Molecular Mechanisms Of Azole Resistance Research Articles

Mechanism of azole resistance in Candida vulturna, an emerging multidrug resistant pathogen related with Candida haeumulonii and Candida auris.

Candida vulturna is an emerging pathogen belonging to the Metshnikowiaceae family together with Candida auris and Candida haemulonii species complex. Some strains of this species were reported to be resistant to several antifungal agents. This study aims to address identification difficulties, evaluate antiungal susceptibilities and explore the molecular mechanisms of azole resistance of Candida vulturna. We studied five C. vulturna clinical strains isolated in three Colombian cities. Identification was performed by phenotypical, proteomic and molecular methods. Antifungal susceptibility testing was performed following CLSI protocol. Its ERG11 genes were sequenced and a substitution was encountered in azole resistant isolates. To confirm the role of this substitution in the resistance phenotype, Saccharomyces cerevisiae strains with a chimeric ERG11 gene were created. Discrepancies in identification methods are highlighted. Sequencing confirmed the identification as C. vulturna. Antifungal susceptibility varied among strains, with four strains exhibiting reduced susceptibility to azoles and amphotericin B. ERG11 sequencing showed a point mutation (producing a P135S substitution) that was associated with the azole-resistant phenotype. This study contributes to the understanding of C. vulturna's identification challenges, its susceptibility patterns, and sheds light on its molecular mechanisms of azole resistance.

Molecular mechanisms of azole resistance in Candida glabrata isolated from oropharyngeal candidiasis in head and neck cancer patients

ObjectiveThe aim of the current work was to assess the molecular mechanisms of fluconazole-resistant Candida glabrata strains isolated from oropharyngeal candidiasis (OPC) in head and neck patients, as well as evaluation of virulence factors. DesignAntifungal susceptibility pattern of sixty six clinical isolates of C. glabrata were evaluated by broth-microdilution method. The expression of ERG11, CDR1, CDR2, PDR1 genes as well as ERG11 gene capable of possible mutations was also detected in 21 fluconazol-resistant C. glabrata isolates. Phospholipase and proteinase activity of these isolates was estimated, too. The correlation between the virulence factors, antifungal susceptibility patterns and cancer type was also analyzed. ResultsSeven synonymous and four non-synonymous mutations were found in 21 fluconazole-resistant C. glabrata isolates; subsequently, four amino acid substitutions including H257P, Q47H, S487Y and I285N were then reported for the first time. High expression of CDR1 and PDR1 in related to other gene findings were tested in these isolates. Additionally, there was no significant difference between stage of cancer and MIC of all antimicrobial drugs. Significant differences between MIC of fluconazole, voriconazole and cancer types were also, found. The proteinase activity (92.4%) was higher than phospholipase activity in the isolates. Further, no significant difference between proteinase (rs: 0.003), phospholipase (rs: −0.107) activity and fluconazole MICs was observed. ConclusionC. glabrata isolated from OPC in head and neck patients represented high capacities for proteolytic enzymes activity and high mRNA level of CDR1 and PDR1 gene and ERG11 mutations play an important role in azole drug resistance.

Azole resistance in Candida auris: mechanisms and combinatorial therapy.

Multidrug resistance Candida auris is a dangerous fungal pathogen that is emerging at an alarming rate and posing serious threats to public health. C. auris is associated with nosocomial infections that cause invasive candidiasis in immunocompromised patients. Several antifungal drugs with distinct mechanisms of action are clinically approved for the treatment of fungal infections. The high rates of intrinsic and acquired drug resistance, particularly to azoles, reported in characterized clinical isolates of C. auris make treatment extremely problematic. In systemic infections, azoles are the first-line treatment for most Candida species; however, the increasing use of drugs results in the frequent emergence of drug resistance. More than 90% of the clinical isolates of C. auris is shown to be highly resistant to azole drugs especially fluconazole, with some strains (types) resistant to all three classes of commonly used antifungals. This presents a huge challenge for researchers in terms of completely understanding the molecular mechanism of azole resistance to develop more efficient drugs. Due to the scarcity of C. auris therapeutic alternatives, the development of successful drug combinations provides an alternative for clinical therapy. Taking advantage of various action mechanisms, such drugs in combination with azole are likely to have synergistic effects, improving treatment efficacy and overcoming C. auris azole drug resistance. In this review, we outline the current state of understanding about the mechanisms of azole resistance mainly fluconazole, and the current advancement in therapeutic approaches such as drug combinations toward C. auris infections.

Antifungal drug susceptibility profiles and molecular mechanisms of azole resistance in Candida blood stream isolates

PurposeThe purpose of this study was to determine the activity of fluconazole, voriconazole, posaconazole, amphotericin B, micafungin and caspofungin against Candida blood stream isolates and to investigate the molecular mechanisms of azole resistance in fluconazole resistant isolates. MethodsThe in vitro susceptibilities of Candida isolates to fluconazole, voriconazole, posaconazole, amphotericin B, micafungin and caspofungin were tested by E-test ERG11, CDR1, CDR2 and MDR1 genes expression of fluconazole resistant, fluconazole (S-DD) and fluconazole intermediate resistant isolates were investigated by quantitative real-time reverse transcriptase polymerase chain reaction (qRT-PCR). ResultsC. albicans (41%) was the most frequently isolated fungal species from blood stream infections followed by C. parapsilosis (22%). All C. albicans isolates except one and all C. tropicalis isolates were found to be susceptible to fluconazole. Overall, 21% of C. glabrata isolates were resistant to fluconazole. None of the Candida isolates were found to be resistant to caspofungin except 2 ​C. glabrata isolates. Overexpression of ERG11 and CDR1 genes were detected in all fluconazole S-DD and fluconazole resistant C. glabrata isolates, while CDR2 overexpression was observed in 91% fluconazole S-DD and 67 of % fluconazole resistant C.glabrata isolates. The overexpression of MDR1, ERG11 and CDR1 genes were found 100%, 80% and 80%, respectively, in fluconazole resistant C. parapsilosis isolates. ConclusionMost of the Candida isolates were susceptible to posaconazole and caspofungin. Our data also highlighted that overexpression of efflux pump genes major cause of azole resistance.

S5.1d Mechanisms of azole antifungal resistance in clinical isolates of Candida tropicalis

S5.1 Antifungal resistance, September 22, 2022, 3:00 PM - 4:30 PMObjectivesIn tropical countries, the azole resistance in Candida tropicalis is on the rise. There are limited studies available regarding the azole resistance mechanisms in C. tropicalis. This study was designed to understand the molecular mechanisms of azole resistance in C. tropicalis by using genetic and bioinformatics approaches.MethodsA total of 32 azole-resistant (R) and 10 azole-susceptible (S) clinical isolates of C. tropicalis were included in this study. All the isolates were subjected to complete gene sequencing of azole target genes including ERG11 to analyze the mutations which could lead the azole resistance. Four fragments were amplified, sequenced, and aligned to get full-length ERG11 gene. Inducible expression analysis of 17 other genes potentially associated with azole resistance was also evaluated. Homology modeling and molecular docking analysis were performed to study the effect of amino acid alterations in mediating azole resistance.ResultsOf the 32 resistant isolates, 12 (37.5%) showed A395T and C461T mutations in the ERG11 gene. The mean overexpression of CDR1, CDR3, TAC1, ERG1, ERG2, ERG3, ERG11, UPC2, and MKC1 in resistant isolates without mutation (R-WTM) was significantly higher (P <.05) than those with mutation (R-WM) and the sensitive isolates (3.2-11 vs. 0.2-2.5, and 0.3-2.2 folds, respectively). Although the R-WTM and R-WM had higher (P <.05) CDR2 and MRR1 expression compared to S isolates, noticeable variation was not seen among the other genes. Protein homology modeling and molecular docking revealed that the mutations in the ERG11 gene were responsible for structural alteration and low binding efficiency between ERG11p and ligands. Isolates with ERG11 mutations also presented A220C in ERG1 and together T503C, G751A mutations in UPC2.ConclusionsNonsynonymous mutations in the ERG11 gene and coordinated overexpression of various genes including different transporters, ergosterol biosynthesis pathway, transcription factors, and stress-responsive genes are associated with azole resistance in clinical isolates of C. tropicalis.

P019 A 5-year study on prevalence and molecular determinants of fluconazole -resistance in C. parapsilosis spp. complex

Post Graduate Institute of Medical Education and Research, Chandigarh, IndiaPoster session 1, September 21, 2022, 12:30 PM - 1:30 PMObjectives Candida parapsilosis species complex is among the leading agents of invasive candidiasis, notably in neonates and transplant recipients. It exhibits intrinsically reduced susceptibility to echinocandins with increasing reports of acquired resistance to fluconazole from many centers. We evaluated antifungal susceptibility and molecular mechanisms of azole resistance in C. parapsilosis species complex, isolated in the last 5 years.MethodsThe isolates of C. parapsilosis species complex causing infections over a 5-year period (2017-2021) were included in the present study. Species identification of the isolates was performed using MALDI-TOF MS and sequencing of Internal Transcribed Spacer, ITS1. Antifungal susceptibility testing was performed by CLSI broth microdilution in accordance with standard operating procedure described in M27-A3 document. For amphotericin B, itraconazole, and posaconazole, the interpretation of the susceptibility data was done using epidemiological cut-off values provided in CLSI M59 document. The entire coding sequence of ERG11 gene in fluconazole-resistant isolates was PCR-amplified in four overlapping fragments. The sequencing of each fragment was performed by Sanger's bidirectional sequencing method using BigDye termination ready-reaction kit, 3.1. The sequences were assembled and proofread using Seqman software (Laser DNA, Applied Biosystems). The nucleotide sequences were translated into ERG11 protein using nucleotide translation tool, https://web.expasy.org/translate. Multiple sequence alignment with C. parapsilosis reference sequence was performed using BioEdit Sequence Alignment editor.ResultsA total of 580 C. parapsilosis complex clinical isolates were evaluated for antifungal susceptibility. C. parapsilosis sensu stricto, C. orthopsilosis, and C. metapsilosis accounted for 457 (78.8%), 86 (14.8%), and 37 (6.3%), respectively. The isolation distribution revealed an increasing temporal trend over the years. A total of 40 (6.9%) isolates of the species complex exhibited reduced susceptibility to fluconazole, of which 23 were resistant (MIC ≥8 μg/ml) while 17 isolates exhibited susceptible dose-dependent phenotype (MIC, 4 μg/ml). Only two of the fluconazole-resistant isolates were cross-resistant to voriconazole. The resistant isolates were predominantly from adult patients [Median age, IQR; 47 (16-70) years.] The crude mortality rate in resistant cases was 56.5% (13/23). Interestingly, all the fluconazole-resistant isolates were C. parapsilosis sensu stricto, while C. orthopsilosis and C. metapsilosis isolates were susceptible. The fluconazole-resistance rate in the species complex and within the C. parapsilosis sensu stricto was 3.9% (23/599), 4.9% (23/466), respectively. For amphotericin B, the proportion of non-wildtype isolates was 17% (70/411), 25% (9/36), and 0% in C. parapsilosis sensu stricto, C. metapsilosis, and C. orthopsilosis, respectively. For itraconazole, the non-wildtype percentage was 1.7% (7/407), 1.35% (1/74), and 0% in C. parapsilosis sensu stricto, C. orthopsilosis, and C. metapsilosis, respectively. For posaconazole, the non-wildtype percentage was 3.8% (16/413), 2.7% (2/74), and 0% in parapsilosis sensu stricto, C. orthopsilosis and C. metapsilosis, respectively. Sequencing analysis of ERG11 gene revealed two homozygous mutations, Y132F mutation, and R398I in fluconazole-resistant isolates.Conclusions C. parapsilosis species complex infections are on the rise. The increasing azole resistance in C. parapsilosis with higher mortality is a great concern in clinical settings.

P079 Virulence factors and azole-resistant mechanism of Candida tropicalis isolated from candidemia

Poster session 1, September 21, 2022, 12:30 PM - 1:30 PM BackgroundLimited knowledge exists on the virulence factors of Candida tropicalis and the mechanisms of azole resistance that lead to an intensified pathogenicity and treatment failure. We aimed to evaluate the virulence factors and molecular mechanisms of azole resistance among C. tropicalis isolated from patients with candidemia.Materials and MethodsSeveral virulence factors, including extracellular enzymatic activities, cell surface hydrophobicity (CSH), and biofilm formation were evaluated. Antifungal susceptibility pattern and expression level of ERG11, UPC2, MDR1, and CDR1 genes of 8 (4 fluconazole resistance and 4 fluconazole susceptible) clinical C. tropicalis isolates were assessed. The correlation between the virulence factors and antifungal susceptibility patterns was analyzed.ResultsDuring a 4-year study, 45 C. tropicalis isolates were recovered from candidemia patients. The isolates expressed different frequencies of virulence determinants as follows: coagulase 4 (8.9%), phospholipase 5 (11.1%), proteinase 31 (68.9%), esterase 43 (95.6%), hemolysin 44 (97.8%), biofilm formation 45 (100%), and CSH 45(100%). All the isolates were susceptible to amphotericin B and showed the highest resistance to voriconazole. There was a significant positive correlation between micafungin minimum inhibitory concentrations (MICs) and hemolysin production (rs = 0.316). However, we found a negative correlation between fluconazole MICs and esterase production (rs = −0.383). We observed the high expression of ERG11 and UPC2 genes in fluconazole-resistant C. tropicalis isolates.Conclusion Candida tropicalis isolated from candidemia patients extensively displayed capacities for biofilm formation, hemolysis, esterase activity, and hydrophobicity. In addition, the overexpression of ERG11 and UPC2 genes was considered one of the possible mechanisms of azole resistance.

First detection of mutated ERG11 gene in vulvovaginal Candida albicans isolates at Ouagadougou/Burkina Faso

BackgroundVulvovaginal candidiasis is an important cause of morbidity among women due to Candida species. In the last decades, resistance to azoles, first-line antifungals has increased. One molecular mechanism of azole resistance by Candida involves mutations in the ERG11 gene encoding lanosterol 14-α-demethylase, the target enzyme. This study was conducted to identify the clinical Candida species associated in vulvovaginal candidiasis; to determine the rate of antifungal resistance among Candida albicans isolates and to determine mutated ERG11 gene at Saint Camille Hospital in Ouagadougou, Burkina Faso.MethodsAntifungals susceptibility were performed using Kirby–Bauer disk diffusion method. ERG11 gene was detected using conventional PCR in C. albicans isolates resistant to at least one azole.ResultsOut of 262 clinical strains isolated, C. albicans accounted for 59.90%, followed by Candida glabrata 27.86%, Candida famata 7.25%, Candida tropicalis 3.05% and Saccharomyces cerevisiae 1.91%. Resistance rate of fluconazole to C. albicans was 59.54%. ERG11 gene was found in 9.79% of 92 C. albicans strains resistant to azoles.ConclusionsThis detection of mutated ERG11 gene in C. albicans is the first in Burkina Faso and may be a cause of azole resistance in recurrent Candida vulvovaginitis.

Mechanisms of azole antifungal resistance in clinical isolates of Candida tropicalis.

This study was designed to understand the molecular mechanisms of azole resistance in Candida tropicalis using genetic and bioinformatics approaches. Thirty-two azole-resistant and 10 azole-susceptible (S) clinical isolates of C. tropicalis were subjected to mutation analysis of the azole target genes including ERG11. Inducible expression analysis of 17 other genes potentially associated with azole resistance was also evaluated. Homology modeling and molecular docking analysis were performed to study the effect of amino acid alterations in mediating azole resistance. Of the 32 resistant isolates, 12 (37.5%) showed A395T and C461T mutations in the ERG11 gene. The mean overexpression of CDR1, CDR3, TAC1, ERG1, ERG2, ERG3, ERG11, UPC2, and MKC1 in resistant isolates without mutation (R-WTM) was significantly higher (p<0.05) than those with mutation (R-WM) and the sensitive isolates (3.2-11 vs. 0.2-2.5 and 0.3-2.2 folds, respectively). Although the R-WTM and R-WM had higher (p<0.05) CDR2 and MRR1 expression compared to S isolates, noticeable variation was not seen among the other genes. Protein homology modelling and molecular docking revealed that the mutations in the ERG11 gene were responsible for structural alteration and low binding efficiency between ERG11p and ligands. Isolates with ERG11 mutations also presented A220C in ERG1 and together T503C, G751A mutations in UPC2. Nonsynonymous mutations in the ERG11 gene and coordinated overexpression of various genes including different transporters, ergosterol biosynthesis pathway, transcription factors, and stress-responsive genes are associated with azole resistance in clinical isolates of C. tropicalis.

Virulence Factors and Azole-Resistant Mechanism of Candida Tropicalis Isolated from Candidemia.

Limited knowledge exists on the virulence factors of Candida tropicalis and the mechanisms of azole resistance that lead to an intensified pathogenicity and treatment failure. We aimed to evaluate the virulence factors and molecular mechanisms of azole resistance among C. tropicalis isolated from patients with candidemia. Several virulence factors, including extracellular enzymatic activities, cell surface hydrophobicity (CSH), and biofilm formation, were evaluated. Antifungal susceptibility pattern and expression level of ERG11, UPC2, MDR1, and CDR1 genes of eight (4 fluconazole resistance and 4 fluconazole susceptible) clinical C. tropicalis isolates were assessed. The correlation between the virulence factors and antifungal susceptibility patterns was analyzed. During a 4year study, forty-five C. tropicalis isolates were recovered from candidemia patients. The isolates expressed different frequencies of virulence determinants as follows: coagulase 4 (8.9%), phospholipase 5 (11.1%), proteinase 31 (68.9%), esterase 43 (95.6%), hemolysin 44 (97.8%), biofilm formation 45 (100%) and CSH 45(100%). All the isolates were susceptible to amphotericin B and showed the highest resistance to voriconazole. There was a significant positive correlation between micafungin minimum inhibitory concentrations (MICs) and hemolysin production (rs = 0.316). However, we found a negative correlation between fluconazole MICs and esterase production (rs = -0.383). We observed the high expression of ERG11 and UPC2 genes in fluconazole-resistant C. tropicalis isolates. C. tropicalis isolated from candidemia patients extensively displayed capacities for biofilm formation, hemolysis, esterase activity, and hydrophobicity. In addition, the overexpression of ERG11 and UPC2 genes was considered one of the possible mechanisms of azole resistance.

Emergence of Triazole Resistance in Aspergillus spp. in Latin America.

Purpose of ReviewAzole resistance in Aspergillus spp. is becoming a public health problem worldwide. However, data about this subject is lacking in Latin American countries. This review focuses in the epidemiology and molecular mechanisms of azole resistance in Aspergillus spp. emphasizing in Latin America. Data on Aspergillus fumigatus stands out because it is the most prevalent Aspergillus spp. pathogen.Recent FindingsAzole resistance in Aspergillus spp. emergence was linked with intensive use of these antifungals both in the clinical setting and in the environment (as pesticides). Reports on azole-resistant A. fumigatus strains are being constantly published in different countries. Molecular mechanisms of resistance mainly involve substitution in the azole target (CYP51A) and/or overexpression of this gene. However, several other non-CYP51A-related mechanisms were described. Moreover, intrinsically resistant cryptic Aspergillus species are starting to be reported as human pathogens.SummaryAfter a comprehensive literature review, it is clear that azole resistance in Aspergillus spp. is emerging in Latin America and perhaps it is underestimated. All the main molecular mechanisms of azole resistance were described in patients and/or environmental samples. Moreover, one of the molecular mechanisms was described only in South America. Cryptic intrinsic azole-resistant species are also described.

Species distribution, azole resistance and related molecular mechanisms in invasive Candida parapsilosis complex isolates: Increase in fluconazole resistance in 21 years.

Candida parapsilosis complex consists of three species, the prevalence and geographical distribution of which might vary. Increasing rates of fluconazole resistance among C.parapsilosis complex were reported from various centres. Aim of this study was to identify invasive C.parapsilosis complex strains up to species level, explore rates and molecular mechanisms of azole resistance and analyse temporal changes at a single centre. Isolates from blood cultures from 1997 to 2017 were included. Species were identified using RFLP of the SADH gene and confirmed with ITS sequencing when needed. In vitro susceptibility to fluconazole, voriconazole and posaconazole was tested and evaluated using EUCAST guidelines. Sequences of ERG11 and MRR1 genes were analysed for fluconazole non-susceptible isolates. A total of 283 isolates from 181 patients were tested for azole susceptibility. All were C.parapsilosis sensu stricto, except one C.orthopsilosis. All three azoles were effective against 213 of the isolates from 135 patients, including one C.orthopsilosis. Fluconazole resistance was 13.3% (24/181 patients). While the first fluconazole-resistant isolates were detected in 2004, increase was evident after 2011. In ERG11, Y132F mutation was the most common among fluconazole non-susceptible isolates (71.7%), followed by G458S (10.9%) and D421N (4.3%). In MRR1, R405K (56.5%) and G927C (8.7%) were detected. However, association of these mutations to azole resistance is yet to be investigated. Rising azole resistance rates in C.parapsilosis sensu stricto isolates particularly after 2011 were of concern. The well-known Y132F mutation was the predominant mechanism of azole resistance while accompanied with other genetic mutations.

Implication of efflux pumps and ERG11 genes in resistance of clinical Trichosporon asahii isolates to fluconazole.

Introduction. Trichosporon asahii has been recognized as an opportunistic agent having a limited sensitivity to antifungal treatment.Hypothesis/Gap Statement. Molecular mechanisms of azole resistance have been rarely reported for Trichosproron asahii. Similar to other fungi, we hypothesized that both ERG11 gene mutation and efflux pumps genes hyper-expression were implicated.Aim. The current work aimed to study the sensitivity of clinical T. asahii isolates to different antifungal agents and to explore their resistance mechanisms by molecular methods including real-time PCR and gene sequencing.Methods. The sensitivity of T. asahii isolates to fluconazole, amphotericin B and voriconazole was estimated by the Etest method. Real-time PCR was used to measure the relative expression of Pdr11, Mdr and ERG11 genes via the ACT1 housekeeping gene. Three pairs of primers were also chosen to sequence the ERG11 gene. This exploration was followed by statistical study including the receiver operating characteristic (ROC) curve analysis to identify a relationship between gene mean expression and the sensitivity of isolates.Results. In 31 clinical isolates, the resistance frequencies were 87, 16.1 and 3.2 %, respectively, for amphotericin B, fluconazole and voriconazole. Quantitative real-time PCR demonstrated that only Mdr over-expression was significantly associated with FCZ resistance confirmed by univariate statistical study and the ROC curve analysis (P <0.05). The ERG11 sequencing revealed two mutations H380G and S381A in TN325U11 (MIC FCZ=8 µg ml-1) and H437R in TN114U09 (MIC FCZ=256 µg ml-1) in highly conserved regions (close to the haem-binding domain) but their involvement in the resistance mechanism has not yet been assigned.Conclusion. T. asahii FCZ resistance mechanisms are proven to be much more complex and gene alteration sequence and/or expression can be involved. Only Mdr gene over-expression was significantly associated with FCZ resistance and no good correlation was observed between FCZ and VCZ MIC values and relative gene expression. ERG11 sequence alteration seems to play a major role in T. asahii FCZ resistance mechanism but their involvement needs further confirmation.

The C2H2 Transcription Factor SltA Contributes to Azole Resistance by Coregulating the Expression of the Drug Target Erg11A and the Drug Efflux Pump Mdr1 in Aspergillus fumigatus.

The emergence of azole-resistant fungal pathogens has posed a great threat to public health worldwide. Although the molecular mechanism of azole resistance has been extensively investigated, the potential regulators of azole resistance remain largely unexplored. In this study, we identified a new function of the fungal specific C2H2 zinc finger transcription factor SltA (involved in the salt tolerance pathway) in the regulation of azole resistance of the human fungal pathogen Aspergillus fumigatus A lack of SltA results in an itraconazole hypersusceptibility phenotype. Transcriptional profiling combined with LacZ reporter analysis and electrophoretic mobility shift assays (EMSA) demonstrated that SltA is involved in its own transcriptional regulation and also regulates the expression of genes related to ergosterol biosynthesis (erg11A, erg13A, and erg24A) and drug efflux pumps (mdr1, mfsC, and abcE) by directly binding to the conserved 5'-AGGCA-3' motif in their promoter regions, and this binding is dependent on the conserved cysteine and histidine within the C2H2 DNA binding domain of SltA. Moreover, overexpression of erg11A or mdr1 rescues sltA deletion defects under itraconazole conditions, suggesting that erg11A and mdr1 are related to sltA-mediated itraconazole resistance. Most importantly, deletion of SltA in laboratory-derived and clinical azole-resistant isolates significantly attenuates drug resistance. Collectively, we have identified a new function of the transcription factor SltA in regulating azole resistance by coordinately mediating the key azole target Erg11A and the drug efflux pump Mdr1, and targeting SltA may provide a potential strategy for intervention of clinical azole-resistant isolates to improve the efficiency of currently approved antifungal drugs.

Detection of ERG11 Overexpression in Candida albicans isolates from environmental sources and clinical isolates treated with inhibitory and subinhibitory concentrations of fluconazole.

Candida species can cause serious infection in patients with changes in defence mechanisms and/or when anatomical barriers are compromised. Mutations and overexpression in the ERG11 gene are described as molecular mechanisms of azole resistance. Information is limited on these mechanisms in the presence of subinhibitory concentrations of fluconazole. This study aimed to evaluate the expression of ERG11 gene from Candida albicans isolates, from clinical and hospital environments, in the absence and presence of inhibitory and subinhibitory concentrations of fluconazole. The American Type Culture Collection 10231 strain, five clinical isolates and three isolates from hospital environment colonisation were exposed to inhibitory and subinhibitory concentrations of fluconazole. Susceptibility tests were performed according to EUCAST 7.1 guidelines, and the relative expression analysis of ERG11 was performed by qPCR. Differences in response to fluconazole concentrations were observed, with the exception only one clinical isolate when treated with 1/4 of the FLU-minimum inhibitory concentration (MIC). All the other isolates, regardless of the isolation source, had an increase in expression. The overexpression occurred in a very broad range, from 1.086 to 126.105 times. In general, treatment with the highest dose of fluconazole (MIC) was the one that most influenced the ERG11 expression, followed by treatments with 1/2 and 1/4 MIC. The increased expression of ERG11 by Calbicans in the presence of different concentrations of fluconazole is relevant, raising concerns in the care and cleaning of the hospital environment and the prophylactic use of fluconazole that could lead to the selection of potential azole-resistant isolates.

Antifungal susceptibility profile and molecular identification of Cyp51C mutations in clinical and environmental isolates of Aspergillus flavus from Argentina.

The emergence of azole resistance in non-fumigatus Aspergillus strains is on the raise. To study the susceptibility profiles and the molecular mechanisms of azole resistance of environmental and clinical strains of Aspergillus flavus from Argentina. Thirty-five Aflavus isolates (18 from soybean seeds and chickpea seeds and 17 from the clinic) were analysed for amphotericin B and azole resistance using the standard microbroth dilution method according to CLSI M38-A2 guidelines. Sequencing analysis of the cyp51 genes was conducted in those isolates displaying high MICs values to itraconazole, voriconazole and/or posaconazole. Among the environmental isolates, 33.3% of them showed high MIC values for at least one triazole whereas 23.5% of the clinical isolates displayed high MIC values for amphotericin B. Point mutations in the Cyp51C gene were recorded in most environmental isolates with non-wild-type MIC values. Susceptibility differences among environmental Aflavus isolates might suggest the possibility of native resistance to certain triazole antifungals used in the clinic. To the best of our knowledge, this is the first report of antifungal screening of environmental strains of Aflavus in soybean seeds and chickpea seeds from Argentina that showed increased resistance to voriconazole and itraconazole in comparison to clinical strains.

High prevalence of triazole-resistant Aspergillus fumigatus sensu stricto in an Argentinean cohort of patients with cystic fibrosis.

Triazole resistance in Aspergillus fumigatus sensu stricto due to mutations in the cyp51A gene has been widely reported. Data from Argentina, and particularly from cystic fibrosis (CF) patients, are limited. To investigate the prevalence and molecular mechanisms of azole resistance in A. fumigatus sensu stricto recovered from this population. Ninety-three A. fumigatus isolates from 50 CF patients were retrospectively analysed for azole resistance using the standard microbroth dilution method according to CLSI M38-A2 guidelines. Sequencing analysis of the cyp51A gene and its promoter region was conducted in those isolates displaying high MIC values to itraconazole, voriconazole and/or posaconazole. Overall, 14% of isolates displayed high MIC values to at least one azole. Of them, 30.7% had the mutation TR34-L98H. No mutations in the cyp51A gene or its promoter were found in the remaining non-wild-type strains. Therefore, other mechanisms associated with azole resistance can be highly prevalent in these isolates. To the best of our knowledge, this is the first study in Latin America reporting azole-resistant A. fumigatus strains recovered from respiratory secretions of CF patients. Noteworthy, the prevalence of azole resistance in A. fumigatus sensu stricto in the studied Argentinean CF population is alarmingly high.

Dynamics of in vitro development of azole resistance in Candida tropicalis

ObjectivesIncreasing incidence of azole resistance in Candida tropicalis, especially to fluconazole, has been seen in Asian countries including India. Limited knowledge is available on the molecular mechanisms associated with the development of azole resistance in C. tropicalis. The present study examined the dynamics of in vitro azole resistance in C. tropicalis after prolonged treatment with fluconazole. MethodsNine fluconazole-susceptible isolates of C. tropicalis were used in this study. Fluconazole resistance was induced experimentally in C. tropicalis isolates. The stability of induced resistance and cross-resistance to other azoles was examined. The molecular mechanisms of azole resistance were assessed by measuring the expression and mutation analysis of different genes. ResultsVarying degrees of resistance [five with minimum inhibitory concentrations (MICs) ≤32 mg/L and four with MICs ≥128 mg/L] were noticed, and the resistance was developed in 3 months. Of the nine resistant isolates, four induced resistant isolates with MICs ≥128 mg/L presented temporal resistance stability up to 10 subcultures. These four isolates presented cross-resistance to other azoles and also an inducible overexpression of transporters (CDR1, CDR2, CDR3 and MDR1), ergosterol biosynthesis pathway genes (ERG1, ERG2, ERG3 and ERG11), transcription factors (TAC1 and UPC2) and stress-responsive genes (HSP90 and MKC1) was noticed. No mutations were seen in any of the four genes (ERG1, ERG3, ERG11 and UPC2) tested. ConclusionsCandida tropicalis isolates adapt themselves in the presence of continuous drug exposure and switch back to being susceptible in the absence of the drug. The acquisition of resistance in C. tropicalis is mediated by the overexpression of different resistance-related genes without any molecular alterations.

Antifungal susceptibility, genotyping, resistance mechanism, and clinical profile of Candida tropicalis blood isolates.

Candida tropicalis is one of the major candidaemia agents, associated with the highest mortality rates among Candida species, and developing resistance to azoles. Little is known about the molecular mechanisms of azole resistance, genotypic diversity, and the clinical background of C. tropicalis infections. Consequently, this study was designed to address those questions. Sixty-four C. tropicalis bloodstream isolates from 62 patients from three cities in Iran (2014–2019) were analyzed. Strain identification, antifungal susceptibility testing, and genotypic diversity analysis were performed by MALDI-TOF MS, CLSI-M27 A3/S4 protocol, and amplified fragment length polymorphism (AFLP) fingerprinting, respectively. Genes related to drug resistance (ERG11, MRR1, TAC1, UPC2, and FKS1 hotspot9s) were sequenced. The overall mortality rate was 59.6% (37/62). Strains were resistant to micafungin [minimum inhibitory concentration (MIC) ≥1 μg/ml, 2/64], itraconazole (MIC > 0.5 μg/ml, 2/64), fluconazole (FLZ; MIC ≥ 8 μg/ml, 4/64), and voriconazole (MIC ≥ 1 μg/ml, 7/64). Pan-azole and FLZ + VRZ resistance were observed in one and two isolates, respectively, while none of the patients were exposed to azoles. MRR1 (T255P, 647S), TAC1 (N164I, R47Q), and UPC2 (T241A, Q340H, T381S) mutations were exclusively identified in FLZ-resistant isolates. AFLP fingerprinting revealed five major and seven minor genotypes; genotype G4 was predominant in all centers. The increasing number of FLZ-R C. tropicalis blood isolates and acquiring FLZ-R in FLZ-naive patients limit the efficiency of FLZ, especially in developing countries. The high mortality rate warrants reaching a consensus regarding the nosocomial mode of C. tropicalis transmission.

Molecular mechanisms of azole resistance in Candida tropicalis isolates causing invasive candidiasis in China

ObjectiveWe investigated molecular mechanisms responsible for azole resistance in Candida tropicalis isolates. MethodsWe studied 507 C. tropicalis isolates causing invasive candidiasis from ten hospitals over 5 years. Antifungal susceptibility was determined by broth microdilution methods. Point mutations in the C. tropicalis ERG11 gene that may confer azole resistance were explored and verified. The expression levels of ERG11, CYTb, MDR1 and CDR1 genes were compared in 20 fluconazole-susceptible and 20 fluconazole-resistant isolates. ResultsFluconazole-susceptible, -susceptible dose-dependent and -resistant strains accounted for 76.7% (389/507), 10.5% (53/507) and 12.8% (65/507) of C. tropicalis isolates, respectively. The ERG11 mutation A395T/W occurred in 10.7% (54/507) of isolates, all of which were resistant to fluconazole. The nucleotide mutation C461T/Y was the second most common (50/507 isolates, 9.9%), and all isolates carrying C461T/Y also had the mutation A395T/W. However, the presence of C461T did not contribute to the azole-resistant phenotype. Substitutions V125A, Y257H and G464S (<2% of isolates), which were reported for the first time in C. tropicalis, also conferred fluconazole non-susceptible phenotypes. Compared with fluconazole susceptible isolates, fluconazole-resistant isolates had higher ERG11 (fold expression level 1.42 versus 0.79, p < 0.01) but lower CYTb (fold expression level 1.26 versus 2.67, p < 0.01) gene expression levels. Three azole-resistant isolates carrying the wild-type ERG11 gene had higher levels of CDR1 and MDR1 expression. ConclusionsERG11 missense mutations were the major mechanism responsible for azole resistance in C. tropicalis isolates, but overexpression of ERG11, CDR1 and MDR1, as well as reduced expression of CYTb, also contributed to resistance.