining ATLAS participant countries (>85%). Higher isavuconazole MIC90s against C. auris and C. guilliermondii (1 and 4 μg/mL, respectively) were observed compared to the other five Candida species. Despite the aforementioned MICs and susceptibilities against fungi, research needs to consider the pharmacokinetic (PK) profiles, pharmacodynamic (PD) parameters, and clinical treatment experience with antifungals against specific Aspergillus species. IMPORTANCE In addition to monitoring the antifungal susceptibilities of clinically important fungi, reviewing the PK/PD indices and the clinical therapy experience of antifungals under evaluation are important to guide an appropriate antifungal prescription. The efficacies of liposomal amphotericin B complex and anidulafungin for the treatment of pulmonary aspergillosis caused by different Aspergillus species need to be periodically evaluated in the future.

Therapeutic Approaches for Combating Aspergillus Associated Infection

Now-a-days fungal infection emerges as a significant problem to healthcare management systems due to high frequency of associated morbidity, mortality toxicity, drug-drug interactions, and resistance of the antifungal agents. Aspergillus is the most common mold that cause infection in immunocompromised hosts. It's a hyaline mold that is cosmopolitan and ubiquitous in nature. Aspergillus infects around 10 million population each year with a mortality rate of 30-90%. Clinically available antifungal formulations are restricted to four classes (i.e., polyene, triazole, echinocandin, and allylamine), and each of them have their own limitations associated with the activity spectrum, the emergence of resistance, and toxicity. Consequently, novel antifungal agents with modified and altered chemical structures are required to combat these invasive fungal infections. To overcome these limitations, there is an urgent need for new antifungal agents that can act as potent drugs in near future. Currently, some compounds have shown effective antifungal activity. In this review article, we have discussed all potential antifungal therapies that contain old antifungal drugs, combination therapies, and recent novel antifungal formulations, with a focus on the Aspergillus associated infections.

Molecular Mechanisms of Antifungal Resistance in Mucormycosis

Mucormycosis is one among the life-threatening fungal infections with high morbidity and mortality. It is an uncommon and rare infection targeting people with altered immunity. This lethal infection induced by fungi belonging to the Mucorales family is very progressive in nature. The incidence has increased in recent decades owing to the rise in immunocompromised patients. Disease management involves a multimodal strategy including early administration of drugs and surgical removal of infected tissues. Among the antifungals, azoles and amphotericin B remain the gold standard drugs of choice for initial treatment. The order Mucorales are developing a high level of resistance to the available systemic antifungal drugs, and the efficacy still remains below par. Deciphering the molecular mechanisms behind the antifungal resistance in Mucormycosis would add vital information to our available antifungal armamentarium and design novel therapies. Therefore, in this review, we have discussed the mechanisms behind Mucormycosis antifungal resistance. Moreover, this review also highlights the basic mechanisms of action of antifungal drugs and the resistance landscape which is expected to augment future treatment strategies.

Amphotericin B resistance in Leishmania mexicana: Alterations to sterol metabolism and oxidative stress response

Amphotericin B is increasingly used in treatment of leishmaniasis. Here, fourteen independent lines of Leishmania mexicana and one L. infantum line were selected for resistance to either amphotericin B or the related polyene antimicrobial, nystatin. Sterol profiling revealed that, in each resistant line, the predominant wild-type sterol, ergosta-5,7,24-trienol, was replaced by other sterol intermediates. Broadly, two different profiles emerged among the resistant lines. Whole genome sequencing then showed that these distinct profiles were due either to mutations in the sterol methyl transferase (C24SMT) gene locus or the sterol C5 desaturase (C5DS) gene. In three lines an additional deletion of the miltefosine transporter gene was found. Differences in sensitivity to amphotericin B were apparent, depending on whether cells were grown in HOMEM, supplemented with foetal bovine serum, or a serum free defined medium (DM). Metabolomic analysis after exposure to AmB showed that a large increase in glucose flux via the pentose phosphate pathway preceded cell death in cells sustained in HOMEM but not DM, indicating the oxidative stress was more significantly induced under HOMEM conditions. Several of the lines were tested for their ability to infect macrophages and replicate as amastigote forms, alongside their ability to establish infections in mice. While several AmB resistant lines showed reduced virulence, at least two lines displayed heightened virulence in mice whilst retaining their resistance phenotype, emphasising the risks of resistance emerging to this critical drug.

EUCAST-Obtained Olorofim MICs against Aspergillus and Scedosporium Species and Lomentospora prolificans Showed High Agreements between Visual Inspection and Spectrophotometric Readings

Previous studies show high agreement between MIC spectrophotometric readings and visual inspection of azoles and amphotericin B against Aspergillus fumigatus isolates. Here, we tested and compared the in vitro activity of a novel antifungal, olorofim, against Aspergillus spp., Scedosporium spp., and Lomentospora prolificans by visual inspection and spectrophotometric readings. Clinical isolates of Aspergillus (n = 686) and Scedosporium (n = 36) spp. and L. prolificans (n = 13) were tested. Olorofim MICs were evaluated-following the EUCAST E.Def 9.4 procedure-by visual inspection or spectrophotometric readings (combinations of either ≥90% or ≥95% fungal growth inhibition endpoints compared to drug-free control endpoints and different wavelengths [405 nm, 450 nm, 492 nm, 540 nm, and 620 nm]). We observed high in vitro activity of olorofim against all tested Aspergillus spp. (MICs up to 0.06 mg/L), except for A. calidoustus, and against L. prolificans and Scedosporium spp. (MICs up to 0.125 mg/L). The combination of ≥90% fungal growth inhibition endpoints at wavelengths of ≥492 nm resulted in high essential agreements with A. fumigatus and lesser agreement with non-fumigatus Aspergillus, Scedosporium spp., and L. prolificans, although the number of isolates studied was low. This single-center study shows high agreement among olorofim MICs against A. fumigatus by visual inspection and spectrophotometric readings (≥90% fungal growth inhibition endpoints and wavelengths of ≥492 nm) and encouraging results against non-fumigatus Aspergillus spp., Scedosporium spp., and L. prolificans.

Species Identification and In Vitro Antifungal Susceptibility of Paecilomyces/Purpureocillium Species Isolated from Clinical Respiratory Samples: A Multicenter Study

Paecilomyces spp. are emerging fungal pathogens, where Paecilomyces lilacinus and Paecilomyces variotii are the most reported species. Taxonomic and phylogenetic revisions in this genus have shown that P. variotii represents a species complex, whereas P. lilacinus is related to another genus called Purpureocillium. The aims of this study were to identify clinical isolates of Paecilomyces spp. at the species level, and to determine their antifungal susceptibility profiles. 70 clinical Paecilomyces spp. isolates were identified by MALDI-TOF Mass Spectrometry (MS) and by multilocus rDNA genes sequencing including ITS and the D1/D2 genes. Among the 70 Paecilomyces spp. isolates, 28 were identified as P. lilacinum, 26 as P. variotii stricto sensu, and 16 as P. maximus. For antifungal susceptibility testing, Minimal Inhibitory Concentrations (MICs) or Minimal Effective Concentrations (MECs) were determined for 8 antifungals. All P. lilacinum isolates had high MICs and MECs of amphotericin B and echinocandins, respectively, unlike P. variotii and P. maximus. For azole drugs, MICs were molecule- and species- dependent. The differences in in vitro susceptibility to antifungals underline the importance of accurate species identification. The MALDI–TOF MS can be a good alternative in routine laboratory to ensure fast identification of Paecilomyces spp. and P. lilacinum.

A Silent Threat of Emerging Resistance Based on Antifungal Susceptibility Pattern of Filamentous Fungi by Microdilution, E Test and, Disc Diffusion Method: A Critical Constructive Analysis

For more than two decades, antifungal susceptibility testing and interpretation haunted the medical professionals in diagnostics and management. This article mainly focuses on the three most widely used methods: broth microdilution, E test, and disc diffusion. It also focuses on the fact that clinicians should switch from empirical treatment to susceptible drugs as early as possible to combat antifungal resistance and newer mutations that horrify us every single day with poor patient outcomes. Many factors need to be taken into account during the interpretation of results but the positive side of the story is that they have been well documented in the literature. Though many methods have come up in testing antifungal susceptibility, still there is a scope for a rapid yet accurate testing modality to flourish and take the lead.

Fungal Infections as an Uprising Threat to Human Health: Chemosensitization of Fungal Pathogens With AFP From Aspergillus giganteus

Occurrence and intensity of systemic invasive fungal infections have significantly risen in recent decades with large amount of mortality and morbidity rates at global level. Treatment therapy lies on the current antifungal interventions and are often limited due to the emergence of resistance to antifungal agents. Chemosensitization of fungal strains to the conventional antimycotic drugs are of growing concern. Current antifungal drugs often have been reported with poor activity and side effects to the host and have a few number of targets to manifest their efficacy on the pathogens. Indiscriminately, the aforementioned issues have been easily resolved by the development of new intervention strategies. One such approach is to employ combinational therapy that has exhibited a great level of inhibitions than that of a single compound. Chemosensitization of pathogenic mycoses to commercial antifungal drugs could be drastically enhanced by co-application of chemosensitizers along with the conventional drugs. Chemosensitizers could address the resistance mechanisms evolved in the pathogenic fungi and targeting the system to make the organism susceptible to commercially and clinically proven antifungal drugs. However, this strategy has not been overreached to the greater level, but it needs much attention to fight against not only with the pathogen but combat the resistance mechanisms of pathogens to drugs. Natural compounds including plant compounds and microbial proteins act as potential chemosensitizers to break the resistance in mycoses. Aspergillus giganteus, a filamentous fungus, is known to produce a cysteine rich extracellular protein called as antifungal protein (AFP). AFP has shown enhanced efficacy against several filamentous and non-filamentous fungal pathogens. On the basis of the reported studies on its targeted potential against pathogenic mycoses, AFP would be fabricated as a good chemosensitizer to augment the fungicidal efficacy of commercial antimycotic drugs. This paper reviews on breakthrough in the discovery of antifungal drugs along with the resistance patterns of mycoses to commercial drugs followed by the current intervention strategies applied to augment the fungicidal potential of drugs.

Experimental Evolution of Multidrug Resistance in Neurospora crassa under Antifungal Azole Stress

Multidrug resistance, defined as the resistance to multiple drugs in different categories, has been an increasing serious problem. Limited antifungal drugs and the rapid emergence of antifungal resistance prompt a thorough understanding of how the occurrence of multidrug resistance develops and which mechanisms are involved. In this study, experimental evolution was performed under single-azole-drug stress with the model filamentous fungus Neurospora crassa. By about 30 weeks of continuous growth on agar plates containing ketoconazole or voriconazole with weekly transfer, four evolved multidrug-resistant strains 30thK1, 30thK2, 26thV1, and 24thV2 were obtained. Compared to the ancestral strain, all four strains increased resistance not only to commonly used azoles, including ketoconazole, voriconazole, itraconazole, fluconazole, and triadimefon, but also to antifungal drugs in other categories, including terbinafine (allylamine), amorolfine (morpholine), amphotericin B (polyene), polyoxin B (chitin synthesis inhibitor), and carbendazim (β-tubulin inhibitor). After 8 weeks of growth on agar plates without antifungal drugs with weekly transfer, these evolved strains still displayed multidrug-resistant phenotype, suggesting the multidrug resistance could be stably inherited. Transcriptional measurement of drug target genes and drug transporter genes and deletion analysis of the efflux pump gene cdr4 in the evolved strains suggest that overexpression of cdr4 played a major role in the resistance mechanisms for azoles and terbinafine in the evolved strains, particularly for 30thK2 and 26thV1, and evolved drug-resistant strains had less intracellular ketoconazole accumulation and less disruption of ergosterol accumulations under ketoconazole stress compared to wild type. Mutations specifically present in evolved drug-resistant strains were identified by genome re-sequencing, and drug susceptibility test of knockout mutants for most of mutated genes suggests that mutations in 16 genes, functionally novel in drug resistance, potentially contribute to multidrug resistance in evolved strains.

The accuracy and clinical impact of the morphological identification of Aspergillus species in the age of cryptic species: A single-centre study

BACKGROUND

Aspergillus spp. is identified morphologically without antifungal susceptibility tests (ASTs) in most clinical laboratories. The aim of this study was to examine the clinical impact of the morphological identification of Aspergillus spp. to ensure the adequate clinical management of Aspergillus infections.

PATIENTS/METHODS

Aspergillus isolates (n = 126) from distinct antifungal treatment-naïve patients with aspergillosis were first identified morphologically, followed by species-level identification via DNA sequencing. An AST for itraconazole (ITC) and voriconazole (VRC) was performed on each Aspergillus isolate.

RESULTS

Based on the genetic test results, morphology-based identification was accurate for >95% of the isolates at the species sensu lato level although the test concordance of Aspergillus spp. with low detection rates was low. The rates of cryptic species were found to be 1.2% among the isolates of A. fumigatus complex and 96.8% in the A. niger complex. Cryptic species with lower susceptibilities to antifungal drugs than sensu stricto species among the same Aspergillus section were as follows: The A. lentulus (n = 1) isolates had low susceptibilities to azoles among the A. fumigatus complex species (n = 86), and A. tubingensis isolates (n = 18) exhibited lower susceptibility to azoles among the A. niger complex species (n = 31).

CONCLUSION

Diagnostic accuracy was high at the A. fumigatus and A. niger complex level. However, in the presence of cryptic species, a solely morphological identification was insufficient. Particularly, ITC and VRC might be inappropriate for aspergillosis treatment when the A. niger complex is identified morphologically because it is possible that the Aspergillus isolate is A. tubingensis.

Fungal Genomics in Respiratory Medicine: What, How and When?

Respiratory infections caused by fungal pathogens present a growing global health concern and are a major cause of death in immunocompromised patients. Worryingly, coronavirus disease-19 (COVID-19) resulting in acute respiratory distress syndrome has been shown to predispose some patients to airborne fungal co-infections. These include secondary pulmonary aspergillosis and mucormycosis. Aspergillosis is most commonly caused by the fungal pathogen Aspergillus fumigatus and primarily treated using the triazole drug group, however in recent years, this fungus has been rapidly gaining resistance against these antifungals. This is of serious clinical concern as multi-azole resistant forms of aspergillosis have a higher risk of mortality when compared against azole-susceptible infections. With the increasing numbers of COVID-19 and other classes of immunocompromised patients, early diagnosis of fungal infections is critical to ensuring patient survival. However, time-limited diagnosis is difficult to achieve with current culture-based methods. Advances within fungal genomics have enabled molecular diagnostic methods to become a fast, reproducible, and cost-effective alternative for diagnosis of respiratory fungal pathogens and detection of antifungal resistance. Here, we describe what techniques are currently available within molecular diagnostics, how they work and when they have been used.

The Elevated Endogenous Reactive Oxygen Species Contribute to the Sensitivity of the Amphotericin B-Resistant Isolate of Aspergillus flavus to Triazoles and Echinocandins

Aspergillus flavus has been frequently reported as the second cause of invasive aspergillosis (IA), as well as the leading cause in certain tropical countries. Amphotericin B (AMB) is a clinically important therapy option for a range of invasive fungal infections including invasive aspergillosis, and in vitro resistance to AMB was associated with poor outcomes in IA patients treated with AMB. Compared with the AMB-susceptible isolates of A. terreus, the AMB-resistant isolates of A. terreus showed a lower level of AMB-induced endogenous reactive oxygen species (ROS), which was an important cause of AMB resistance. In this study, we obtained one AMB-resistant isolate of A. flavus, with an AMB MIC of 32 μg/mL, which was sensitive to triazoles and echinocandins. This isolate presented elevated endogenous ROS levels, which strongly suggested that no contribution of decreased AMB-induced endogenous ROS for AMB-resistance, opposite to those observed in A. terreus. Further, we confirmed that the elevated endogenous ROS contributed to the sensitivity of the AMB-resistant A. flavus isolate to triazoles and echinocandins. Further investigation is needed to elucidate the causes of elevated endogenous ROS and the resistance mechanism to AMB in A. flavus.

Aspergillus terreus Species Complex

Infections due to Aspergillus species are an acute threat to human health; members of the Aspergillus section Fumigati are the most frequently occurring agents, but depending on the local epidemiology, representatives of section Terrei or section Flavi are the second or third most important. Aspergillus terreus species complex is of great interest, as it is usually amphotericin B resistant and displays notable differences in immune interactions in comparison to Aspergillus fumigatus. The latest epidemiological surveys show an increased incidence of A. terreus as well as an expanding clinical spectrum (chronic infections) and new groups of at-risk patients being affected. Hallmarks of these non-Aspergillus fumigatus invasive mold infections are high potential for tissue invasion, dissemination, and possible morbidity due to mycotoxin production. We seek to review the microbiology, epidemiology, and pathogenesis of A. terreus species complex, address clinical characteristics, and highlight the underlying mechanisms of amphotericin B resistance. Selected topics will contrast key elements of A. terreus with A. fumigatus. We provide a comprehensive resource for clinicians dealing with fungal infections and researchers working on A. terreus pathogenesis, aiming to bridge the emerging translational knowledge and future therapeutic challenges on this opportunistic pathogen.

Resistance to Antifungal Drugs

Pathogenic fungi have several mechanisms of resistance to antifungal drugs, driven by the genetic plasticity and versatility of their homeostatic responses to stressful environmental cues. We critically review the molecular mechanisms of resistance and cellular adaptations of pathogenic fungi in response to antifungals and discuss the factors contributing to such resistance. We offer suggestions for the translational and clinical research agenda of this rapidly evolving and medically important field. A better understanding of antifungal resistance should assist in developing better detection tools and inform optimal strategies for preventing and treating refractory mycoses in the future.

Species identification and antifungal susceptibility testing of Aspergillus strains isolated from patients with otomycosis in northern China

BACKGROUND/PURPOSE

There are limited studies on species distribution and susceptibility profiles of Aspergillus strains isolated from patients with otomycosis in China.

METHODS

A total of 69 confirmed Aspergillus species isolates were obtained from ear swabs of patients diagnosed with otomycosis from 2017 to 2018 in northern China. Identification of these Aspergillus isolates at the species level was performed using conventional morphological methods and MALDI-TOF MS in combination with molecular sequencing, and in vitro susceptibility to nine antifungal agents was evaluated using the Sensititre YeastOne system.

RESULTS

The Aspergillus section Nigri had the greatest distribution of Aspergillus isolates. A. welwitschiae (n = 25) was the most predominant isolate in section Nigri, followed by A. tubingensis (n = 12) and A. niger (n = 11). Other Aspergillus species were also isolated, including A. terreus (n = 11), A. flavus/A. oryzae (n = 8), and A. fumigatus (n = 2). Amphotericin B, posaconazole, and echinocandins were highly in vitro active against all the isolates tested. 2.9% (2/69) of the isolates were resistant to azoles in our study, including one A. niger isolate with a high MIC value for itraconazole (ITR) (16 mg/L) and one A. tubingensis isolate cross-resistant to both voriconazole (VOR) (MIC >8 mg/L) and ITR (MIC >16 mg/L). One A. welwitschiae and one A. niger isolate both had increased MIC values of 4 mg/L against VOR.

CONCLUSIONS

A. welwitschiae was the most prevalent Aspergillus species isolated from patients with otomycosis. Our findings also indicated that the azole-resistant Aspergillus section Nigri should be utilized to guide clinical medication for Otomycosis.

Gender differences in acute toxicity, toxicokinetic and tissue distribution of amphotericin B liposomes in rats

Amphotericin B (AmB), an effective polyene drug with broad spectrum antifungal activity, is used for serious fungal infections. Liposomal amphotericin B (LAmB) is a lipid dosage form, which has a significantly improved toxicity profile compared with conventional amphotericin B deoxycholate (DAmB). This study focused on verifying the gender differences in the acute toxicity of LAmB and further exploring its causes. Acute toxicity study of LAmB and DAmB were performed in rats, and toxicity responses and mortality of different sexes were observed and recorded. Concentrations of AmB in rat plasma and tissues were determined by a fully validated UPLC-MS/MS assay. The results demonstrated that LAmB showed significant gender differences in acute toxicity, with more severe toxic symptoms and higher mortality for female rats at different doses, but the same differences were not observed for DAmB under the same condition. To explore the cause of differences, toxicokinetic and tissue distribution studies were performed and the results showed that female animals had higher drug exposure, longer half-life and lower plasma clearance compared to male rats, and the drug was mostly distributed in the liver and kidneys, in which female rats displayed a significant higher concentration than that of male rats.

Dexamethasone Promotes Aspergillus fumigatus Growth in Macrophages by Triggering M2 Repolarization via Targeting PKM2

Since long-term corticosteroid treatment is associated with emerging opportunistic fungal infections causing high morbidity and mortality in immune-suppressed individuals, here we characterized the impact of dexamethasone (Dex) treatment on Aspergillus fumigatus-related immune modulation. We found by high content screening and flow cytometric analyses that during monocyte-to-macrophage differentiation, as little as 0.1 µg/mL Dex resulted in a shift in macrophage polarization from M1 to M2-like macrophages. This macrophage repolarization mediated via Dex was characterized by significant upregulation of the M2 marker CD163 and downmodulation of M1 markers CD40 and CD86 as well as changes in phenotypic properties and adherence. These Dex-mediated phenotypic alterations were furthermore associated with a metabolic switch in macrophages orchestrated via PKM2. Such treated macrophages lost their ability to prevent Aspergillus fumigatus germination, which was correlated with accelerated fungal growth, destruction of macrophages, and induction of an anti-inflammatory cytokine profile. Taken together, repolarization of macrophages following corticosteroid treatment and concomitant switch to an anti-inflammatory phenotype might play a prominent role in triggering invasive aspergillosis (IA) due to suppression of innate immunological responses necessary to combat extensive fungal outgrowth.

Trends on Aspergillus Epidemiology-Perspectives from a National Reference Laboratory Surveillance Program

Identification of Aspergillus to species level is important since sibling species may display variable susceptibilities to multiple antifungal drugs and also because correct identification contributes to improve the knowledge of epidemiological studies. Two retrospective laboratory studies were conducted on Aspergillus surveillance at the Portuguese National Mycology Reference Laboratory. The first, covering the period 2017–2018, aimed to study the molecular epidemiology of 256 Aspergillus isolates obtained from patients with respiratory, subcutaneous, or systemic infections and from environmental samples. The second, using our entire collection of clinical and environmental A. fumigatus isolates (N = 337), collected between 2012 and 2019, aimed to determine the frequency of azole-resistant A. fumigatus isolates. Aspergillus fumigatus sensu stricto was the most frequent species in both clinical and environmental samples. Overall, and considering all Aspergillus sections identified, a high frequency of cryptic species was detected, based on beta-tubulin or calmodulin sequencing (37% in clinical and 51% in environmental isolates). Regarding all Fumigati isolates recovered from 2012–2019, the frequency of cryptic species was 5.3% (18/337), with the identification of A. felis (complex), A. lentulus, A. udagawae, A. hiratsukae, and A. oerlinghauensis. To determine the frequency of azole resistance of A. fumigatus, isolates were screened for azole resistance using azole-agars, and 53 possible resistant isolates were tested by the CLSI microdilution reference method. Nine A. fumigatus sensu stricto and six Fumigati cryptic isolates showed high minimal inhibitory concentrations to itraconazole, voriconazole, and/or posaconazole. Real-time PCR to detect cyp51A mutations and sequencing of cyp51A gene and its promoter were performed. The overall frequency of resistance to azoles in A. fumigatus sensu stricto was 3.0%. With this retrospective analysis, we were able to detect one azole-resistant G54R mutant A. fumigatus environmental isolate, collected in 2015. The TR₃₄/L98H mutation, linked to environmental transmission route of azole resistance, was the most frequently detected mutation (N = 4; 1.4%). Our findings underline the demand for correct identification and susceptibility testing of Aspergillus isolates.

Amphotericin B and Other Polyenes-Discovery, Clinical Use, Mode of Action and Drug Resistance

Although polyenes were the first broad spectrum antifungal drugs on the market, after 70 years they are still the gold standard to treat a variety of fungal infections. Polyenes such as amphotericin B have a controversial image. They are the antifungal drug class with the broadest spectrum, resistance development is still relatively rare and fungicidal properties are extensive. Yet, they come with a significant host toxicity that limits their use. Relatively recently, the mode of action of polyenes has been revised, new mechanisms of drug resistance were discovered and emergent polyene resistant species such as Candida auris entered the picture. This review provides a short description of the history and clinical use of polyenes, and focusses on the ongoing debate concerning their mode of action, the diversity of resistance mechanisms discovered to date and the most recent trends in polyene resistance development.

The Quiet and Underappreciated Rise of Drug-Resistant Invasive Fungal Pathogens

Human fungal pathogens are attributable to a significant economic burden and mortality worldwide. Antifungal treatments, although limited in number, play a pivotal role in decreasing mortality and morbidities posed by invasive fungal infections (IFIs). However, the recent emergence of multidrug-resistant Candida auris and Candida glabrata and acquiring invasive infections due to azole-resistant C. parapsilosis, C. tropicalis, and Aspergillus spp. in azole-naïve patients pose a serious health threat considering the limited number of systemic antifungals available to treat IFIs. Although advancing for major fungal pathogens, the understanding of fungal attributes contributing to antifungal resistance is just emerging for several clinically important MDR fungal pathogens. Further complicating the matter are the distinct differences in antifungal resistance mechanisms among various fungal species in which one or more mechanisms may contribute to the resistance phenotype. In this review, we attempt to summarize the burden of antifungal resistance for selected non-albicansCandida and clinically important Aspergillus species together with their phylogenetic placement on the tree of life. Moreover, we highlight the different molecular mechanisms between antifungal tolerance and resistance, and comprehensively discuss the molecular mechanisms of antifungal resistance in a species level.

Combat trauma-related invasive fungal wound infections

Purpose of review

This review highlights research from the past five years on combat trauma-related invasive fungal wound infections (IFIs) with a focus on risk stratification to aid patient management, microbiology, and diagnostics.

Recent Findings

A revised classification scheme stratifies wounds into three risk groups: IFI, High Suspicion of IFI, and Low Suspicion of IFI. This stratification is based on persistence of wound necrosis and laboratory fungal evidence, presence of signs/symptoms of deep soft-tissue infections, and the need for antifungals. Use of this classification could allow for prioritization of antifungal therapy. Further, IFIs delay wound healing, particularly when caused by fungi of the order Mucorales. Lastly, molecular sequencing offers promising and complimentary results to the gold standard histopathology.

Summary

Optimal management of combat-related IFIs depends on early tissue-based diagnosis with aggressive surgical debridement and concomitant dual antifungal therapy. Further research on clinical decision support tools and rapid diagnostics are needed.

A 9-Year Experience of Aspergillus Infections from Isfahan, Iran

Purpose

Aspergillosis is an important fungal disease affecting millions of individuals worldwide. The genus of Aspergillus consist of various complexes, causing a wide spectrum of diseases from superficial infections in immunocompetent hosts to life-threatening disseminated infections among immunocompromised patients. This study aimed to identify Aspergillus species by phenotypic (total isolates) and molecular tests (35 isolates), obtained from patients in Isfahan (the third-largest city of Iran) between 2010 and 2018, and determine the susceptibility of 35 clinical isolates to itraconazole (ITR), amphotericin-B (AMB), and voriconazole (VOR).

Patients and Methods

Based on clinical signs, a total of 2385 suspected cases were included in this retrospective study from January 2010 to December 2018. Direct microscopic examination with potassium hydroxide, sabouraud dextrose agar with chloramphenicol, and czapekdox agar media was applied to identify etiologic agents. Thirty-five Aspergillus species collected from January 2016 to December 2018 were identified by PCR-sequencing of ITS1-5.8SrDNA-ITS2 region, and their susceptibility to ITR, AMB, and VOR was determined using E-test.

Results

Based on direct microscopy and positive culture, 132 out of 2385 suspected cases had Aspergillus infection (5.5%). Fifty-four patients were male, and 78 patients were female. Patients in the age groups of 41–50 and 21–30 years had the highest and lowest frequencies, respectively. Aspergillus flavus/oryzae (n=54), A. fumigatus (n=24), A. niger (n=15), and A. terreus (n=12) were the most prevalent Aspergillus species, respectively. Among 35 Aspergillus species, the MIC ranges of AMB, ITR, and VOR for A. flavus/oryzae, A. niger, and A. terreus were (0.5–4 μg/mL; 0.5–16 μg/mL; 0.25–8 μg/mL), (1 μg/mL, 1 μg/mL, 1 μg/mL), and (4–4 μg/mL, 0.5–1 μg/mL, 0.5–1 μg/mL), respectively.

Conclusion

Aspergillus infections have a wide spectrum of clinical manifestations and often occur in immunocompromised patients. Accurate identification at the species level is essential since the emergence of cryptic species is connected to different patterns of AFST that affect patient treatment outcomes. Azole-resistant Aspergillus spp. is a global concern, and the detection of the route of resistance is pivotal to prevent and control infection.

In Vitro Evaluation of Radiolabeled Amphotericin B for Molecular Imaging of Mold Infections

Invasive pulmonary aspergillosis and mucormycosis are life-threatening complications in immunocompromised patients. A rapid diagnosis followed by early antifungal treatment is essential for patient survival. Given the limited spectrum of biomarkers for invasive mold infections, recent studies have proposed the use of radiolabeled siderophores or antibodies as molecular probes to increase the specificity of radiological findings by nuclear imaging modalities. While holding enormous diagnostic potential, most of the currently available molecular probes are tailored to the detection of Aspergillus species, and their cost-intensive and sophisticated implementation restricts their accessibility at less specialized centers. In order to develop cost-efficient and broadly applicable tracers for pulmonary mold infections, this study established streamlined and high-yielding protocols to radiolabel amphotericin B (AMB) with the gamma emitter technetium-99m (^99mTc-AMB) and the positron emitter gallium-68 (⁶⁸Ga-AMB). The radiochemical purity of the resulting tracers consistently exceeded 99%, and both probes displayed excellent stability in human serum (>98% after 60 to 240 min at 37°C). The uptake kinetics by representative mold pathogens were assessed in an in vitro Transwell assay using infected endothelial cell layers. Both tracers accumulated intensively and specifically in Transwell inserts infected with Aspergillus fumigatus, Rhizopus arrhizus, and other clinically relevant mold pathogens compared with their accumulation in uninfected inserts and inserts infected with bacterial controls. Inoculum-dependent enrichment was confirmed by gamma counting and autoradiographic imaging. Taken together, this pilot in vitro study proposes ^99mTc-AMB and ⁶⁸Ga-AMB to be facile, stable, and specific probes, meriting further preclinical in vivo evaluation of radiolabeled amphotericin B for molecular imaging in invasive mycoses.

Genomic and Phenotypic Heterogeneity of Clinical Isolates of the Human Pathogens Aspergillus fumigatus, Aspergillus lentulus, and Aspergillus fumigatiaffinis

Fungal pathogens are a global threat to human health. For example, fungi from the genus Aspergillus cause a spectrum of diseases collectively known as aspergillosis. Most of the >200,000 life-threatening aspergillosis infections per year worldwide are caused by Aspergillus fumigatus. Recently, molecular typing techniques have revealed that aspergillosis can also be caused by organisms that are phenotypically similar to A. fumigatus but genetically distinct, such as Aspergillus lentulus and Aspergillus fumigatiaffinis. Importantly, some of these so-called cryptic species are thought to exhibit different virulence and drug susceptibility profiles than A. fumigatus, however, our understanding of their biology and pathogenic potential has been stymied by the lack of genome sequences and phenotypic profiling of multiple clinical strains. To fill this gap, we phenotypically characterized the virulence and drug susceptibility of 15 clinical strains of A. fumigatus, A. lentulus, and A. fumigatiaffinis from Spain and sequenced their genomes. We found heterogeneity in drug susceptibility across species and strains. We further found heterogeneity in virulence within each species but no significant differences in the virulence profiles between the three species. Genes known to influence drug susceptibility (cyp51A and fks1) vary in paralog number and sequence among these species and strains and correlate with differences in drug susceptibility. Similarly, genes known to be important for virulence in A. fumigatus showed variability in number of paralogs across strains and across species. Characterization of the genomic similarities and differences of clinical strains of A. lentulus, A. fumigatiaffinis, and A. fumigatus that vary in disease-relevant traits will advance our understanding of the variance in pathogenicity between Aspergillus species and strains that are collectively responsible for the vast majority of aspergillosis infections in humans.

New Approaches for Cryptococcosis Treatment

Cryptococcosis is an important opportunistic infection and a leading cause of meningitis in patients with HIV infection. The antifungal pharmacological treatment is limited to amphotericin B, fluconazole and 5- flucytosine. In addition to the limited pharmacological options, the high toxicity, increased resistance rate and difficulty of the currently available antifungal molecules to cross the blood-brain barrier hamper the treatment. Thus, the search for new alternatives for the treatment of cryptococcal meningitis is extremely necessary. In this review, we describe the therapeutic strategies currently available, discuss new molecules with antifungal potential in different phases of clinical trials and in advanced pre-clinical phase, and examine drug nanocarriers to improve delivery to the central nervous system.

Antifungal Drugs

We reviewed the licensed antifungal drugs and summarized their mechanisms of action, pharmacological profiles, and susceptibility to specific fungi. Approved antimycotics inhibit 1,3-β-d-glucan synthase, lanosterol 14-α-demethylase, protein, and deoxyribonucleic acid biosynthesis, or sequestrate ergosterol. Their most severe side effects are hepatotoxicity, nephrotoxicity, and myelotoxicity. Whereas triazoles exhibit the most significant drug–drug interactions, echinocandins exhibit almost none. The antifungal resistance may be developed across most pathogens and includes drug target overexpression, efflux pump activation, and amino acid substitution. The experimental antifungal drugs in clinical trials are also reviewed. Siderophores in the Trojan horse approach or the application of siderophore biosynthesis enzyme inhibitors represent the most promising emerging antifungal therapies.

Molecular Mechanisms of Conidial Germination in Aspergillus spp

Aspergilli produce conidia for reproduction or to survive hostile conditions, and they are highly effective in the distribution of conidia through the environment. In immunocompromised individuals, inhaled conidia can germinate inside the respiratory tract, which may result in invasive pulmonary aspergillosis. The management of invasive aspergillosis has become more complex, with new risk groups being identified and the emergence of antifungal resistance. Patient survival is threatened by these developments, stressing the need for alternative therapeutic strategies. As germination is crucial for infection, prevention of this process might be a feasible approach. A broader understanding of conidial germination is important to identify novel antigermination targets. In this review, we describe conidial resistance against various stresses, transition from dormant conidia to hyphal growth, the underlying molecular mechanisms involved in germination of the most common Aspergillus species, and promising antigermination targets. Germination of Aspergillus is characterized by three morphotypes: dormancy, isotropic growth, and polarized growth. Intra- and extracellular proteins play an important role in the protection against unfavorable environmental conditions. Isotropically expanding conidia remodel the cell wall, and biosynthetic machineries are needed for cellular growth. These biosynthetic machineries are also important during polarized growth, together with tip formation and the cell cycle machinery. Genes involved in isotropic and polarized growth could be effective antigermination targets. Transcriptomic and proteomic studies on specific Aspergillus morphotypes will improve our understanding of the germination process and allow discovery of novel antigermination targets and biomarkers for early diagnosis and therapy.

Comparison of Antibiotic Resistance Mechanisms in Antibiotic-Producing and Pathogenic Bacteria

Antibiotic resistance poses a tremendous threat to human health. To overcome this problem, it is essential to know the mechanism of antibiotic resistance in antibiotic-producing and pathogenic bacteria. This paper deals with this problem from four points of view. First, the antibiotic resistance genes in producers are discussed related to their biosynthesis. Most resistance genes are present within the biosynthetic gene clusters, but some genes such as paromomycin acetyltransferases are located far outside the gene cluster. Second, when the antibiotic resistance genes in pathogens are compared with those in the producers, resistance mechanisms have dependency on antibiotic classes, and, in addition, new types of resistance mechanisms such as Eis aminoglycoside acetyltransferase and self-sacrifice proteins in enediyne antibiotics emerge in pathogens. Third, the relationships of the resistance genes between producers and pathogens are reevaluated at their amino acid sequence as well as nucleotide sequence levels. Pathogenic bacteria possess other resistance mechanisms than those in antibiotic producers. In addition, resistance mechanisms are little different between early stage of antibiotic use and the present time, e.g., β-lactam resistance in Staphylococcus aureus. Lastly, guanine + cytosine (GC) barrier in gene transfer to pathogenic bacteria is considered. Now, the resistance genes constitute resistome composed of complicated mixture from divergent environments.

Treatment of Infections Due to Aspergillus terreus Species Complex

The Aspergillus terreus species complex is found in a wide variety of habitats, and the spectrum of diseases caused covers allergic bronchopulmonary aspergillosis, Aspergillus bronchitis and/or tracheobronchitis, and invasive and disseminated aspergillosis. Invasive infections are a significant cause of morbidity and mortality mainly in patients with hematological malignancy. The section Terrei covers a total of 16 accepted species of which most are amphotericin B resistant. Triazoles are the preferred agents for treatment and prevention of invasive aspergillosis. Poor prognosis in patients with invasive A. terreus infections seems to be independent of anti-Aspergillus azole-based treatment.