Fluconazole Minimal Inhibitory Concentrations Research Articles

Antifungal Resistance in Cryptococcal Infections.

Antifungal therapy, especially with the azoles, could promote the incidence of less susceptible isolates of Cryptococcus neoformans and C. gattii species complexes (SC), mostly in developing countries. Given that these species affect mostly the immunocompromised host, the infections are severe and difficult to treat. This review encompasses the following topics: 1. infecting species and their virulence, 2. treatment, 3. antifungal susceptibility methods and available categorical endpoints, 4. genetic mechanisms of resistance, 5. clinical resistance, 6. fluconazole minimal inhibitory concentrations (MICs), clinical outcome, 7. environmental influences, and 8. the relevance of host factors, including pharmacokinetic/pharmacodynamic (PK/PD) parameters, in predicting the clinical outcome to therapy. As of now, epidemiologic cutoff endpoints (ECVs/ECOFFs) are the most reliable antifungal resistance detectors for these species, as only one clinical breakpoint (amphotericin B and C. neoformans VNI) is available.

Therapeutic Switching of Rafoxanide: a New Approach To Fighting Drug-Resistant Bacteria and Fungi.

Control and management of life-threatening bacterial and fungal infections are a global health challenge. Despite advances in antimicrobial therapies, treatment failures for resistant bacterial and fungal infections continue to increase. We aimed to repurpose the anthelmintic drug rafoxanide for use with existing therapeutic drugs to increase the possibility of better managing infection and decrease treatment failures. For this purpose, we evaluated the antibacterial and antifungal potential of rafoxanide. Notably, 70% (70/100) of bacterial isolates showed multidrug resistance (MDR) patterns, with higher prevalence among human isolates (73.5% [50/68]) than animal ones (62.5% [20/32]). Moreover, 22 fungal isolates (88%) were MDR and were more prevalent among animal (88.9%) than human (87.5%) sources. We observed alarming MDR patterns among bacterial isolates, i.e., Klebsiella pneumoniae (75% [30/40; 8 animal and 22 human]) and Escherichia coli (66% [40/60; 12 animal and 28 human]), and fungal isolates, i.e., Candida albicans (86.7% [13/15; 4 animal and 9 human]) and Aspergillus fumigatus (90% [9/10; 4 animal and 5 human]), that were resistant to at least one agent in three or more different antimicrobial classes. Rafoxanide had antibacterial and antifungal activities, with minimal inhibitory concentration (MICs) ranging from 2 to 128 μg/mL. Rafoxanide at sub-MICs downregulated the mRNA expression of resistance genes, including E. coli and K. pneumoniae blaCTX-M-1, blaTEM-1, blaSHV, MOX, and DHA, C. albicans ERG11, and A. fumigatus cyp51A. We noted the improvement in the activity of β-lactam and antifungal drugs upon combination with rafoxanide. This was apparent in the reduction in the MICs of cefotaxime and fluconazole when these drugs were combined with sub-MIC levels of rafoxanide. There was obvious synergism between rafoxanide and cefotaxime against all E. coli and K. pneumoniae isolates (fractional inhibitory concentration index [FICI] values ≤ 0.5). Accordingly, there was a shift in the patterns of resistance of 16.7% of E. coli and 22.5% of K. pneumoniae isolates to cefotaxime and those of 63.2% of C. albicans and A. fumigatus isolates to fluconazole when the isolates were treated with sub-MICs of rafoxanide. These results were confirmed by in silico and mouse protection assays. Based on the in silico study, one possible explanation for how rafoxanide reduced bacterial resistance is through its inhibitory effects on bacterial and fungal histidine kinase enzymes. In short, rafoxanide exhibited promising results in overcoming bacterial and fungal drug resistance. IMPORTANCE The drug repurposing strategy is an alternative approach to reducing drug development timelines with low cost, especially during outbreaks of disease caused by drug-resistant pathogens. Rafoxanide can disrupt the abilities of bacterial and fungal cells to adapt to stress conditions. The coadministration of antibiotics with rafoxanide can prevent the failure of treatment of both resistant bacteria and fungi, as the resistant pathogens could be made sensitive upon treatment with rafoxanide. From our findings, we anticipate that pharmaceutical companies will be able to utilize new combinations against resistant pathogens.

Exposure of Cryptococcus neoformans to Seven Commonly Used Agricultural Azole Fungicides Induces Resistance to Fluconazole as Well as Cross-Resistance to Voriconazole, Posaconazole, Itraconazole and Isavuconazole.

Cross-resistance to medical azoles by exposure to azole pesticides is well documented for Aspergillus family fungi but is poorly evaluated for other environmental pathogen fungi, particularly for yeasts belonging to the Cryptococcus neoformans/Cryptococcus gattii species complexes. One thousand C. neoformans yeast were exposed to various concentrations of seven different commonly used azole pesticides. Clones surviving exposure were picked randomly, and their minimal inhibitory concentrations (MICs) of fluconazole, voriconazole, posaconazole, itraconazole and isavuconazole were assessed. Depending on the pesticide used for exposure, up to 13.3% of selected Cryptococcus colonies showed a phenotype of resistance to fluconazole, and among them, several showed cross-resistance to another or several other medical azoles. Molecular mechanisms involved in the resistance setups seem to be dependent on ERG11 and AFR1 gene overexpression. Exposure to any of the seven azole pesticides tested is capable of increasing the MIC of fluconazole in C. neoformans, including up to the level of the fluconazole-resistant phenotype, as well as generating cross-resistance to other medical azoles in some cases.

Acquired fluconazole resistance and genetic clustering in Diutina (Candida) catenulata from clinical samples

ObjectivesDiutina (Candida) catenulata is an ascomycetous yeast isolated from environmental sources and animals, occasionally infecting humans. The aim of this study is to shed light on the in vitro antifungal susceptibility and genetic diversity of this opportunistic yeast. MethodsForty-five D. catenulata strains isolated from various sources (including human and environmental sources) and originating from nine countries were included. Species identification was performed using matrix-assisted laser desorption/ionization time-of-flight mass spectrometry and confirmed via internal transcribed spacer ribosomal DNA barcoding. In vitro antifungal susceptibility was determined for seven systemic antifungals via the gradient strip method after 48 hours of incubation at 35°C using Etest® (Biomérieux) or Liofilchem® strips. Isolates exhibiting fluconazole minimal inhibitory concentrations (MICs) of ≥8 μg/mL were investigated for mutations in the ERG11 gene. A novel microsatellite genotyping scheme consisting of four markers was developed to assess genetic diversity. ResultsMIC ranges for amphotericin B, caspofungin, micafungin, isavuconazole, and posaconazole were 0.19–1 μg/mL, 0.094–0.5 μg/mL, 0.012–0.064 μg/mL, 0.003–0.047 μg/mL, and 0.006–0.032 μg/mL, respectively. By comparison, a broad range of MICs was noted for fluconazole (0.75 to >256 μg/mL) and voriconazole (0.012–0.38 mg/L), the higher values being observed among clinical strains. The Y132F amino acid substitution, associated with azole resistance in various Candida species (C. albicans, C. tropicalis, C. parapsilosis, and C. orthopsilosis), was the main substitution identified. Although microsatellite typing showed extensive genetic diversity, most strains with high fluconazole MICs clustered together, suggesting human-to-human transmission or a common source of contamination. DiscussionThe high rate of acquired fluconazole resistance among clinical isolates of D. catenulata is of concern. In this study, we highlight a link between the genetic diversity of D. catenulata and its antifungal resistance patterns, suggesting possible clonal transmission of resistant isolates.

Distribution and Fluconazole Susceptibility Pattern of Fungi Isolated from Saloon Equipment in Rivers State, Nigeria

The distribution and susceptibility pattern of fungal isolates from barbing equipment to Fluconazlole in barber shops distributed in three major cities; Bori, Omoku, and Port Harcourt in Rivers State, Nigeria were investigated. The fungal load including dermatophytes on the equipment (brush, clipper and comb) were determined using swab plate technique in which Sabouraud dextrose agar and dermatophyte test medium were used as the culture medium. Inoculated plates were incubated at 25°C. Antifungal Susceptibility testing was carried in which fluconazole was used as the antifungal agent at concentrations of 100mg/ml, 50mg/ml, 25mg/ml, and 12.5mg/ml concentration using two-fold dilution. The mean range of the fungal counts for clipper, brush and comb were: 34.34x102 to 49.0x102 CFU/cm2, 66.95 to 93.26 CFU/cm2 and 40.09 to 74.61 x102 CFU/cm2, respectively. Brush had the highest fungal counts followed by the comb while the clipper had the least fungal counts. The fungal counts recorded in brushes were significantly higher (p≥0.05) than those recorded for the clippers. Total of forty-four fungal isolates belonging to six genera and their percentage occurrence include; Aspergillus flavus (11.36%) Aspergillus terrus (11.36%), Fusarium solani (22.72%), Mucor indicus (15.91%), Rhizopus nigricans (15.91%), Trichophyton rubrum (4.54%) and Penicillium italicum (18.2%). The susceptibility pattern showed that except for Trichophyton rubrum, all fungal isolates were completely inhibited at 100mg/ml concentration of fluconazole. Also, except for Mucor indicus, the Minimal inhibitory Concentration of fluconazole was recorded at 12.5mg/ml. The occurrence of these organisms in barbing equipment calls for concern and the need for regulation of the barbing industry to prevent disease outbreaks is recommended.

Does DHN-Melanin Always Protect Fungi against Antifungal Drugs? The Fonsecaea/Micafungin Paradigm

Several human pathogenic fungi produce melanin. One of its properties during parasitism is the protection against antifungal drugs. This occurs with the agents of chromoblastomycosis, in which DHN-melanin reduces antifungal susceptibility to terbinafine and itraconazole. Since these agents are resistant to some antifungal drugs, we investigated the role of DHN-melanin on the Fonsecaea susceptibility to amphotericin B, micafungin, fluconazole, and flucytosine, drugs that usually present high minimal inhibitory concentrations (MIC) to this genus. Seven strains from three Fonsecaea human pathogenic species were treated with tricyclazole, a DHN-melanin inhibitor, and the MIC of the treated and untreated cells were compared. A survival assay was performed to confirm the alterations in the susceptibility of strains with reduced melanization, and the chitin levels of the strains were estimated by fluorescence. Tricyclazole did not affect fluconazole and flucytosine MIC, while melanin inhibition increased susceptibility to amphotericin B. Surprisingly, DHN-melanin inhibition decreased the susceptibility to micafungin. Survival assays confirmed this result on five strains. Cell wall chitin levels of the strains were not associated with the decrease in micafungin susceptibility. The results show that DHN-melanin does not have a role in the intrinsic resistance of Fonseacaea spp. to amphotericin B, fluconazole, and flucytosine, and its inhibition may promote micafungin resistance.

Investigation of fluconazole heteroresistance in clinical and environmental isolates of Cryptococcus neoformans complex and Cryptococcus gattii complex in the state of Amazonas, Brazil

Cryptococcosis affects many people and is caused by fungi of the Cryptococcus neoformans/Cryptococcus gattii complexes. These agents appear to become more resistant to antifungals when exposed to increasing concentrations of antifungals due to a phenomenon called heteroresistance.

Candida albicans blastospores and hyphae respond differentially to fluconazole: additional virulence factor of germination process

Background: The morphologic transition from yeasts (blastospores) to hyphae, through the germination process, is a crucial virulence factor of Candida albicans ( C. albicans), as it enhances adherence, tissue invasion and biofilm formation. The study aimed at comparing fluconazole susceptibility patterns of C. albicans yeast and germinated forms. Methods: Six C. albicans strains, including C. albicans ATCC 10231 and 5 clinical isolates were tested in yeast forms and germinated forms for fluconazole susceptibility using CLSI M27-A3 broth microdilution and CLSI M44-A2 disk diffusion reference methods. Results: Fluconazole minimal inhibitory concentrations (MICs) were 0.125-1 µg/ml and 0.25-4 µg/ml for yeasts and germinated forms, respectively. The sensitivities of yeasts were higher than those of their corresponding germinated forms with 1 to 4-fold dilutions differences. The MIC50s of yeasts and germinated forms were 0.125 and 1 µg/ml, respectively, with 3-fold dilution difference, while MIC90s were 1 and 4 µg/ml for yeasts and germinated forms, respectively, with 2-fold dilution difference. Means of inhibition zones were 31-46.7 mm and 29.3-43.7 mm for yeasts and germinated forms, respectively. The germinated forms of all tested strains had inhibition zones smaller than those of their corresponding yeast forms with 0.2-4.8 mm differences. There was significant statistical difference in sizes of inhibition zones between yeasts and germinated forms (p = 0.043). Conclusions: Yeast and hyphae of C. albicans, both in planktonic state, respond differentially to fluconazole, as the hyphae are less sensitive than their yeasts counterparts, which can be considered as a virulence factor for hyphae, which should be considered in treatment plans of candidal infections.

In vitro antifungal activity of pelgipeptins against human pathogenic fungi and Candida albicans biofilms.

Systemic mycoses have become a major cause of morbidity and mortality, particularly among immunocompromised hosts and long-term hospitalized patients. Conventional antifungal agents are limited because of not only their costs and toxicity but also the rise of resistant strains. Lipopeptides from Paenibacillus species exhibit antimicrobial activity against a wide range of human and plant bacterial pathogens. However, the antifungal potential of these compounds against important human pathogens has not yet been fully evaluated, except for Candida albicans. Paenibacillus elgii produces a family of lipopeptides named pelgipeptins, which are synthesized by a non-ribosomal pathway, such as polymyxin. The present study aimed to evaluate the activity of pelgipeptins produced by P. elgii AC13 against Cryptococcus neoformans, Paracoccidioides brasiliensis, and Candida spp. Pelgipeptins were purified from P. elgii AC13 cultures and characterized by high-performance liquid chromatography (HPLC) and mass spectrometry (MALDI-TOF MS). The in vitro antifugal activity of pelgipeptins was evaluated against C. neoformans H99, P. brasiliensis PB18, C. albicans SC 5314, Candida glabrata ATCC 90030, and C. albicans biofilms. Furthermore, the minimal inhibitory concentration (MIC) was determined according to the CLSI microdilution method. Fluconazole and amphotericin B were also used as a positive control. Pelgipeptins A to D inhibited the formation and development of C. albicans biofilms and presented activity against all tested microorganisms. The minimum inhibitory concentration values ranged from 4 to 64 µg/mL, which are in the same range as fluconazole MICs. These results highlight the potential of pelgipeptins not only as antimicrobials against pathogenic fungi that cause systemic mycoses but also as coating agents to prevent biofilm formation on medical devices.

The epidemiology, genotypes, antifungal susceptibility of Trichosporon species, and the impact of voriconazole on Trichosporon fungemia patients

Invasive Trichosporon infections are emerging, but association of different therapeutic management of Trichosporon fungemia and clinical outcomes were rarely reported. This study investigates the epidemiology, species distribution and genotypes of trichosporonosis in Taiwan, and identified the predictors of clinical outcomes in patients with Trichosporon fungemia. Strains collected from four medical centers in Taiwan, during 2010-2018. Species identification was confirmed by sequencing of IGS1 region, and antifungal susceptibility was performed using Sensititre YeastOne panel. Among 115 isolates, Trichosporon asahii was the leading species (73.0%), followed by Trichosporon dermatis (11.3%), Trichosporon faecales (6.1%), and Trichosporon montevideense (5.2%). Of the 84 T. asahii isolates, genotype 1 was the predominant (41.7%). High fluconazole minimal inhibitory concentration (MICs,≧8μg/mL) were observed for 70.2% T. asahii isolates and 16.1% non-asahii Trichosporon isolates. Posaconazole and voriconazole possess the most potent antifungal activity against all Trichosporon isolates, with geometric mean values of 0.251μg/mL and 0.111μg/mL, respectively. Fifty-three isolates collected from blood cultures, and 42 patients with fungemia enrolled for the Kaplan-Meier plot which revealed that voriconazole treatment had a significantly better survival rate compared with those without (p=0.042). In multivariate analysis, source control (odds ratio [OR]: 0.13 95%CI [confidence interval]: 0.02-0.83, p=0.031) and voriconazole use (OR: 0.11 95%CI: 0.02-0.74, p=0.023) are independent predictors of 14-day mortality. This is the largest series of Trichosporon fungemia up till the present moment. Voriconazole therapy and source control play important roles in 14-day mortality.

Antifungal Activity and Potential Mechanism of Panobinostat in Combination With Fluconazole Against Candida albicans.

Invasive fungal infections are an emerging problem worldwide, which bring huge health challenges. Candida albicans, the most common opportunistic fungal pathogen, can cause bloodstream infections with high mortality in susceptible hosts. At present, available antifungal agents used in clinical practice are limited, and most of them also have some serious adverse effects. The emergence of drug resistance because of the wide use of antifungal agents is a new limitation to successful patient therapy. Drug combination therapy is increasingly becoming a way to enhance antifungal efficacy, and reduce drug resistance and potential toxicity. Panobinostat, as a pan-histone deacetylase inhibitor, has been approved by the United States Food and Drug Administration as novel antitumor agents. In this study, the antifungal effects and mechanisms of panobinostat combined with fluconazole (FLC) against C. albicans were explored for the first time. The results indicated that panobinostat could work synergistically with FLC against resistant C. albicans, the minimal inhibitory concentration (MIC) of panobinostat could decrease from 128 to 0.5–2 μg/ml and the MIC of FLC could decrease from >512 to 0.25–0.5 μg/ml, and the fractional inhibitory concentration index (FICI) value ranged from 0.0024 to 0.0166. It was not only synergized against planktonic cells but also against C. albicans biofilms performed ≤8 h when panobinostat is combined with fluconazole; the sessile MIC (sMIC) of panobinostat could decrease from >128 to 0.5–8 μg/ml and the sMIC of FLC from >1024 to 0.5–2 μg/ml, and the FICI value was <0.5. The Galleria mellonella infection model was used to evaluate the in vivo effect of the drug combination, and the result showed that the survival rate could be improved obviously. Finally, we explored the synergistic mechanisms of the drug combination. The hyphal growth, which plays roles in drug resistance, was found to be inhibited, and metacaspase which is related to cell apoptosis was activated (p < 0.01), whereas the synergistic effects were proven not to be related to the efflux pumps (p > 0.05). These findings might provide novel insights into the antifungal drug discovery and the treatment of candidiasis caused by C. albicans.

Molecular typing and in vitro resistance of Cryptococcus neoformans clinical isolates obtained in Germany between 2011 and 2017

Cryptococcosis is a fungal infection of the central nervous system predominantly caused by Cryptococcus neoformans in immunocompromised patients. In several countries worldwide, up to 50% of isolates show in vitro resistance to clinically used antifungals including fluconazole. No prospective data on susceptibility to antifungal drugs are available for Germany. In this study, we characterised all C. neoformans isolates collected from individual patients’ samples at the German reference laboratory for cryptococcosis 2011 and 2017 (n = 133) by multi-locus sequence typing and phenotypic drug susceptibility testing. We identified serotype A/genotype VNI isolates belonging to clonal complexes previously described from Europe, Africa, Asia and South America as the most prevalent agents of cryptococcosis in Germany. Overall, we observed minimal inhibitory concentrations (MICs) above the epidemiological cut-offs (ECVs) in 1.6% of isolates regarding fluconazole and 2.3% of isolates regarding 5-flucytosine. Here, two C. neoformans var. grubii isolates displayed decreased drug susceptibility to fluconazole, one of them additionally to 5-flucytosine. We also found 5-flucytosine MICs above the ECV for two C. neoformans var. neoformans isolates. We identified a novel mutation in the ERG11 gene which might be associated with the elevated fluconazole MIC in one of the isolates. The clinical importance of the detected in vitro resistance is documented by patient histories showing relapsed infection or primary fatal disease. Of note, sertraline demonstrated antifungal activity comparable to previous reports. Systematic collection of susceptibility data in combination with molecular typing of C. neoformans is important to comprehensively assess the spread of isolates and to understand their drug resistance patterns.

Species Distribution and Antifungal Susceptibility of Yeasts Isolated from Ear Specimens

Background Candida auris was first isolated from the ears of Japanese and Korean patients. However, the prevalence of yeast isolates from ear cultures and their antifungal susceptibility profiles in these nations remain unclear. Methods We assessed yeast isolates recovered from ear cultures from a university hospital in Korea over a 4-year period from January 2014 to December 2017. Species identification was performed by matrix-assisted laser desorption/ionization time-of-flight mass spectrometry and/or sequence analysis. Antifungal minimal inhibitory concentrations (MICs) were determined using the broth microdilution method of the Clinical and Laboratory Standards Institute. Results Among 81 non-duplicate isolates from ear cultures, Cadida parapsilosis was the most frequently detected yeast species (34.6%), followed by C. auris (28.4%), Candida metapsilosis (9.9%), Candida orthopsilosis (8.6%), Candida albicans (7.4%), and others (11.1%). The MICs of the isolates were 0.125 to > 64 µg/mL, ≤0.03 to 4 µg/mL, 0.25 to 1 µg/mL, 0.125 to 1 µg/mL, and ≤0.03 to 2 µg/mL for fluconazole, voriconazole, amphotericin B, caspofungin, and micafungin, respectively. Of the 81 isolates, 44.4% (36/81) showed decreased susceptibility to fluconazole (MIC ≥4 µg/mL). Of the 23 C. auris isolates, 19 (82.6%) had a fluconazole MIC of ≥32 µg/mL. None of the isolates showed resistance to amphotericin B or echinocandins. Most of these patients suffered from chronic otitis media (84%). Conclusion Candida parapsilosis complex and C. auris were the yeast species identified most frequently from ear cultures and they exhibited a high rate of fluconazole non-susceptibility, particularly C. auris.

Susceptibility testing of Candida glabrata clinical strains to echinocandins using SensititreTM YeastOneTM system

Objective. To determine susceptibility of C. glabrata isolates to anidulafungin, caspofungin and micafungin using the SensititreTM YeastOneTM system. Materials and Methods. C. glabrata isolates were taken prospectively from clinical specimens or from strains collections in the participating sites. Susceptibility determination was performed using SensititreTM YeastOneTM (YO10 panel) according to the manufacturer’s guidance, and results were interpreted with M27-A3 CLSI guidelines. Susceptibility of C. glabrata to fluconazole was also determined in order to assess possible correlations of echinocandins and fluconazole minimal inhibitory concentrations (MICs) in resistant strains. Results. A total of 59 C. glabrata strains were tested. The strains were isolated mostly from peripheral blood (44%). Among clinically significant medical conditions/risk factors and co-morbidities, central venous catheter, solid tumors, and abdominal surgery were identified in 20 (33.9%), 19 (32.2%), and 14 (23.7%) patients, respectively. Most MIC values of echinocandins were 0.015 and 0.03 mg/L. Caspofungin has slightly higher MIC values than those of anidulafungin and micafungin. No isolates were resistant to any of the echinocandins. The only 2 patients were receiving echinocandin therapy at the time of taking biosamples (with no reported information about treatment efficacy); those strains were also susceptible to all echinocandins. All C. glabrata strains were susceptible dose-dependent to fluconazole with MIC values between 2 and 32 mg/L. Conclusions. All of the echinocandins have a high and comparable in vitro activity against C. glabrata, including strains which are susceptible dose-depended to fluconazole. More prospective studies are needed to investigate the long-term trends in susceptibility profiles of pathogens causing candidiasis, especially C. glabrata.

Distribution and antifungal susceptibility of yeasts isolates from intensive care unit patients.

Yeasts frequently colonize non-sterile sites in the body. The aim of the study was to determine distribution in clinical samples and antifungal susceptibility to five antifungals. From January 2013 through June 2015, 800 isolates were obtained from intensive care unit patients. Candida albicans (58.9%), Candida glabrata (20.4%), Candida krusei (8.6%), and Candida parapsilosis (3.6%) were the leading species. Majority of the C. albicans isolates were susceptible to the fluconazole. Elevated voriconazole minimal inhibitory concentrations (MICs) were observed in isolates exhibiting high fluconazole MICs, most frequently in C. glabrata. Isolates with echinocandins MICs suggesting reduced susceptibility were only sporadic cases with the exception of Trichosporon spp. The amphotericin B MICs were slightly higher for some C. krusei.

Combination of fluconazole with silver nanoparticles produced by Fusarium oxysporum improves antifungal effect against planktonic cells and biofilm of drug-resistant Candida albicans.

Silver nanoparticles (AgNPs) have been extensively studied because of their anti-microbial potential. Here, we evaluated the effect of biologically synthesized silver nanoparticles (AgNPbio) alone and in combination with fluconazole (FLC) against planktonic cells and biofilms of FLC-resistant Candida albicans AgNPbio exhibited a fungicidal effect, with a minimal inhibitory concentration (MIC) and fungicidal concentration ranging from 2.17 to 4.35 μg/ml. The combination of AgNPbio and FLC reduced the MIC of FLC around 16 to 64 times against planktonic cells of allC. albicans There was no significant inhibitory effect of AgNPbio on biofilm cells. However, FLC combined with AgNPbio caused a significant dose-dependent decrease in the viability of both initial and mature biofilm. All concentrations of AgNPbio, alone or in combination with FLC, were not cytotoxic to mammalian cells.The results highlight the effectiveness of the combination of AgNPbio with FLC against FLC-resistant C. albicans.

Comparison of Difference Between Fluconazole and Silver Nanoparticles in Antimicrobial Effect on Fluconazole-Resistant Candida Albicans Strains

Background: Opportunistic fungi cause fungal infections. Whereas some microorganisms are resistant to chemical drugs, scientists are looking for new natural and inorganic antimicrobial agents. The recent research on metal nanoparticles showed that silver nanoparticles (nanosilver) exhibits lower toxicity to mammalian cells and higher toxicity to microorganisms. Objectives: This study aimed to compare the difference between antimicrobial effect of nanosilver and some antibiotic agents on Candidaalbicans. Materials and Methods: We studied effect of fluconazole, nanosilver, and their combination on 20 fluconazole-resistant C. albicans from two centers and one standard sample (ATCC10261) by minimal inhibitory concentration (MIC) method. Results: Result of fungi static and fungicidal activities of nanosilver plus fluconazole on fluconazole-resistant C. albicans showed better inhibitory effect on the growth of standard C. albicans when MIC of fluconazole (8 µg/mL) combined with MIC of Nanosilver (0.0625 µg/mL). Conclusions: Totally, our results showed nanosilver caused an increase of at least nine-fold in inhibitory effect of fluconazole.

Antifungal susceptibility and drug-resistant mechanism of Trichosporon

Most cases of deep-seated trichosporonosis develop in patients with neutropenia, but it has recently been reported that breakthrough infections with Trichosporon species can develop during the use of candin family of antifungal agents. This is due to the primary resistance of the causal fungus, Trichosporon asahii (T. asahii), to the candin agents. On the other hand, there has been a case report of infection with Trichosporon that presented high-level resistance to the azole family of antifungal agents. Therefore, the possibility that the frequent use of azole agents may lead to secondary resistance to these agents is a cause for concern. Since trichosporonosis is a relatively rare infectious disease, there has been no established breakpoint for this fungus to various antifungal agents, wherein we cannot precisely confirm its sensitivity or resistance to the agents. However, our experiment demonstrated one of the processes for acquired drug resistance, wherein the minimal inhibitory concentration of fluconazole for T. asahii was markedly elevated after its long-term in vitro exposure to the drug. Although the mechanisms for drug-resistance of Trichosporon species are unknown, it is supposed that they are the same as the mechanisms found in Candida and Aspergillus species, namely, modification of target molecules or decrease of access to the molecules. Since cases of trichosporonosis are likely to increase in the future, we believe that there is an urgent need to establish the breakpoint for T. asahii based on large-scale drug sensitivity tests, as well as to elucidate its drug-resistance mechanisms.

The influence of tea tree oil (Melaleuca alternifolia) on fluconazole activity against fluconazole-resistant Candida albicans strains.

The aim of this study was to evaluate the activity of fluconazole against 32 clinical strains of fluconazole-resistant Candida albicans, and C. albicans ATCC 10231 reference strain, after their exposure to sublethal concentrations of tea tree oil (TTO) or its main bioactive component terpinen-4-ol. For all tested fluconazole-resistant C. albicans strains TTO and terpinen-4-ol minimal inhibitory concentrations (MICs) were low, ranging from 0.06% to 0.5%. The 24-hour exposure of fluconazole-resistant C. albicans strains to fluconazole with sublethal dose of TTO enhanced fluconazole activity against these strains. Overall, 62.5% of isolates were classified as susceptible, 25.0% exhibited intermediate susceptibility, and 12.5% were resistant. For all of the tested clinical strains the fluconazole MIC decreased from an average of 244.0 μg/mL to an average of 38.46 μg/mL, and the fluconazole minimal fungicidal concentrations (MFC) decreased from an average of 254.67 μg/mL to an average of 66.62 μg/mL. Terpinen-4-ol was found to be more active than TTO, and strongly enhanced fluconazole activity against fluconazole-resistant C. albicans strains. The results of this study demonstrate that combining natural substances such as TTO and conventional drug such as fluconazole, may help treat difficult yeast infections.

Molecular identification, genotyping, and antifungal susceptibility testing of clinically relevant Trichosporon species from Argentina

Trichosporon species are emerging causative agents of mycoses; most are documented in immunocompromised patients. Species identification is important for epidemiological purposes in order to better define species clinical associations and to improve antifungal treatment. Here, we studied a collection of 41 Trichosporon strains recovered from hospitalized patients in Argentina. All strains were identified by sequencing the D1/D2 domain of 26S, internal transcribed spacer (ITS) regions, and intergenic spacer 1 (IGS1) region. In addition, we determined the IGS1 region genotypes of the suspected T. asahii strains. Antifungal susceptibility of all strains was investigated. Thirty-eight of the 41 strains in this study were identified as follows: 29 T. asahii, 3 T. inkin, 3 T. montevideense, 2 T. faecale, and 1 T. dermatis. The identity of the three remaining strains could not be confirmed. Strain DMic 114126 (Culture collection of the Mycology Department (DMic), National Institute of Infectious Diseases "Dr. Carlos G. Malbrán".) may represent a T. asahii subspecies or a new Trichosporon species, strain DMic 94750 was identified as T. cf. guehoae and strain DMic 114132 as T. cf. akiyoshidainum. The distribution of T. asahii genotypes was as follows: 12 genotype 3, 9 genotype 1, 4 genotype 4, 2 genotype 5, and 2 genotype 7. Amphotericin B minimal inhibitory concentrations (MICs) were ≤1 mg/l for 78% (32/41) of the strains. Fluconazole MICs were ≥2 mg/l for 90% of the strains. However, itraconazole, voriconazole, ketoconazole, and posaconazole MICs were ≤1 mg/l for 100% of the strains. Terbinafine MICs were ≤1 mg/l for 98% 40/41 of the strains.