Clinical Azoles Research Articles

Most azole resistance mutations in the Candida albicans drug target confer cross-resistance without intrinsic fitness cost.

Azole antifungals are the main drugs used to treat fungal infections. Amino acid substitutions in the drug target Erg11 (Cyp51) are a common resistance mechanism in pathogenic yeasts. How many and which mutations confer resistance is, however, largely unknown. Here we measure the impact of nearly 4,000 amino acid variants of Candida albicans Erg11 on the susceptibility to six clinical azoles. This was achieved by deep mutational scanning of CaErg11 expressed in Saccharomyces cerevisiae. We find that a large fraction of mutations lead to resistance (33%), most resistance mutations confer cross-resistance (88%) and only a handful of resistance mutations show a significant fitness cost (9%). Our results reveal that resistance to azoles can arise through a large set of mutations and this will probably lead to azole pan-resistance, with little evolutionary compromise. This resource will help inform treatment choices in clinical settings and guide the development of new drugs.

Crop protection practices and risks associated with human fungal infectious diseases: a One Health perspective

We review interactions between crop protection practices (developed to control plant pathogens and invertebrate pests) and human fungal infectious diseases. Unlike viral, bacterial and parasitic infections, fungal infections in humans are usually only superficial in healthy individuals, but can become invasive and pose serious risks to immunosuppressed individuals. Although their global impact is less than that of other infectious diseases, human fungal infections still pose serious public health issues. For instance, the use of synthetic agricultural fungicides, particularly the azole class, under conventional intensive, or efficiency improvement-based crop protection practices, is at risk as far as antimicrobial resistance is concerned, due to cases of cross-resistance to clinical azoles used to treat pulmonary aspergillosis, candidiasis and cryptococcocis. In this respect, the One Health approach, originally designed for other types of human pathogens, looks relevant for human pathogenic fungi. Additionally, some entomopathogenic fungi used as biocontrol products against crop pests in a substitution-based approach, may be potentially pathogenic to humans. Very few examples of redesign-based practices (i.e. Agroecological Crop Protection) emerged from our analysis on human fungal diseases. However, discontinuing agricultural azole fungicides (as practiced on organic farms, and which may to some extent be related to the redesign strategy) appears to be the best way to reduce selection pressure and hence the level of azole-resistant human pathogenic fungal strains in the environment.

P039 Cross-resistance to clinical and agricultural azoles among Aspergillus fumigatus strains isolated from humans and environment in Italy

Poster session 1, September 21, 2022, 12:30 PM - 1:30 PMObjectivesIn Italy, a prevalence of 16.9% of resistance to clinical azoles was observed among Aspergillus fumigatus isolates from an agricultural environment. This spread of azole-resistance is attributed to the widespread use of 14a-demethylase inhibitors (DMIs).The aims of the present study were to investigate: the DMIs resistance in Italian A. fumigatus strains of clinical and environmental origin, both susceptible and resistant to clinical azoles; the molecular mechanism of resistance in strains susceptible to clinical azoles but resistant to at least one of the tested DMIs; the in vitro DMI resistance induced by prolonged exposure to DMIs in susceptible clinical and environmental strains, and the molecular mechanism of resistance.MethodsA total of 54 A. fumigatus strains were selected: 23 susceptible to clinical azoles (CAS) and 31 resistant (CAR) with and without mutations in the CYP51A gene (TR34/L98H, F219I, G54R, G54E, D269Y, M220I, or F46Y/M172V/N248T/D255E/E427K). Antifungal susceptibility testing was performed for 8 DMIs (tebuconazole, epoxiconazole, difenoconazole, propiconazole, tetraconazole, flusilazole, fenbuconazole, and prochloraz) using broth microdilution method according to EUCAST and CLSI methods. Mutations in CYP51A, CYP51B, and HMG1 genes were investigated in CAS with DMI high MIC values. In vitro induction of resistance was performed using the 8 DMIs on 11 (6 clinical and 5 environmental) A. fumigatus strains susceptible both to clinical azoles and DMIs. A suspension of 106 conidia was inoculated on glucose-yeast extract-peptone agar plates containing different DMIs at different concentrations and incubated at 37°C for 72 h for six repeated passages.ResultsComparable results were obtained using EUCAST and CLSI methods.Resistance (MIC ≥16) to tetraconazole and fenbuconazole was observed in 100% of isolates, both CAR and CAS. On the contrary, a statistically significant difference in tebuconazole, epoxiconazole, difenoconazole, propiconazole, and flusilazole MICs between CAR strains and CAS strains was observed with higher geometric means (GM) in CAR (range 4.9-9.3 mg/L) than in CAS (1.5-2.7 mg/L) strains. Prochloraz showed the lowest GMs: 0.6 and 0.25 mg/L in CAR and CAS strains, respectively.A significant difference of the GMs for all the DMIs tested, except prochloraz, was observed between the isolates harboring a TR34/L98H or a M220I mutation (GM range 10.4-16 mg/L) and those with other CYP51A mutations (GM range 1-4.6 mg/L).In the CAS showing high DMI MICs, the absence of CYP51A mutations was confirmed, while a synonymous mutation P394P, was identified in CYP51B. No mutations in HMG1 gene were found.In the induction tests, the prolonged exposure to DMIs showed an induced phenotypic resistance of 100% (11/11 isolates) for epoxiconazole, of 72.7% (8/11) for propiconazole, of 54% (6/11) for tebuconazole and difenoconazole, and of 9.1% (1/11) for prochloraz.Molecular analysis to understand if the phenotypic resistance corresponds to induced mutations in CYP51A, CYP51B, and HMG1 genes is in progress.ConclusionsPreliminary results confirm cross-resistance between clinical azoles and DMIs, with MIC differences between CAR and CAS and between strains with different mutations in the CYP51A gene. Furthermore, the ability of DMIs to induce resistance in vitro was highlighted.

Evidence for the agricultural origin of resistance to multiple antimicrobials in Aspergillus fumigatus, a fungal pathogen of humans.

Pathogen resistance to clinical antimicrobial agents is an urgent problem. The fungus Aspergillus fumigatus causes 300,000 life-threatening infections in susceptible humans annually. Azoles, which are widely used in both clinical and agricultural settings, are currently the most effective treatment, but resistance to clinical azoles is emerging worldwide. Here, we report the isolation and analysis of azole-sensitive and azole-resistant A. fumigatus from agricultural environments in the southeastern United States (USA) and show that the USA pan-azole-resistant isolates form a clade with pan-azole-resistant isolates from the United Kingdom, the Netherlands, and India. We show that several pan-azole-resistant isolates from agricultural settings in the USA and India also carry alleles with mutations conferring resistance to agricultural fungicides from the benzimidazole (MBC) and quinone outside inhibitor (QoI) classes. We further show that pan-azole-resistant A. fumigatus isolates from patients in clinical settings in the USA, India, and the Netherlands also carry alleles conferring resistance to MBC and QoI agricultural fungicides. The presence of markers for resistance to agricultural-use fungicides in clinical A. fumigatus isolates is strong evidence for an agricultural origin of pan-azole resistance in patients. The presence of multiple fungicide-resistance alleles in agricultural and clinical isolates further suggests that the unique genetics of the pan-azole-resistant clade enables the evolution and/or persistence of antimicrobial resistance mutations leading to the establishment of multifungicide-resistant isolates.

An expanded agar-based screening method for azole-resistant Aspergillus fumigatus.

Antifungal susceptibility testing is an essential tool for guiding antifungal therapy. Reference methods are complex and usually only available in specialised laboratories. We have designed an expanded agar-based screening method for the detection of azole-resistant Aspergillus fumigatus isolates. Normally, identification of resistance mechanisms is obtained only after sequencing the cyp51A gene and promoter. However, our screening method provides azole resistance detection and presumptive resistance mechanisms identification. A previous agar-based method consisting of four wells containing voriconazole, itraconazole, posaconazole and a growth control, detected azole resistance to clinical azoles. Here, we have modified the concentrations of voriconazole and posaconazole to adapt to the updated EUCAST breakpoints against A.fumigatus. We have also expanded the method to include environmental azoles to assess azole resistance and the azole resistance mechanism involved. We used a collection of A.fumigatus including 54 azole-resistant isolates with Cyp51A modifications (G54, M220, G448S, TR53 , TR34 /L98H, TR46 /Y121F/T289A, TR34 /L98H/S297T/F495I), and 50 azole susceptible isolates with wild-type Cyp51A. The screening method detects azole-resistant A.fumigatus isolates when there is growth in any of the azole-containing wells after 48h. The growth pattern in the seven azoles tested helps determine the underlying azole resistance mechanism. This approach is designed for surveillance screening of A.fumigatus azole-resistant isolates and can be useful for the clinical management of patients prior to antifungal susceptibility testing confirmation.

Are Point Mutations in HMG-CoA Reductases (Hmg1 and Hmg2) a Step towards Azole Resistance in Aspergillus fumigatus?

Invasive aspergillosis, mainly caused by Aspergillus fumigatus, can lead to severe clinical outcomes in immunocompromised individuals. Antifungal treatment, based on the use of azoles, is crucial to increase survival rates. However, the recent emergence of azole-resistant A. fumigatus isolates is affecting the efficacy of the clinical therapy and lowering the success rate of azole strategies against aspergillosis. Azole resistance mechanisms described to date are mainly associated with mutations in the azole target gene cyp51A that entail structural changes in Cyp51A or overexpression of the gene. However, strains lacking cyp51A modifications but resistant to clinical azoles have recently been detected. Some genes have been proposed as new players in azole resistance. In this study, the gene hmg1, recently related to azole resistance, and its paralogue hmg2 were studied in a collection of fifteen azole-resistant strains without cyp51A modifications. Both genes encode HMG-CoA reductases and are involved in the ergosterol biosynthesis. Several mutations located in the sterol sensing domain (SSD) of Hmg1 (D242Y, G307D/S, P309L, K319Q, Y368H, F390L and I412T) and Hmg2 (I235S, V303A, I312S, I360F and V397C) were detected. The role of these mutations in conferring azole resistance is discussed in this work.

1598. Clinical implications of azole-resistant vs. azole-susceptible invasive aspergillosis in hematological malignancy (CLARITY) – a multicenter study

BackgroundAdvances in the survival of patients with invasive aspergillosis (IA) are jeopardized by the emergence of azole resistance in Aspergillus fumigatus, which has been associated with high probability of azole treatment failure. The clinical implications of azole-resistant IA compared to azole-susceptible IA remain unclear. Thus, we seek to describe the epidemiology and to determine the efficacy of antifungal therapy in patients with documented azole-resistant IA compared to azole-susceptible IA in patients with hematological malignancy.MethodsFor proven and probable IA (EORTC/MSG 2019) caused by A. fumigatus in patients with hematological malignancies retrospective data were documented, comprising demographics, diagnosis, treatment, response, and outcome. Sites provided susceptibility results or respective isolates for analysis in a central laboratory.ResultsSites in 16 countries worldwide enrolled 187 cases diagnosed with IA between 2010 and 2019; 31 (16.6%) were resistant to at least one of the clinical azoles. Fungal isolates were available from 42 cases. A mixed fungal infection was reported for 32 patients (17.1%), most were related to non-fumigatus Aspergillus and non-Aspergillus molds (n=22, 69%). Most patients were male (66.8%) and overall the majority of patients were in the age groups between 50 and 89 years (71%). Amphotericin B was used for treatment in 24 (77%) patients with azole-resistant IA, compared to 76 (49%) in the azole-susceptible group (lipid-based formulation in 98%); only five (16%) patients with azole-resistant IA were treated with an azole alone vs. 57 (36%) of those with azole-susceptible IA. Overall, all-cause mortality rate was higher for patients with azole-resistant compared to azole-susceptible IA (74.2% vs. 53.8%, log rank P=0.004), the 8 patients with an azole-resistant IA treated in the intensive care unit died within 1 month (Figure 1). Details on underlying disease and survival are given in Table 1.Table 1. Underlying hematological malignancy and clinical outcome of patients with azole-resistant and azole-susceptible invasive aspergillosis Figure 1. Intensive care unit 1-year survival probability for patients with azole-resistant and azole-susceptible invasive aspergillosis ConclusionAzole-resistance in IA is associated with worse outcome, especially in critically ill patients. Susceptibility testing should be considered in patients with a suspected azole-resistant IA to support treatment decisions.Disclosures Danila Seidel, PhD, Basilea (Other Financial or Material Support, travel grant) Oliver Cornely, Prof., Actelion (Grant/Research Support)Actelion (Other Financial or Material Support, Personal fees)Al Jazeera Pharmaceuticals (Consultant)Allecra Therapeutics (Other Financial or Material Support, Personal fees)Amplyx (Other Financial or Material Support, Personal fees)Amplyx (Grant/Research Support)Astellas (Grant/Research Support)Astellas (Other Financial or Material Support, Personal fees)Basilea (Other Financial or Material Support, Personal fees)Basilea (Grant/Research Support)Biosys UK Limited (Other Financial or Material Support, Personal fees)Cidara (Other Financial or Material Support, Personal fees)Cidara (Grant/Research Support)Da Volterra (Grant/Research Support)Da Volterra (Other Financial or Material Support, Personal fees)Entasis (Other Financial or Material Support, Personal fees)F2G (Other Financial or Material Support)F2G (Grant/Research Support)Gilead (Grant/Research Support)Gilead (Other Financial or Material Support, Personal fees)Grupo Biotoscana (Other Financial or Material Support, Personal fees)Janssen Pharmaceuticals (Grant/Research Support)Matinas (Other Financial or Material Support, Personal fees)Medicines Company (Grant/Research Support)MedPace (Grant/Research Support)MedPace (Other Financial or Material Support, Personal fees)Melinta Therapeutics (Grant/Research Support)Menarini Ricerche (Other Financial or Material Support, Personal fees)Merck/MSD (Other Financial or Material Support, Personal fees)Merck/MSD (Grant/Research Support)Mylan Pharmaceuticals (Consultant)Nabriva Therapeutics (Other Financial or Material Support, Personal fees)Octapharma (Other Financial or Material Support, Personal fees)Paratek Pharmaceuticals (Other Financial or Material Support, Personal fees)Pfizer (Other Financial or Material Support, Personal fees)Pfizer (Grant/Research Support)PSI (Other Financial or Material Support, Personal fees)Rempex (Other Financial or Material Support, Personal fees)Roche Diagnostics (Other Financial or Material Support, Personal fees)Scynexis (Other Financial or Material Support, Personal fees)Scynexis (Grant/Research Support)Seres Therapeutics (Other Financial or Material Support, Personal fees)Tetraphase (Other Financial or Material Support, Personal fees) Philipp Koehler, MD, Akademie für Infektionsmedizin e.V., (Other Financial or Material Support, Personal fees)Astellas Pharma GmbH (Other Financial or Material Support, Personal fees)Cologne Excellence Cluster on Cellular Stress Responses in Aging-Associated Diseases, University of Cologne, Cologne, Germany (Other Financial or Material Support, Other)Gilead Sciences GmbH (Other Financial or Material Support, Personal fees)GPR Academy Ruesselsheim (Speaker’s Bureau)Miltenyi Biotec GmbH (Other Financial or Material Support, Non-financial support)MSD Sharp & Dohme GmbH (Other Financial or Material Support, Personal fees)Noxxon N.V. (Speaker’s Bureau)University Hospital, LMU Munich (Other Financial or Material Support, Personal fees) Katrien Lagrou, n/a, FUJIFILM WAKO (Speaker’s Bureau)Gilead (Consultant, Speaker’s Bureau)MSD (Consultant, Speaker’s Bureau, Other Financial or Material Support, travel grant)Pfizer (Speaker’s Bureau, travel grant)SMB Laboratoires Brussels (Consultant) Zdenek Racil, n/a, Astellas (Grant/Research Support, Speaker’s Bureau, travel grant) Blandine Rammaert, n/a, Gilead (Speaker’s Bureau, Other Financial or Material Support, travel grant)Merck/MSD (Speaker’s Bureau)Pfizer (Other Financial or Material Support, travel grant) Nikolay Klimko, n/a, Astellas (Speaker’s Bureau)Gilead (Speaker’s Bureau)Merck/MSD (Speaker’s Bureau)Pfizer (Speaker’s Bureau) Sung-Yeon Cho, MD, Gilead (Grant/Research Support, Speaker’s Bureau)Merck Sharp & Dohme (Grant/Research Support, Speaker’s Bureau)Pfizer (Grant/Research Support, Speaker’s Bureau)

A Cyp51B Mutation Contributes to Azole Resistance in Aspergillus fumigatus.

The emergence and spread of Aspergillus fumigatus azole resistance has been acknowledged worldwide. The main problem of azole resistance is the limited therapeutic options for patients suffering aspergillosis. Azole resistance mechanisms have been mostly linked to the enzyme Cyp51A, a target of azole drugs, with a wide variety of modifications responsible for the different resistance mechanisms described to date. However, there are increasing reports of A. fumigatus strains showing azole resistance without Cyp51A modifications, and thus, novel resistance mechanisms are being explored. Here, we characterized two isogenic A. fumigatus clinical strains isolated two years apart from the same patient. Both strains were resistant to clinical azoles but showed different azole resistance mechanisms. One strain (CM8940) harbored a previously described G54A mutation in Cyp51A while the other strain (CM9640) had a novel G457S mutation in Cyp51B, the other target of azoles. In addition, this second strain had a F390L mutation in Hmg1. CM9640 showed higher levels of gene expression of cyp51A, cyp51B and hmg1 than the CM8940 strain. The role of the novel mutation found in Cyp51B together with the contribution of a mutation in Hmg1 in azole resistance is discussed.

Point Mutations in the 14-α Sterol Demethylase Cyp51A or Cyp51C Could Contribute to Azole Resistance in Aspergillus flavus.

Infections caused by Aspergillus species are being increasingly reported. Aspergillus flavus is the second most common species within this genus causing invasive infections in humans, and isolates showing azole resistance have been recently described. A. flavus has three cyp51-related genes (cyp51A, cyp51B, and cyp51C) encoding 14-α sterol demethylase-like enzymes which are the target of azole drugs. In order to study triazole drug resistance in A. flavus, three strains showing reduced azole susceptibility and 17 azole susceptible isolates were compared. The three cyp51-related genes were amplified and sequenced. A comparison of the deduced Cyp51A, Cyp51B, and Cyp51C protein sequences with other protein sequences from orthologous genes in different filamentous fungi led to a protein identity that ranged from 50% to 80%. Cyp51A and Cyp51C presented several synonymous and non-synonymous point mutations among both susceptible and non-susceptible strains. However, two amino acid mutations were present only in two resistant isolates: one strain harbored a P214L substitution in Cyp51A, and another a H349R in Cyp51C that also showed an increase of cyp51A and cyp51C gene expression compared to the susceptible strain ATCC2004304. Isolates that showed reduced in vitro susceptibility to clinical azoles exhibited a different susceptibility profile to demethylation inhibitors (DMIs). Although P214L substitution might contribute to azole resistance, the role of H349R substitution together with changes in gene expression remains unclear.

From the environment to the host: How non-azole agrochemical exposure affects the antifungal susceptibility and virulence of Cryptococcus gattii

Agrochemicals such as the non-azoles, used to improve crop productivity, poses severe undesirable effects on the environment and human health. In addition, they induce cross-resistance (CR) with clinical drugs in pathogenic fungi. However, till date emphasis has been given to the role of azoles on the induction of CR. Herein, we analyzed the effect of a non-azole agrochemical, pyraclostrobin (PCT), on the antifungal susceptibility and virulence of the human and animal pathogens Cryptococcus gattii and C. neoformans. We determined the minimum inhibitory concentration (MIC) of fluconazole (FLC), itraconazole, ravuconazole, amphotericin B, and PCT on colonies: (i) that were not exposed to PCT (non-adapted-NA-cultures), (ii) were exposed at the maximum concentration of PCT (adapted-A-cultures) and (iii) the adapted colonies after cultivation 10 times in PCT-free media (10 passages-10p–cultures). Our results showed that exposure to PCT induced both temporary and permanent CR to clinical azoles in a temperature-dependent manner. With the objective to understand the mechanism of induction of CR through non-azoles, the transcriptomes of NA and 10p cells from C. gattii R265 were analyzed. The transcriptomic analysis showed that expression of the efflux-pump genes (AFR1 and MDR1) and PCT target was higher in resistant 10p cells than that in NA. Moreover, the virulence of 10p cells was reduced as compared to NA cells in mice, as observed by the differential gene expression analysis of genes related to ion-metabolism. Additionally, we observed that FLC could not increase the survival rate of mice infected with 10p cells, confirming the occurrence of permanent CR in vivo. The findings of the present study demonstrate that the non-azole agrochemical PCT can induce permanent CR to clinical antifungals through increased expression of efflux pump genes in resistant cells and that such phenomenon also manifests in vivo.

Exposure of Candida parapsilosis complex to agricultural azoles: An overview of the role of environmental determinants for the development of resistance

This work investigated the phenotypic behavior of Candida parapsilosis species complex in response to exposure to agricultural azoles and fluconazole. Three fluconazole-susceptible strains of C. parapsilosis sensu stricto, C. orthopsilosis and C. metapsilosis were used. Initial minimum inhibitory concentrations (iMICs) for agricultural and clinical azoles were determined by broth microdilution. Then, the strains were exposed to tebuconazole, tetraconazole and fluconazole for 15 days, at concentrations that were two-folded daily, starting at one-eighth the iMIC (iMIC/8) up to 64 times iMIC (64xiMIC). After 15-day-exposure, antifungal susceptibility, biofilm formation, CDR, MDR and ERG expression were evaluated. The three cryptic species developed tolerance to the antifungals they were exposed and presented reduction (P < 0.05) in fluconazole susceptibility. In addition, C. parapsilosis sensu stricto and C. metapsilosis also presented reduced susceptibility to voriconazole, after fluconazole exposure. Azole exposure decreased (P < 0.05) biofilm production by C. parapsilosis sensu stricto and C. orthopsilosis and increased (P < 0.05) the expression of ERG11 in all tested strains. The results show that exposure to agricultural azoles and fluconazole induces changes in the phenotypic behavior and gene expression by the three cryptic species of C. parapsilosis complex, highlighting the importance of environmental determinants for the development of antifungal resistance.

CYP51 as drug targets for fungi and protozoan parasites: past, present and future.

The efficiency of treatment of human infections with the unicellular eukaryotic pathogens such as fungi and protozoa remains deeply unsatisfactory. For example, the mortality rates from nosocomial fungemia in critically ill, immunosuppressed or post-cancer patients often exceed 50%. A set of six systemic clinical azoles [sterol 14α-demethylase (CYP51) inhibitors] represents the first-line antifungal treatment. All these drugs were discovered empirically, by monitoring their effects on fungal cell growth, though it had been proven that they kill fungal cells by blocking the biosynthesis of ergosterol in fungi at the stage of 14α-demethylation of the sterol nucleus. This review briefs the history of antifungal azoles, outlines the situation with the current clinical azole-based drugs, describes the attempts of their repurposing for treatment of human infections with the protozoan parasites that, similar to fungi, also produce endogenous sterols, and discusses the most recently acquired knowledge on the CYP51 structure/function and inhibition. It is our belief that this information should be helpful in shifting from the traditional phenotypic screening to the actual target-driven drug discovery paradigm, which will rationalize and substantially accelerate the development of new, more efficient and pathogen-oriented CYP51 inhibitors.

Environmental Triazole Induces Cross-Resistance to Clinical Drugs and Affects Morphophysiology and Virulence of Cryptococcus gattii and C. neoformans.

Cryptococcus gattii and Cryptococcus neoformans are environmental fungi that cause cryptococcosis, which is usually treated with amphotericin B and fluconazole. However, therapeutic failure is increasing because of the emergence of resistant strains. Because these species are constantly isolated from vegetal materials and the usage of agrochemicals is growing, we postulate that pesticides could be responsible for the altered susceptibility of these fungi to clinical drugs. Therefore, we evaluated the influence of the pesticide tebuconazole on the susceptibility to clinical drugs, morphophysiology, and virulence of C. gattii and C. neoformans strains. The results showed that tebuconazole exposure caused in vitro cross-resistance (CR) between the agrochemical and clinical azoles (fluconazole, itraconazole, and ravuconazole) but not with amphotericin B. In some strains, CR was observed even after the exposure ceased. Further, tebuconazole exposure changed the morphology, including formation of pseudohyphae in C. neoformans H99, and the surface charge of the cells. Although the virulence of both species previously exposed to tebuconazole was decreased in mice, the tebuconazole-exposed colonies recovered from the lungs were more resistant to azole drugs than the nonexposed cells. This in vivo CR was confirmed when fluconazole was not able to reduce the fungal burden in the lungs of mice. The tolerance to azoles could be due to increased expression of the ERG11 gene in both species and of efflux pump genes (AFR1 and MDR1) in C. neoformans Our study data support the idea that agrochemical usage can significantly affect human pathogens present in the environment by affecting their resistance to clinical drugs.

Notable Increasing Trend in Azole Non-susceptible Candida tropicalis Causing Invasive Candidiasis in China (August 2009 to July 2014): Molecular Epidemiology and Clinical Azole Consumption.

Objectives: To report the notable increasing trends of C. tropicalis antifungal resistance in the past 5 years, and explore molecular epidemiology, and the relationship between clinical azoles consumption and increased resistance rate.Methods: Between August 2009 and July 2014, 507 non-duplicated C. tropicalis isolates causing invasive candidiasis were collected from 10 hospitals in China. The in vitro antifungal susceptibility of nine common agents was determined by Sensititre YeastOne™ using current available species-specific clinical breakpoint (CBPs) or epidemiological cut-off values (ECVs). A high discriminatory three-locus (ctm1, ctm3, and ctm24) microsatellite scheme was used for typing of all isolates collected. Clinical consumption of fluconazole and voriconazole was obtained and the Defined Daily Dose measurement units were assigned to the data.Results: Overall, 23.1 and 20.7% of isolates were non-susceptible to fluconazole and voriconazole, respectively. And over 5 years, the non-susceptible rate of C. tropicalis isolates to fluconazole and voriconazole continuously increased from 11.2 to 42.7% for fluconazole (P < 0.001), and from 10.4 to 39.1% for voriconazole (P < 0.001). Four genotype clusters were observed to be associated with fluconazole non-susceptible phenotype. However, the increase in azole non-susceptible rate didn't correlate with clinical azole consumption.Conclusions: The rapid emergence of azole resistant C. tropicalis strains in China is worrying, and continuous surveillance is warranted and if the trend persists, empirical therapeutic strategies for C. tropicalis invasive infections should be modified.

Cross-resistance to fluconazole induced by exposure to the agricultural azole tetraconazole: an environmental resistance school?

This study aimed to investigate the influence of tetraconazole and malathion, both used in agricultural activities, on resistance to fluconazole, itraconazole and voriconazole in Candida parapsilosis ATCC 22019. The susceptibility to tetraconazole, malathion, fluconazole, itraconazole and voriconazole, through broth microdilution. Then, 12 independent replicates, were separated and exposed to four treatment groups, each one containing three replicates: G1: tetraconazole; G2: malathion; G3: fluconazole (positive control); G4: negative control. Replicates from G1, G2 and G3, were exposed to weekly increasing concentrations of tetraconazole, malathion and fluconazole, respectively, ranging from MIC/2 to 32 × MIC, throughout 7 weeks. The exposure to tetraconazole, but not malathion, decreased susceptibility to clinical azoles, especially fluconazole. The tetraconazole-induced fluconazole resistance is partially mediated by the increased activity of ATP-dependent efflux pumps, considering the increase in antifungal susceptibility after the addition of the efflux pump inhibitor, promethazine, and the increase in rhodamine 6G efflux and CDR gene expression in the G1 replicates. Moreover, MDR expression was only detected in G1 and G3 replicates, suggesting that MDR pumps are also involved in tetraconazole-induced fluconazole resistance. It is noteworthy that tetraconazole and fluconazole-treated replicates behaved similarly, therefore, resistance to azoles of clinical use may be a consequence of using azoles in farming activities.

High prevalence of azole resistance in Aspergillus fumigatus isolates from high-risk patients.

Aspergillus fumigatus is the leading cause of invasive aspergillosis. Adequate treatment is complicated by an increase in azole resistance. Here, the incidence of voriconazole, posaconazole and itraconazole resistance in clinical isolates from high-risk patients from either the haematology ward or the ICU of the University Medical Center Utrecht in the period 2011-13 is analysed. Putative clonality of resistant strains was tested through cyp51A and microsatellite typing. Primary A. fumigatus isolates from 105 patients were collected by an unbiased routine diagnostic-driven approach and phenotypically tested for azole susceptibility. Of the 105 isolates, 5 were from patients with a proven invasive A. fumigatus infection, 48 were from patients with a probable invasive A. fumigatus infection and 52 were from patients with non-invasive infections. Real-time PCR and cyp51A gene and strain typing were performed. Twenty-one out of 105 (20.0%) isolates were resistant to at least one of the three clinical azoles and 17/105 (16.2%) isolates were resistant (MIC >2 mg/L) to voriconazole, the empirical drug of choice for treatment of aspergillosis. There was a striking difference in the prevalence of triazole resistance, with 15.9% resistant isolates (25.0% in proven/probable patients) in the haematology population and 4.5% (10% in proven/probable) in the ICU. While the majority of isolates with elevated MICs of voriconazole were cyp51A related (17/23), both microsatellite and cyp51A sequence typing argue against clonal spread of resistant strains. This study reveals a high incidence of voriconazole resistance (16.2%) in A. fumigatus in high-risk patients. Our data stress the need for laboratory detection of azole resistance prior to treatment.

Environmental azole fungicide, prochloraz, can induce cross-resistance to medical triazoles in Candida glabrata.

Acquisition of azole resistance by clinically relevant yeasts in nature may result in a significant, yet undetermined, impact in human health. The main goal of this study was to assess the development of cross-resistance between agricultural and clinical azoles by Candida spp. An in vitro induction assay was performed, for a period of 90 days, with prochloraz (PCZ) - an agricultural antifungal. Afterward, the induced molecular resistance mechanisms were unveiled. MIC value of PCZ increased significantly in all Candida spp. isolates. However, only C.glabrata developed cross-resistance to fluconazole and posaconazole. The increased MIC values were stable. Candida glabrata azole resistance acquisition triggered by PCZ exposure involved the upregulation of the ATP binding cassette multidrug transporter genes and the transcription factor, PDR1. Single mutation previously implicated in azole resistance was found in PDR1 while ERG11 showed several synonymous single nucleotide polymorphisms. These results might explain why C.glabrata is so commonly less susceptible to clinical azoles, suggesting that its exposure to agricultural azole antifungals may be associated to the emergence of cross-resistance. Such studies forward potential explanations for the worldwide increasing clinical prevalence of C.glabrata and the associated worse prognosis of an infection by this species.

Development of cross-resistance by Aspergillus fumigatus to clinical azoles following exposure to prochloraz, an agricultural azole.

BackgroundThe purpose of this study was to unveil whether azole antifungals used in agriculture, similar to the clinical azoles used in humans, can evoke resistance among relevant human pathogens like Aspergillus fumigatus, an ubiquitous agent in nature. Additionally, cross-resistance with clinical azoles was investigated. Antifungal susceptibility testing of environmental and clinical isolates of A. fumigatus was performed according to the CLSI M38-A2 protocol. In vitro induction assays were conducted involving daily incubation of susceptible A. fumigatus isolates, at 35°C and 180 rpm, in fresh GYEP broth medium supplemented with Prochloraz (PCZ), a potent agricultural antifungal, for a period of 30 days. Minimal inhibitory concentrations (MIC) of PCZ and clinical azoles were monitored every ten days. In order to assess the stability of the developed MIC, the strains were afterwards sub-cultured for an additional 30 days in the absence of antifungal. Along the in vitro induction process, microscopic and macroscopic cultural observations were registered.ResultsMIC of PCZ increased 256 times after the initial exposure; cross-resistance to all tested clinical azoles was observed. The new MIC value of agricultural and of clinical azoles maintained stable in the absence of the selective PCZ pressure. PCZ exposure was also associated to morphological colony changes: macroscopically the colonies became mostly white, losing the typical pigmentation; microscopic examination revealed the absence of conidiation.ConclusionsPCZ exposure induced Aspergillus fumigatus morphological changes and an evident increase of MIC value to PCZ as well as the development of cross-resistance with posaconazole, itraconazole and voriconazole.

CYP51 structures and structure-based development of novel, pathogen-specific inhibitory scaffolds

CYP51 (sterol 14α-demethylase) is a cytochrome P450 enzyme essential for sterol biosynthesis and the primary target for clinical and agricultural antifungal azoles. The azoles that are currently in clinical use for systemic fungal infections represent modifications of two basic scaffolds, ketoconazole and fluconazole, all of them being selected based on their antiparasitic activity in cellular experiments. By studying direct inhibition of CYP51 activity across phylogeny including human pathogens Trypanosoma brucei, Trypanosoma cruzi and Leishmania infantum, we identified three novel protozoa-specific inhibitory scaffolds, their inhibitory potency correlating well with antiprotozoan activity. VNI scaffold (carboxamide containing β-phenyl-imidazoles) is the most promising among them: killing T. cruzi amastigotes at low nanomolar concentration, it is also easy to synthesize and nontoxic. Oral administration of VNI (up to 400mg/kg) neither leads to mortality nor reveals significant side effects up to 48h post treatment using an experimental mouse model of acute toxicity. Trypanosomatidae CYP51 crystal structures determined in the ligand-free state and complexed with several azole inhibitors as well as a substrate analog revealed high rigidity of the CYP51 substrate binding cavity, which must be essential for the enzyme strict substrate specificity and functional conservation. Explaining profound potency of the VNI inhibitory scaffold, the structures also outline guidelines for its further development. First steps of the VNI scaffold optimization have been undertaken; the results presented here support the notion that CYP51 structure-based rational design of more efficient, pathogen-specific inhibitors represents a highly promising direction.

Structural complex of sterol 14α-demethylase (CYP51) with 14α-methylenecyclopropyl-Δ7-24, 25-dihydrolanosterol

Sterol 14α-demethylase (CYP51) that catalyzes the removal of the 14α-methyl group from the sterol nucleus is an essential enzyme in sterol biosynthesis, a primary target for clinical and agricultural antifungal azoles and an emerging target for antitrypanosomal chemotherapy. Here, we present the crystal structure of Trypanosoma (T) brucei CYP51 in complex with the substrate analog 14α-methylenecyclopropyl-Δ7-24,25-dihydrolanosterol (MCP). This sterol binds tightly to all protozoan CYP51s and acts as a competitive inhibitor of F105-containing (plant-like) T. brucei and Leishmania (L) infantum orthologs, but it has a much stronger, mechanism-based inhibitory effect on I105-containing (animal/fungi-like) T. cruzi CYP51. Depicting substrate orientation in the conserved CYP51 binding cavity, the complex specifies the roles of the contact amino acid residues and sheds new light on CYP51 substrate specificity. It also provides an explanation for the effect of MCP on T. cruzi CYP51. Comparison with the ligand-free and azole-bound structures supports the notion of structural rigidity as the characteristic feature of the CYP51 substrate binding cavity, confirming the enzyme as an excellent candidate for structure-directed design of new drugs, including mechanism-based substrate analog inhibitors.