Dermatophytes growth curve and in vitro susceptibility test: a broth micro-titration method

Prevalence and characteristics of Epidermophyton floccosum skin infections: A 12-year retrospective study

BACKGROUND

Epidermophyton floccosum (E. floccosum), an anthropophilic dermatophyte, is the primary causative agent of skin conditions such as tinea cruris, tinea pedis and tinea corporis.

OBJECTIVES

This study aimed to determine the prevalence and characteristics of E. floccosum-induced dermatophytosis, with particular emphasis on the types of infections and demographic profiles.

METHODS

In this retrospective study, patient records from the dermatology outpatient clinic were scrutinized, covering the timeframe from January 2009 to December 2020. Eligibility for the study required a dermatophytosis diagnosis verified by microscopic examination and fungal culture.

RESULTS

Of the 4669 confirmed dermatophytosis cases, 82 (1.8%) were attributable to E. floccosum infection. The proportions of male and female patients with E. floccosum infections were 50.0% each. The most common presentation was tinea pedis (39.0%), followed by tinea cruris (37.8%) and tinea corporis (26.8%). The mean age at disease onset for tinea cruris was 38.7 ± 18.7 years, which was lower than that for tinea pedis (50.6 ± 14.2 years) and tinea corporis (53.5 ± 16.4 years). However, these age differences were not statistically significant. A continuous decrease in E. floccosum isolation was observed over the study period.

CONCLUSIONS

There was a steady decline in the prevalence of E. floccosum dermatophytosis over the 12-year study period. Despite the decreasing trend, tinea cruris, tinea corporis and tinea pedis remained the predominant clinical manifestations of E. floccosum infection.

Subtilisin 3 production from Microsporum canis is independent of keratin substrate availability

Dermatophytes are highly infectious fungi that cause superficial infections in keratinized tissues in humans and animals. This group of fungi is defined by their ability to digest keratin and encompasses a wide range of species. We investigated a critical adhesion protein, subtilisin 3, utilized by Microsporum canis during initial stages of infection, analyzing its production and expression under varying growth conditions. Additionally, as this protein must be expressed and produced for dermatophyte infections to occur, we developed and optimized a diagnostic antibody assay targeting this protein. Subtilisin 3 levels were increased in culture when grown in baffled flasks and supplemented with either l-cysteine or cat hair. As subtilisin 3 was also produced in cultures not supplemented with keratin or cysteine, this study demonstrated that subtilisin 3 production is not reliant on the presence of keratin or its derivatives. These findings could help direct future metabolic studies of dermatophytes, particularly during the adherence phase of infections.

Synergistic activity of the combination of falcarindiol and itraconazole in vitro against dermatophytes

Previous studies have shown that natural polyacetylene alcohols, such as falcarindiol (FADOH), have good antifungal effects on plant fungi. While its effect on fungi that infect humans remains to be explored. In our study, checkerboard microdilution, drop-plate assay, and time-growth method were employed to analyze the interactions between FADOH and itraconazole (ITC) in vitro against dermatophytes, including 12 Trichophyton rubrum (T. rubrum), 12 Trichophyton mentagrophytes (T. mentagrophytes), and 6 Microsporum canis (M. canis). The results showed that the combination of FADOH and ITC exhibited synergistic and additive activity against 86.7% of all tested dermatophytes. FADOH had an excellent synergistic effect on ITC against T. rubrum and T. mentagrophytes; the synergistic rates were 66.7% and 58.3%, respectively. On the contrary, FADOH combined with ITC showed poor synergistic inhibitory activity (16.7%) against M. canis. Moreover, the additive rates of these two drugs against T. rubrum, T. mentagrophytes, and M. canis were 25%, 41.7%, and 33.3%, respectively. No antagonistic interactions were observed. The drop-plate assay and time-growth curves confirmed that the combination of FADOH and ITC had a potent synergistic antifungal effect. The in vitro synergistic effect of FADOH and ITC against dermatophytes is reported here for the first time. Our findings suggest the potential use of FADOH as an effective antifungal drug in the combined therapy of dermatophytoses caused especially by T. rubrum and T. mentagrophytes.

Agastache honey has superior antifungal activity in comparison with important commercial honeys

There is an urgent need for new effective antifungal agents suitable for the treatment of superficial skin infections, since acquired resistance of fungi to currently available agents is increasing. The antifungal activity of mono-floral Agastache honey and commercially available honeys were tested against dermatophytes (T. mentagrophytes and T. rubrum) and C. albicans (ATCC 10231 and a clinical isolate) by agar well diffusion and micro-dilution (AWD and MD). In AWD and MD assays, Agastache honey was effective at 40% concentration against dermatophytes (zone diameter, 19.5–20 mm) and C. albicans with the same MIC and MFC values indicating fungicidal activity. Tea tree honey was effective at 80% concentration (zone diameter, 14 mm) against dermatophytes and at 40% concentration against T. mentagrophytes and C. albicans. Manuka was effective at 80% concentration only against T. mentagrophytes (zone diameter, 12 mm) and at 40% against T. rubrum and C. albicans with fungistatic activity. Similar to the AWD results, Jelly bush, Super Manuka, and Jarrah showed no activity against dermatophytes but showed some activity against C. albicans. Headspace volatiles of six honeys were isolated by SPME and identified by GC-MS. The characteristic chemical markers for each honey were as follows: Agastache- Phenol, 2,4-bis(1,1-dimethylethyl) and Estragole; Manuka and Tea-tree- Acetanisole and Methyl 3,5-dimethoxybenzoate; Jelly bush- Linalool and Nonanal; Super Manuka- Methyl 3,5-dimethoxybenzoate and Nonanal; Jarrah- Isophorone and Nonanoic acid. Overall, analysis of the bioactive compound content and antifungal activity of Agastache honey indicated possible use as an antifungal agent for management of superficial fungal infections.

Inhibitory Effects of Berberine Hydrochloride on Trichophyton mentagrophytes and the Underlying Mechanisms

BACKGROUND

T. mentagrophytes can infect all mammals, including rabbits, causing serious infections with remarkable economic losses for rabbit farmers. Berberine is an alkaloid that is effective against a variety of microbial infections such as T. mentagrophytes. Growth curve by dry weight determination and in-vivo antifungal assay were carried out to clarify the inhibitory effect of berberine hydrochloride against T. mentagrophytes. Transcriptomics analyses were also carried out for better understanding of the underlying mechanisms.

RESULTS

The growth rate of T. mentagrophytes was significantly higher in control condition than under berberine hydrochloride or clotrimazole for 60 h. The growth rate of T. mentagrophytes was significantly slighter higher in berberine condition (1 mg) than under clotrimazole for 46 h. T. mentagrophytes seriously shrunk after berberine or clotrimazole treatment, as observed by TEM and in SEM. Significant recovery was evident in three berberine groups on day 6 compared with the DMSO group. Results from transcriptomics analyses showed 18,881 identified unigenes, including 18,754 and 12,127 in the NT and SwissProt databases. Among these, 12,011, 9174, and 11,679 unigenes belonged to 3 Gene Ontology (GO), 43 KEGG, and 25 KOG categories, respectively. Interestingly, we found that down-regulation of 14α-demethylase exposed to various medicines was slightly different, i.e., berberine hydrochloride (fold change -3.4956) and clotrimazole (fold change -2.1283) caused various degrees of alteration.

CONCLUSIONS

Berberine hydrochloride could inhibit the growth of T. mentagrophytes. Berberine hydrochloride could also cure dermatosis induced by T. mentagrophytes. Down-regulation of 14α-demethylase exposed to various medicines was slightly different and might be one of the anti-resistance mechanisms of berberine hydrochloride in T. mentagrophytes. The present investigation provides considerable transcript sequence data that would help further assess the antifungal mechanisms against T. mentagrophytes, for antifungal medicine development.

Development and Application of a High-Throughput Screening Method to Evaluate Antifungal Activity against Trichophyton tonsurans

There exist relatively few drug classes on the market to treat dermatophyte infections. This investigation was designed to develop and validate high-throughput methodology for screening and confirmation of chemicals for activity against Trichophyton tonsurans. Growth characteristics were examined on two platforms (96- and 384-well) in three media at eight spore concentrations over a period of up to 120 h. Microspectrophotometry was used to automate plate reads. The 384-well platform was used to screen more than 7000 compounds from six chemical libraries. Z-scores for optical density relative to positive growth controls were used to flag compounds of interest and activity confirmed in separate assays. The final conditions selected for both screening and confirmation with minimum inhibitory concentration (MIC) determination were growth for 48 h at 32 °C in SabDex with 1 × 10(4) spores per reaction. Sensitivity and specificity averaged 99.2% (range, 95.2%-100%) and 99.8% (range, 99.1%-100%), respectively. MICs for known antifungals were similar to those reported by others using Clinical and Laboratory Standards Institute methods. Several novel compound classes were identified to have activity against T. tonsurans with potency comparable to known antifungals. A robust, reproducible assay is described that permits high-throughput screening in T. tonsurans.

Antifungal activity of berberine hydrochloride and palmatine hydrochloride against Microsporum canis -induced dermatitis in rabbits and underlying mechanism

Background

Phellodendron amurense, exhibits antifungal activity mainly by bioactive components including berberine hydrochloride and palmatine hydrochloride. This study was conducted to evaluate the antifungal effects of berberine hydrochloride, palmatine hydrochloride, and a mixture of both substances against Microsporum canis in vivo and in vitro.

Methods

The minimal inhibitory concentrations (MICs) of monomers and clotrimazole were determined using 1.5 % tryptic soy agar. The effects of these drugs on Microsporum canis growth was detected by determining dry weight. Transmission electron microscopy (TEM) was performed to observe the effect of chemicals on cell ultrastructure. Differential mRNA expressions of eight genes of M. canis treated with berberine or palmatine or their combination at different time points were determined by real-time PCR. NADH enzyme concentration was also detected. Clinical evaluation via in-vivo antifungal assay was also performed. Skin histology PAS staining was also carried out.

Results

Results showed that MICs of berberine, palmatine and clotrimazole were 1, 1, and 0.015 mg/mL, respectively. No significant difference was observed among the growth curves of the three groups before 18 h was reached. TEM showed that these drugs could destroy the cell membrane and organelles of M. canis at different time points. After 30 h of incubation, relative mRNA expressions of the genes in the combined group were significantly higher than those in the other groups including the clotrimazole group (P < 0.05); Palmatine initially induced the mRNA up-regulation of PGAL4, FSH1, PQ-LRP, NADH1 and NDR in M. canis; by contrast, berberine maintained a high expression level of these genes to shorten fungal life cycle and eradicate M. canis. Clinical results showed that combined treatment was more effective than single administration of each monomer or clotrimazole. Hence, berberine mixed with palmatine significantly elicited antifungal activities and could be used to treat M. canis in rabbits.

Conclusion

These results provide a comprehensive view of the mechanism of berberine and palmatine in anti-M. canis activity.

[Influence of the ecological group on the in vitro antifungal susceptibility of dermatophytic fungi]

BACKGROUND

Dermatophytes can be divided into geophilic (soil), zoophilic (animals) and anthropophilic (humans) strains, depending on the source of the keratin that they use for nutritional purposes.

AIMS

The in vitro susceptibility of clinical isolates of dermatophyte fungi has been studied in the 3 ecological groups with several antifungal agents for the topical management of dermatophytoses in order to determine their relationship with the ecological group.

METHODS

A standardised dilution micromethod in a liquid medium was used for the determination of the in vitro antifungal activity of 9 topical antifungal drugs: amorolfine (AMR), bifonazole (BFZ), clotrimazole, econazole, ketoconazole, miconazole, oxiconazole, terbinafine (TRB) and tioconazole. The in vitro activity was obtained against 124 clinical isolates of dermatophyte moulds from the anthropophilic, zoophilic and geophilic ecological groups.

RESULTS

The in vitro antifungal activity was different depending on the ecological group, although a species-dependent profile was also observed.

CONCLUSIONS

Azole derivatives showed a similar antifungal profile, being more active against anthropophilic dermatophytes > zoophilic > geophilic. Activity of TRB and AMR was different from that of azole derivatives (zoophilic > anthropophilic > geophilic). A higher in vitro antifungal activity against the 3 ecological groups was observed with TRB and AMR, whilst BFZ was the less active drug.

Sertaconazole antifungal profile determined by a microdilution method versus nine topical substances against dermatophyte fungi

Antifungal activity and in vitro inhibition time for sertaconazole (STZ) and 9 other topical drugs, namely amorolfine, bifonazole, clotrimazole, econazole, ketoconazole, miconazole, oxiconazole, terbinafine, and tioconazole were determined against 124 clinical isolates of dermatophyte (12 species) fungi by the microdilution method in a liquid medium and the measurement of optical density. STZ's antifungal activity was not always affected by the tested dermatophyte genus, as was the case with the remaining antifungals. In vitro antifungal activity was at the same level for all the studied azole derivatives, but, in terms of partial inhibitory concentrations, STZ starts its in vitro inhibitory activity in a shorter time than the other tested substances, particularly in those incubation periods when the growth of the dermatophyte fungi was more developed.

Antifungal activity of bis-azasqualenes, inhibitors of oxidosqualene cyclase

The antifungal activity and in vitro toxicity toward animal cells of two inhibitors of oxidosqualene cyclase, squalene bis-diethylamine (SBD) and squalene bis-diethylmethylammonium iodide (SBDI) were studied. Minimum inhibitory concentration (MIC) against dermatophytes and other fungi involved in cutaneous and systemic infections (12 isolates from seven species) were determined by the broth microdilution method based on the reference documents M38-A and M27-A2 of Clinical and Laboratory Standards Institute (CLSI). Both compounds exerted fungistatic activities, although with different action. SBDI was the more active compound and displayed low MIC values (in the 3.12-12.5 μg ml(-1) range) against Microsporum canis, Trichophyton mentagrophytes and one isolate of Scopulariopsis brevicaulis, while SBD showed MIC values against these species in the 3.12-25 μg ml(-1) range. Toxicity was tested on Madin-Darby canine kidney (MDCK) epithelial cells and human microvascular endothelial cells (HMEC). SBDI proved the less toxic compound: it inhibited M. canis, T. mentagrophytes and S. brevicaulis at concentrations below those found toxic for MDCK cells. HMEC were the more sensitive cells.

Sequenced dermatophyte strains: growth rate, conidiation, drug susceptibilities, and virulence in an invertebrate model

Although dermatophytes are the most common cause of fungal infections in the world, their basic biology is not well understood. The recent sequencing and annotation of the genomes of five representative dermatophyte species allows for the creation of hypotheses as to how they cause disease and have adapted to their distinct environments. An understanding of the microbiology of these strains will be essential for testing these hypotheses. This study is the first to generally characterize these five sequenced strains of dermatophytes for their microbiological aspects. We measured the growth rate on solid medium and found differences between species, with Microsporum gypseum CBS118893 having the fastest growth and Trichophyton rubrum CBS118892 the slowest. We also compared different media for conidia production and found that the highest numbers of conidia were produced when dermatophytes were grown on MAT agar. We determined the Minimum Inhibitory Concentration (MIC) of nine antifungal agents and confirmed susceptibility to antifungals commonly used as selectable markers. Finally, we tested virulence in the Galleria mellonella (wax moth) larvae model but found the results variable. These results increase our understanding of the microbiology and molecular biology of these dermatophyte strains and will be of use in advancing hypothesis-driven research about dermatophytes.

In vitro activity of Tachyplesin III alone and in combination with terbinafine against clinical isolates of dermatophytes

Aim of our study was to investigate the in vitro effects of Tachyplesin III (TP), a potent disulfide-linked peptide, in dermatophytes infections, with respect to or in combination with terbinafine (TERB), against 20 clinical isolates of dermatophytes belonging to four species. A broth microdilution method following the CLSI recommendations (M38-A) was used for testing drugs alone and in combination. TERB MICs were significantly lower than those observed for TP (p<0.001). Testing for antifungal agents in combination was performed for TERB with TP for all the 20 isolates. TERB activity in combination with TP showed indifferent activity for 14 of the 20 isolates (70%); synergic activity for 6 of the 20 isolates (30%); no antagonistic activity was observed. Further experiments were conducted with Microsporum canis 133, Trichophyton rubrum 62 and Trichophyton mentagrophytes 91 for fungal biomass. TP and TERB did not show a significant growth reduction compared to the control against T. mentagrophytes and T. rubrum. A significant difference of growth reduction both for TP and TERB compared to controls was observed for M. canis (p<0.01). In conclusion our study demonstrated that Tachyplesin III has potential activity against dermatophytes. In addition, we observed that the in vitro activity of Tachyplesin III can be enhanced upon combination with terbinafine. Synergy could permit lower doses of the individual antifungal agents to be used more effectively and/or safely.

Comparison of in vitro activity of five antifungal agents against dermatophytes, using the agar dilution and broth microdilution methods

The purpose of this study was to compare the agar dilution and broth microdilution methods for determining the minimum inhibitory concentration (MIC) of fluconazole, itraconazole, ketoconazole, griseofulvin and terbinafine for 60 dermatophyte samples belonging to the species Trichophyton rubrum, Trichophyton mentagrophytes and Microsporum canis. The percentage agreement between the two methods, for all the isolates with < 2 dilutions that were tested was 91.6% for ketoconazole and griseofulvin, 88.3% for itraconazole, 81.6% for terbinafine and 73.3% for fluconazole. One hundred percent agreement was obtained for Trichophyton mentagrophytes isolates evaluated with ketoconazole and griseofulvin. Thus, until a reference method for testing the in vitro susceptibility of dermatophytes is standardized, the similarity of the results between the two methods means that the agar dilution method may be useful for susceptibility testing on these filamentous fungi.

Antifungal resistance mechanisms in dermatophytes

Although fungi do not cause outbreaks or pandemics, the incidence of severe systemic fungal infections has increased significantly, mainly because of the explosive growth in the number of patients with compromised immune system. Thus, drug resistance in pathogenic fungi, including dermatophytes, is gaining importance. The molecular aspects involved in the resistance of dermatophytes to marketed antifungals and other cytotoxic drugs, such as modifications of target enzymes, over-expression of genes encoding ATP-binding cassette (ABC) transporters and stress-response-related proteins are reviewed. Emphasis is placed on the mechanisms used by dermatophytes to overcome the inhibitory action of terbinafine and survival in the host environment. The relevance of identifying new molecular targets, of expanding the understanding about the molecular mechanisms of resistance and of using this information to design new drugs or to modify those that have become ineffective is also discussed.